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muscle

 [mus´'l]
a bundle of long slender cells (muscle fibers) that have the power to contract and hence to produce movement. Muscles are responsible for locomotion and play an important part in performing vital body functions. They also protect the contents of the abdomen against injury and help support the body. See appendix 3-4 and see color plates.

Muscle fibers range in length from a few hundred thousandths of a centimeter to several centimeters. They also vary in shape, and in color from white to deep red. Each fiber receives its own nerve impulses, so that fine and varied motions are possible. Each has its small stored supply of glycogen, which it uses as fuel for energy. Muscles, especially the heart, also use free fatty acids as fuel. At the signal of an impulse traveling down the nerve, the muscle fiber changes chemical energy into mechanical energy, and the result is muscle contraction.

Some muscles are attached to bones by tendons. Others are attached to other muscles, or to skin (producing the smile, the wink, and other facial expressions, for example). All or part of the walls of hollow internal organs, such as the heart, stomach, intestines, and blood vessels, are composed of muscles. The last stages of swallowing and of peristalsis are actually series of contractions by the muscles in the walls of the organs involved.
Types of Muscle. There are three types of muscle: involuntary, voluntary, and cardiac, composed respectively of smooth, striated, and mixed smooth and striated tissue.
Types and structure of muscle. From Dorland's, 2000.


Involuntary muscles are those not under the control of the conscious part of the brain; they respond to the nerve impulses of the autonomic nervous system. They include the countless short-fibered, or smooth, muscles of the internal organs and power the digestive tract, the pupils of the eyes, and all other involuntary mechanisms.

Voluntary muscles are those controlled by the conscious part of the brain, and are striated. These are the skeletal muscles that enable the body to move, and there are more than 600 of them in the human body. Their fibers are grouped together in sheaths of muscle cells. Groups of fibers are bundled together into fascicles, surrounded by a tough sheet of connective tissue to form a muscle group such as the biceps. Unlike the involuntary muscles, which can remain in a state of contraction for long periods without tiring and are capable of sustained rhythmic contractions, the voluntary muscles are readily subject to fatigue.

Cardiac muscles (the muscles of the heart) are the third kind; they are involuntary and consist of striated fibers different from those of voluntary muscle. The contraction and relaxation of cardiac muscle continues at a rhythmic pace until death unless the muscle is injured in some way.
Voluntary muscles extend from one bone to another, cause movements by contraction, and work on the principle of leverage. For every direct action made by a muscle, an antagonistic muscle can cause an opposite movement. To flex the arm, the biceps contracts and the triceps relaxes; to extend the arm, the triceps contracts and the biceps relaxes.
(See also heart.)
Physiology of Muscles. No muscle stays completely relaxed, and as long as a person is conscious, it remains slightly contracted. This condition is called tonus, or tone. It keeps the bones in place and enables a posture to be maintained. It allows a person to remain standing, sitting up straight, kneeling, or in any other natural position. Muscles also have elasticity. They are capable of being stretched and of performing reflex actions. This is made possible by the motor and sensory nerves which serve the muscles.

Muscles enable the body to perform different types of movement. Those that bend a limb at a joint, raising a thigh or bending an elbow, are called flexors. Those that straighten a limb are called extensors. Others, the abductors, make possible movement away from the midline of the body, whereas the adductors permit movement toward the midline. Muscles always act in opposing groups. In bending an elbow or flexing a muscle, for example, the biceps (flexor) contracts and the triceps (extensor) relaxes. The reverse happens in straightening the elbow.

A muscle that has contracted many times, and has exhausted its stores of glycogen and other substances, and accumulated too much lactic acid, becomes unable to contract further and suffers from fatigue. In prolonged exhausting work, fat in the muscles can also be used for energy, and as a consequence the muscles become leaner.
agonistic muscle one opposed in action by another muscle, the antagonistic muscle. Called also agonist.
antagonistic muscle one that counteracts the action of another (the agonistic muscle). Called also antagonist.
appendicular muscle one of the muscles of a limb.
articular muscle one that has one end attached to the capsule of a joint.
auricular m's
1. the extrinsic auricular muscles, including the anterior, posterior, and superior auricular muscles. See appendix 3-4.
2. the intrinsic auricular muscles that extend from one part of the auricle to another, including the helicis major, helicis minor, tragicus, antitragicus, transverse auricular, and oblique auricular muscles. See appendix 3-4.
cruciate muscle a muscle in which the fiber bundles are arranged in the shape of an X.
cutaneous muscle striated muscle that inserts into the skin.
deltoid muscle the muscular cap of the shoulder, often used as a site for an intramuscular injection. See appendix 3-4.
extraocular m's the six voluntary muscles that move the eyeball: superior, inferior, middle, and lateral recti, and superior and inferior oblique muscles. See appendix 3-4.
extrinsic muscle one that originates in another part than that of its insertion, as those originating outside the eye, which move the eyeball.
fixation m's (fixator m's) accessory muscles that serve to steady a part.
gluteal m's three muscles, the greatest, middle, and least, that extend, abduct, and rotate the thigh. See appendix 3-4.
hamstring m's the muscles of the back of the thigh, including the biceps femoris, semitendinosus, and semimembranosus. See appendix 3-4.
intraocular m's the intrinsic muscles of the eyeball. See appendix 3-4.
intrinsic muscle one whose origin and insertion are both in the same part or organ, as those entirely within the eye.
multipennate muscle a muscle in which the fiber bundles converge to several tendons.
palatine m's the intrinsic and extrinsic muscles that act upon the soft palate.
pectoral m's four muscles of the chest; See appendix 3-4.
quadrate muscle a square-shaped muscle; see appendix 3-4.
quadriceps muscle a name applied collectively to four muscles of the thigh; see anatomic Table of Muscles in the Appendices.
scalene m's four muscles of the upper thorax that raise the first two ribs, aiding in respiration. See appendix 3-4.
skeletal m's striated muscles that are attached to bones and typically cross at least one joint.
sphincter muscle a ringlike muscle that closes a natural orifice; called also sphincter.
synergic m's (synergistic m's) those that assist one another in action.
thenar m's the abductor and flexor muscles of the thumb. See appendix 3-4.
triangular muscle a muscle that is triangular in shape.
yoked m's those that normally act simultaneously and equally, as in moving the eyes.

mus·cle

(mŭs'ĕl), [TA]
A primary tissue, consisting predominantly of highly specialized contractile cells, which may be classified as skeletal muscle, cardiac muscle, or smooth muscle; microscopically, the latter is lacking in transverse striations characteristic of the other two types; one of the contractile organs of the body by which movements of the various organs and parts are effected; typical muscle is a mass of musculus fibers (venter or belly), attached at each extremity, by means of a tendon, to a bone or other structure; the more proximal or more fixed attachment is called the origin (q.v.), the more distal or more movable attachment is the insertion (q.v.); the narrowing part of the belly that is attached to the tendon of origin is called the caput or head. For gross anatomic description, see musculus
Synonym(s): musculus [TA]
[L. musculus]

muscle

/mus·cle/ (mus´'l) an organ which by contraction produces movement of an animal organism.
abductor muscle of great toe  origin, medial tubercle of calcaneus, plantar fascia; insertion, medial surface of base of proximal phalanx of great toe; innervation, medial plantar; action, abducts, flexes great toe.
abductor muscle of little finger  origin, pisiform bone, tendon of ulnar flexor muscle of wrist; insertion, medial surface of base of proximal phalanx of little finger; innervation, ulnar; action, abducts little finger.
abductor muscle of little toe  origin, medial and lateral tubercles of calcaneus, plantar fascia; insertion, lateral surface of base of proximal phalanx of little toe; innervation, superficial branch of lateral plantar; action, abducts little toe.
abductor muscle of thumb, long  origin, posterior surfaces of radius and ulna; insertion, radial side of base of first metacarpal bone; innervation, posterior interosseous; action, abducts, extends thumb.
abductor muscle of thumb, short  origin, scaphoid, ridge of trapezium, transverse carpal ligament; insertion, lateral surface of base of proximal phalanx of thumb; innervation, median; action, abducts thumb.
adductor muscle, great  origin, deep part—inferior ramus of pubis, ramus of ischium, superficial part—ischial tuberosity; insertion, deep part—linea aspera of femur, superficial part—adductor tubercle of femur; innervation, deep part—obturator, superficial part—sciatic; action, deep part—adducts thigh, superficial part—extends thigh.
adductor muscle, long  origin, crest and symphysis of pubis; insertion, linea aspera of femur; innervation, obturator; action, adducts, rotates, flexes thigh.
adductor muscle, short  origin, outer surface of inferior ramus of pubis; insertion, upper part of linea aspera of femur; innervation, obturator; action, adducts, rotates, flexes thigh.
adductor muscle, smallest  a name given the anterior portion of the great adductor muscle; insertion, ischium, body and ramus of pubis; innervation, obturator and sciatic; action, adducts thigh.
adductor muscle of great toe  : origin, oblique head—bases of second, third, and fourth metatarsals, and sheath of peroneus longus, transverse head— capsules of metatarsophalangeal joints of three lateral toes; insertion, lateral side of base of proximal phalanx of great toe; innervation, lateral plantar; action, adducts great toe.
agonistic muscle  one opposed in action by another muscle (the antagonistic m.).
anconeus muscle  origin, back of lateral epicondyle of humerus; insertion, olecranon and posterior surface of ulna; innervation, radial; action, extends forearm.
antagonistic muscle  one that counteracts the action of another muscle (the agonistic m.).
antitragicus muscle  origin, outer part of antitragus; insertion, caudate process of helix and anthelix; innervation, temporal and posterior auricular.
arrector muscle of hair  origin, papillary layer of skin; insertion, a hair follicle; innervation, sympathetic; action, elevate a hair of skin.
articular muscle  one that has one end attached to a joint capsule.
articular muscle of elbow  a few fibers of the deep surface of the triceps brachii that insert into the posterior ligament and synovial membrane of the elbow joint.
articular muscle of knee  origin, distal fourth of anterior surface of shaft of femur; insertion, synovial membrane of knee joint; innervation, femoral; action, lifts capsule of knee joint.
aryepiglottic muscle  an inconstant fascicle of the oblique arytenoid muscle, originating from the apex of the arytenoid cartilage and inserting on the lateral margin of the epiglottis.
arytenoid muscle, oblique  one of the intrinsic muscles of the larynx; origin, dorsal aspect of muscular process of arytenoid cartilage; insertion, apex of opposite arytenoid cartilage; innervation, recurrent laryngeal; action, closes inlet of larynx.
arytenoid muscle, transverse  one of the intrinsic muscles of the larynx; origin, dorsal aspect of muscular process of arytenoid cartilage; insertion, continuous with thyroarytenoid, apex of opposite cartilage; innervation, recurrent laryngeal; action, approximates arytenoid cartilages.
auricular muscles 
1. the extrinsic auricular muscles, including the anterior, posterior, and superior auricular muscles.
2. the intrinsic auricular muscles that extend from one part of the auricle to another, including the helicis major, helicis minor, tragicus, antitragicus, transverse auricular, and oblique auricular muscles.
auricular muscle, anterior  origin, superficial temporal fascia; insertion, cartilage of ear; innervation, facial; action, draws the auricle forward.
auricular muscle, posterior  origin, mastoid process; insertion, cartilage of ear; innervation, facial; action, draws auricle backward.
auricular muscle, superior  origin, galea aponeurotica; insertion, cartilage of ear; innervation, facial; action, raises auricle.
Bell's muscle  the muscular strands between the ureteric orifices and the uvula vesicae, bounding the trigone of the urinary bladder.
biceps muscle of arm  origin, long head—upper border of glenoid cavity, short head—apex of coracoid process; insertion, radial tuberosity and fascia of forearm; innervation, musculocutaneous; action, flexes forearm, supinates hand.
biceps muscle of thigh  origin, long head—ischial tuberosity, short head—linea aspera of femur; insertion, head of fibula, lateral condyle of tibia; innervation, long head—tibial, short head— peroneal, popliteal; action, flexes leg, extends thigh.
brachial muscle  origin, anterior surface of humerus; insertion, coronoid process of ulna; innervation, radial, musculocutaneous; action, flexes forearm.
brachioradial muscle  origin, lateral supracondylar ridge of humerus; insertion, lower end of radius; innervation, radial; action, flexes forearm.
bronchoesophageal muscle  a name given muscular fasciculi arising from the wall of the left bronchus, reinforcing muscles of the esophagus.
Brücke's muscle  the longitudinal fibers of the ciliary muscle.
buccinator muscle  origin, buccinator ridge of mandible, alveolar process of maxilla, pterygomandibular ligament; insertion, orbicularm muscle of mouth at angle of mouth; innervation, buccal branch of facial; action, compresses cheek and retracts angle of the mouth.
bulbocavernosus muscle , bulbocavernous muscle, bulbospongiosus muscle origin, central point of perineum, median raphe of bulb; insertion, fascia of penis (male) or clitoris (female); innervation, pudendal; action, constricts spongy urethra.
canine muscle  levator m. of angle of mouth.
cardiac muscle  the muscle of the heart, composed of striated but involuntary muscle fibers, comprising the chief component of the myocardium and lining the walls of the adjoining large vessels.
ceratocricoid muscle  a muscular fasciculus arising from the cricoid cartilage and inserted on the inferior cornu of the thyroid cartilage, considered one of the intrinsic muscles of the larynx.
cervical muscles  the muscles of the neck, including the sternocleidomastoid, longus colli, suprahyoid, infrahyoid, and scalene muscles.
chin muscle  origin, incisive fossa of mandible; insertion, skin of chin; innervation, facial; action, wrinkles skin of chin.
chondroglossus muscle  origin, medial side and base of lesser cornu of hyoid bone; insertion, substance of tongue; innervation, hypoglossal; action, depresses, retracts tongue.
ciliary muscle  origin, scleral spur; insertion, outer layers of choroid and ciliary processes; innervation, oculomotor, parasympathetic; action, affects shape of lens in visual accommodation.
coccygeal muscle , coccygeus muscle origin, ischial spine; insertion, lateral border of lower part of sacrum, upper coccyx; innervation, third and fourth sacral; action, supports and raises coccyx.
constrictor muscle of pharynx, inferior  origin, undersurfaces of cricoid and thyroid cartilages; insertion, median raphe of posterior wall of pharynx; innervation, glossopharyngeal, pharyngeal plexus, and external and recurrent laryngeal; action, constricts pharynx. It is divided into a cricopharyngeal part and a thyropharyngeal part.
constrictor muscle of pharynx, middle  origin, cornua of hyoid and stylohyoid ligament; insertion, median raphe of posterior wall of pharynx; innervation, pharyngeal plexus of vagus and glossopharyngeal; action, constricts pharynx. It is divided into a ceratopharyngeal part and an chondropharyngeal part.
constrictor muscle of pharynx, superior  origin, medial pterygoid plate, pterygomandibular raphe, mylohyoid ridge of mandible, and mucous membrane of floor of mouth; insertion, median raphe of posterior wall of pharynx; innervation, pharyngeal plexus of vagus; action, constricts pharynx. It is divided into buccopharyngeal, glossopharyngeal, mylopharyngeal, and pterygopharyngeal parts.
coracobrachial muscle  origin, coracoid process of scapula; insertion, medial surface of shaft of humerus; innervation, musculocutaneous; action, flexes, adducts arm.
corrugator muscle, superciliary  origin, medial end of superciliary arch; insertion, skin of eyebrow; innervation, facial; action, draws eyebrow downward and medially.
cremaster muscle  origin, inferior margin of internal oblique muscle of abdomen; insertion, pubic tubercle; innervation, genital branch of genitofemoral; action, elevates testis.
cricoarytenoid muscle, lateral  one of the intrinsic muscles of the larynx; origin, lateral surface of cricoid cartilage; insertion, muscular process of arytenoid cartilage; innervation, recurrent laryngeal; action, approximates vocal folds.
cricoarytenoid muscle, posterior  one of the intrinsic muscles of the larynx; origin, back of cricoid cartilage; insertion, muscular process of arytenoid cartilage; innervation, recurrent laryngeal; action, separates vocal folds.
cricothyroid muscle  one of the intrinsic muscles of the larynx; origin, front and side of cricoid cartilage; insertion, lamina of thyroid cartilage; innervation, superior laryngeal; action, tenses vocal folds.
dartos muscle 
1. the nonstriated muscle fibers of the tunica dartos, the deeper layers of which help to form the septum of the scrotum.
2. tunica dartos (1).
deltoid muscle  origin, clavicle, acromion, spine of scapula; insertion, deltoid tuberosity of humerus; innervation, axillary; action, abducts, flexes, extends arm.
depressor muscle, superciliary  a name applied to a few fibers of the orbital part of the orbicular muscle of eye that are inserted in the eyebrow, which they depress.
depressor muscle of angle of mouth  origin, lower border of mandible; insertion, angle of mouth; innervation, facial; action, pulls down angle of mouth.
depressor muscle of lower lip  origin, anterior portion of lower border of mandible; insertion, orbicular muscle of mouth and skin of lower lip; innervation, facial; action, depresses lower lip.
depressor muscle of septum of nose  origin, incisor fossa of maxilla; insertion, ala and septum of nose; innervation, facial; action, contracts nostril and depresses ala.
detrusor muscle of bladder , detrusor urinae muscle the bundles of smooth muscle fibers forming the muscular coat of the urinary bladder, which are arranged in a longitudinal and a circular layer and, on contraction, serve to expel urine.
diaphragmatic muscle  diaphragma (1).
digastric muscle  origin, anterior belly—digastric fossa on deep surface of inferior border of mandible near symphysis, posterior belly—mastoid notch of temporal bone; insertion, intermediate tendon on hyoid bone; innervation, anterior belly—mylohyoid, posterior belly—digastric branch of facial; action, elevates hyoid bone, lowers jaw.
dilator muscle of pupil  a name applied to fibers extending radially from the sphincter of pupil to the ciliary margin; innervation, sympathetic; action, dilates iris.
epicranial muscle  a name given the muscular covering of the scalp, including the occipitofrontal and temporoparietal muscles, and the galea aponeurotica.
erector muscle of spine  a name given the fibers of the more superficial of the deep muscles of the back, originating from the sacrum, spines of the lumbar and the eleventh and twelfth thoracic vertebrae, and the iliac crest, which split and insert as the iliocostal, longissimus, and spinal muscles.
muscles of expression  a group of cutaneous muscles of the facial structures, including the muscles of the scalp, ear, eyelids, nose, and mouth, and the platysma.
extensor muscle of fingers  origin, lateral epicondyle of humerus; insertion, common extensor tendon of each finger; innervation, posterior interosseus; action, extends wrist joint and phalanges.
extensor muscle of great toe, long  origin, front of fibula and interosseous membrane; insertion, dorsal surface of base of distal phalanx of great toe; innervation, deep peroneal; action, dorsiflexes ankle joint, extends great toe.
extensor muscle of great toe, short  a name given the portion of the short extensor muscle of toes that goes to the great toe.
extensor muscle of index finger  origin, dorsal surface of body of ulna, interosseous membrane; insertion, common extensor tendon of index finger; innervation, posterior interosseous; action, extends index finger.
extensor muscle of little finger  origin, common extensor tendon; insertion, tendon of extensor muscle of fingers to little finger; innervation, deep radial; action, extends little finger.
extensor muscle of thumb, long  origin, dorsal surface of ulna and interosseous membrane; insertion, dorsal surface of distal phalanx of thumb; innervation, posterior interosseous; action, extends, abducts thumb.
extensor muscle of thumb, short  origin, dorsal surface of radius and interosseous membrane; insertion, dorsal surface of proximal phalanx of thumb; innervation, posterior interosseous; action, extends thumb.
extensor muscle of toes, long  origin, anterior surface of fibula, lateral condyle of tibia, interosseous membrane; insertion, common extensor tendon of four lateral toes: innervation, deep peroneal; action, extends toes.
extensor muscle of toes, short  origin, dorsal surface of calcaneus; insertion, extensor tendons of first, second, third, fourth toes; innervation, deep peroneal; action, extends toes.
extensor muscle of wrist, radial, long  origin, lateral supracondylar ridge of humerus; insertion, base of second metacarpal bone; innervation, radial; action, extends and abducts wrist joint.
extensor muscle of wrist, radial, short  short radial extensor muscle of wrist: origin, lateral epicondyle of humerus, insertion, base of third metacarpal bone; innervation, radial; action, extends and abducts wrist joint.
extensor muscle of wrist, ulnar  origin, humeral head—lateral epicondyle of humerus, ulnar head—dorsal border of ulna; insertion, base of fifth metacarpal bone; innervation, deep radial; action, extends and adducts wrist joint.
extraocular muscles  the six voluntary muscles that move the eyeball: superior, inferior, middle, and lateral recti, and superior and inferior oblique muscles.
extrinsic muscle  one not originating in the limb or part in which it is inserted.
facial muscles  m's of expression.
fibular muscle, long  origin, lateral condyle of tibia, head and lateral surface of fibula; insertion, medial cuneiform, first metatarsal; innervation, superficial peroneal; action, abducts, everts, plantar flexes foot.
fibular muscle, short  origin, lateral surface of fibula; insertion, base of fifth metatarsal bone; innervation, superficial peroneal; action, abducts, plantar flexes foot.
fibular muscle, third  origin, anterior surface of fibula, interosseous membrane; insertion, fifth metatarsal; innervation, deep peroneal; action, everts, dorsiflexes foot.
fixation muscles , fixator muscles accessory muscles that serve to steady a part.
flexor muscle of fingers, deep  origin, shaft of ulna, coronoid process; insertion, distal phalanges of fingers; innervation, ulnar and anterior interosseous; action, flexes distal phalanges.
flexor muscle of fingers, superficial  origin, humeroulnar head—medial epicondyle of humerus, coronoid process of ulna, radial head— oblique line of radius, anterior border; insertion, middle phalanges of fingers; innervation, median; action, flexes middle phalanges.
flexor muscle of great toe, long  origin, posterior surface of fibula; insertion, base of distal phalanx of great toe; innervation, tibial; action, flexes great toe.
flexor muscle of great toe, short  origin, undersurface of cuboid, lateral cuneiform; insertion, base of proximal phalanx of great toe; innervation, medial plantar; action, flexes great toe.
flexor muscle of little finger, short  origin, hook of hamate bone, transverse carpal ligament; insertion, medial side of proximal phalanx of little finger; innervation, ulnar; action, flexes little finger.
flexor muscle of little toe, short  origin, base of fifth metatarsal, sheath of long peroneal muscle; insertion, lateral surface of base of proximal phalanx of little toe; innervation, lateral plantar; action, flexes little toe.
flexor muscle of thumb, long  origin, anterior surface of radius and coronoid process of ulna; insertion, base of distal phalanx of thumb; innervation, anterior interosseous; action, flexes thumb.
flexor muscle of thumb, short  origin, flexor retinaculum, ridge of trapezium; insertion, base of proximal phalanx of thumb; innervation, median, ulnar; action, flexes and adducts thumb.
flexor muscle of toes, long  origin, posterior surface of shaft of tibia; insertion, distal phalanges of four lateral toes; innervation, posterior tibial; action, flexes toes and extends foot.
flexor muscle of toes, short  origin, medial tuberosity of calcaneus, plantar fascia; insertion, middle phalanges of four lateral toes; innervation, medial plantar; action, flexes toes.
flexor muscle of wrist, radial  origin, medial epicondyle of humerus; insertion, base of second metacarpal; innervation, median; action, flexes and abducts wrist joint.
flexor muscle of wrist, ulnar  origin, humeral head—medial epicondyle of humerus, ulnar head—olecranon, ulna, intermuscular septum; insertion, pisiform, hook of hamate, proximal end of fifth metacarpal; innervation, ulnar; action, flexes and adducts wrist joint.
gastrocnemius muscle  origin, medial head—popliteal surface of femur, upper part of medial condyle, and capsule of knee, lateral head—lateral condyle and capsule of knee; insertion, aponeurosis unites with tendon of soleus to form calcaneal tendon (Achilles tendon); innervation, tibial; action, plantar flexes ankle joint, flexes knee joint.
gemellus muscle, inferior  origin, tuberosity of ischium; insertion, greater trochanter of femur; innervation, nerve to quadrate muscle of thigh; action, rotates thigh laterally.
gemellus muscle, superior  origin, spine of ischium; insertion, greater trochanter of femur; innervation, nerve to internal obturator; action, rotates thigh laterally.
genioglossus muscle  origin, mental spine of mandible; insertion, hyoid bone and inferior surface of tongue; innervation, hypoglossal; action, protrudes and depresses tongue.
geniohyoid muscle  origin, mental spine of mandible; insertion, body of hyoid bone; innervation, a branch of first cervical nerve through hypoglossal; action, elevates, draws hyoid forward.
glossopalatine muscle  palatoglossus m.
gluteal muscle, greatest  gluteus maximus m.
gluteal muscle, middle  gluteus medius m.
gluteal muscle, least  gluteus minimus m.
gluteus maximus muscle  origin, lateral surface of ilium, dorsal surface of sacrum and coccyx, sacrotuberous ligament; insertion, iliotibial tract of fascia lata, gluteal tuberosity of femur; innervation, inferior gluteal; action, extends, abducts, and rotates thigh laterally.
gluteus medius muscle  origin, lateral surface of ilium between anterior and posterior gluteal lines; insertion, greater trochanter of femur; innervation, superior gluteal; action, abducts and rotates thigh medially.
gluteus minimus muscle  origin, lateral surface of ilium between anterior and inferior gluteal lines; insertion, greater trochanter of femur; innervation, superior gluteal; action, abducts, rotates thigh medially.
gracilis muscle  origin, lower half of body and entire inferior ramus of pubis; insertion, medial surface of shaft of tibia; innervation, obturator; action, adducts thigh, flexes knee joint.
hamstring muscles  the muscles of the back of the thigh: biceps femoris, semitendinous, and semimembranous muscles.
muscle of helix, greater  origin, spine of helix; insertion, anterior border of helix; innervation, auriculotemporal and posterior auricular (branches of facial); action, tenses skin of auditory canal.
muscle of helix, lesser  origin, anterior rim of helix; insertion, concha; innervation, temporal, posterior auricular.
Horner's muscle  the lacrimal part of the orbicular muscle of eye.
Houston's muscle  fibers of the bulbocavernosus muscle compressing the dorsal vein of the penis.
intrinsic muscle  one whose origin and insertion are in the same part or organ.
hyoglossus muscle  origin, body and greater cornu of hyoid bone; insertion, side of tongue; innervation, hypoglossal; action, depresses and retracts tongue.
iliac muscle  origin, iliac fossa and base of sacrum; insertion, greater psoas tendon and lesser trochanter of femur; innervation, femoral; action, flexes thigh, trunk on limb.
iliococcygeus muscle  the posterior portion of the levator ani which originates as far anteriorly as the obturator canal and inserts on the side of the coccyx and the anococcygeal body; innervation, third and fourth sacral; action, helps to support pelvic viscera and resist increases in intra-abdominal pressure.
iliocostal muscle  the lateral division of the erector muscle of spine.
iliocostal muscle of loins  origin, iliac crest; insertion, angles of lower six or seven ribs; innervation, branches of thoracic and lumbar; action, extends lumbar spine.
iliocostal muscle of neck  origin, angles of third, fourth, fifth, and sixth ribs; insertion, transverse processes of fourth, fifth, and sixth cervical vertebrae; innervation, branches of cervical; action, extends cervical spine.
iliocostal muscle of thorax  origin, upper borders of angles of six lower ribs; insertion, angles of six upper ribs and transverse process of seventh cervical vertebra; innervation, branches of thoracic; action, keeps thoracic spine erect.
iliopsoas muscle  a compound muscle consisting of the iliac and psoas major muscles.
incisive muscles of inferior lip  small bundles of muscle fibers, one arising from the incisive fossa of the mandible on each side and passing laterally to the angle of the mouth.
incisive muscles of superior lip  small bundles of muscle fibers, one arising from the incisive fossa of the maxilla on each side and passing laterally to the angle of the mouth.
infraspinous muscle  origin, infraspinous fossa of scapula; insertion, greater tubercle of humerus; innervation, suprascapular; action, rotates humerus laterally.
intercostal muscles, external 
1. musculi intercostales externi.
2. origin, inferior border of rib; insertion, superior border of rib below; innervation, intercostal; action, draw ribs together in respiration and expulsive movements.
intercostal muscles, innermost  the layer of muscle fibers separated from the internal intercostal muscles by the intercostal nerves.
intercostal muscles, internal  origin, inferior border of rib and costal cartilage; insertion, superior border of rib and costal cartilage below; innervation, intercostal; action, draw ribs together in respiration and expulsive movements.
interosseous muscles, palmar  origin, sides of second, fourth, and fifth metacarpal bones; insertion, extensor tendons of second, fourth, and fifth fingers; innervation, ulnar; action, adduct, flex proximal phalanges, extend middle and distal phalanges.
interosseous muscles, plantar  origin, medial surface of third, fourth, and fifth metatarsal bones; insertion, medial side of base of proximal phalanges of third, fourth, and fifth toes; innervation, lateral plantar; action, adduct, flex toes.
interosseous muscles of foot, dorsal  origin, adjacent surfaces of metatarsal bones; insertion, base of proximal phalanges of second, third, and fourth toes; innervation, lateral plantar; action, abduct, flex toes.
interosseous muscles of hand, dorsal  origin, by two heads from adjacent sides of metacarpal bones; insertion, extensor tendons of second, third, and fourth fingers; innervation, ulnar; action, abduct, flex proximal phalanges.
interspinal muscles  short bands of muscle fibers between spinous processes of contiguous vertebrae; innervation, spinal; action, extend vertebral column.
interspinal muscles of loins  paired bands of muscle fibers extending between spinous processes of contiguous lumbar vertebrae, innervated by spinal nerves, and acting to extend the vertebral column.
interspinal muscles of neck  paired bands of muscle fibers extending between spinous processes of contiguous cervical vertebrae, innervated by spinal nerves, and acting to extend the vertebral column.
interspinal muscles of thorax  paired bands of muscle fibers extending between spinous processes of contiguous thoracic vertebrae, innervated by spinal nerves, and acting to extend the vertebral column.
intertransverse muscles  small muscles passing between the transverse processes of contiguous vertebrae, including the lateral and medial intertransverse muscles of the loins, the intertransverse muscles of the thorax, and the anterior and posterior intertransverse muscles of the neck.
involuntary muscle  one that is not under the control of the will.
ischiocavernous muscle  origin, ramus of ischium; insertion, crus of penis (crus of clitoris); innervation, perineal; action, maintains erection of penis (clitoris).
Landström's muscle  minute muscle fibers in the fascia around and behind the eyeball, attached in front to the anterior orbital fascia and eyelids.
latissimus dorsi muscle  origin, spines of lower thoracic vertebrae, lumbar and sacral vertebrae through thoracolumbar fascia, iliac crest, lower ribs, inferior angle of scapula; insertion, floor of intertubercular sulcus of humerus; innervation, thoracodorsal; action, adducts, extends, and rotates humerus medially.
levator muscle of angle of mouth  origin, canine fossa of maxilla; insertion, orbicularis oris and skin at angle of mouth; innervation, facial; action, raises angle of mouth.
levator ani muscle  a name applied collectively to important muscular components of the pelvic diaphragm, arising mainly from the back of the body of pubis and running backward toward the coccyx, including the pubococcygeus (levator muscle of prostate in male and pubovaginal in female), puborectal, and iliococcygeus muscles.
levator muscle of prostate  a part of the anterior portion of the pubococcygeus muscle, inserted in the prostate and the tendinous center of the perineum; innervated by sacral and pudendal nerves, it supports and compresses the prostate and is involved in control of micturition.
levator muscles of ribs  originating from the transverse processes of the seventh cervical and first to eleventh thoracic vertebrae and inserting medial to the angle of a lower rib; innervated by intercostal nerves and aiding in elevation of the ribs in respiration.
levator muscle of scapula  origin, transverse processes of four upper cervical vertebrae; insertion, medial border of scapula; innervation, third and fourth cervical; action, raises scapula.
levator muscle of thyroid gland  an inconstant muscle originating on the isthmus or pyramid of the thyroid gland and inserting on the body of the hyoid bone.
levator muscle of upper eyelid  origin, upper border of optic foramen; insertion, tarsal plate and skin of upper eyelid; innervation, oculomotor; action, raises upper lid.
levator muscle of upper lip  origin, lower orbital margin; insertion, muscle of upper lip; innervation, facial nerve; action, raises upper lip.
levator muscle of upper lip and ala of nose  origin, nasal process of maxilla; insertion, cartilage and skin of ala nasi, and upper lip; innervation, infraorbital branch of facial; action, raises upper lip and dilates nostril.
levator muscle of velum palatinum  origin, apex of petrous portion of temporal bone and cartilaginous part of auditory tube; insertion, aponeurosis of soft palate; innervation, pharyngeal plexus of vagus; action, raises soft palate.
lingual muscles  the extrinsic and intrinsic muscles that move the tongue.
long muscle of head  origin, transverse processes of third to sixth cervical vertebrae; insertion, basal portion of occipital bone; innervation, branches from first, second, and third cervical; action, flexes head.
long muscle of neck  origin, superior oblique portion—transverse processes of third to fifth cervical vertebrae; inferior oblique portion—bodies of first to third thoracic vertebrae; vertical portion—bodies of three upper thoracic and three lower cervical vertebrae; insertion, superior oblique portion—tubercle of anterior arch of atlas; inferior oblique portion—transverse processes of fifth and sixth cervical vertebrae; vertical portion— bodies of second to fourth cervical vertebrae; innervation, anterior cervical. action, flexes and supports cervical vertebrae.
longissimus muscle of head  origin, transverse processes of four or five upper thoracic vertebrae, articular processes of three or four lower cervical vertebrae; insertion, mastoid process of temporal bone; innervation, branches of cervical; action, draws head backward, rotates head.
longissimus muscle of neck  origin, transverse processes of four or five upper thoracic vertebrae; insertion, transverse processes of second to sixth cervical vertebrae; innervation, lower cervical and upper thoracic; action, extends cervical vertebrae.
longissimus muscle of thorax  origin, transverse and articular processes of lumbar vertebrae and thoracolumbar fascia; insertion, transverse processes of all thoracic vertebrae, nine or ten lower ribs; innervation, lumbar and thoracic; action, extends thoracic vertebrae.
longitudinal muscle of tongue, inferior  origin, inferior surface of tongue at base; insertion, tip of tongue; innervation, hypoglossal; action, changes shape of tongue in mastication and deglutition.
longitudinal muscle of tongue, superior  origin, submucosa and septum of tongue; insertion, margins of tongue; innervation, hypoglossal; action, changes shape of tongue in mastication and deglutition.
lumbrical muscles of foot  origin, tendons of long flexor muscles of toes; insertion, extensor tendons of four lateral toes; innervation, medial and lateral plantar; action, flex metatarsophalangeal joints, extend distal phalanges.
lumbrical muscles of hand  origin, tendons of deep flexor muscles of fingers; insertion, extensor tendons of four lateral fingers; innervation, median and ulnar; action, flex metacarpophalangeal joint and extend middle and distal phalanges.
masseter muscle  origin, superficial part—zygomatic process of maxilla and inferior border of zygomatic arch, deep part—inferior border and medial surface of zygomatic arch; insertion, superficial part—angle and ramus of mandible, deep part—superior half of ramus and lateral surface of coronoid process of mandible; innervation, mandibular division of trigeminal; action, raises mandible, closes jaws.
masticatory muscles  a group of muscles responsible for the movement of the jaws during mastication, including the masseter. temporal, and medial and lateral pterygoid muscles.
Müller's muscle 
1. the circular fibers of the ciliary muscle.
2. orbital muscle.
multifidus muscles  origin, sacrum, sacroiliac ligament, mammillary processes of lumbar, transverse processes of thoracic, and articular processes of cervical vertebrae; insertion, spines of contiguous vertebrae above; innervation, dorsal branches of spinal nerves; action, extend, rotate vertebral column.
mylohyoid muscle  origin, mylohyoid line of mandible; insertion, body of hyoid bone and median raphe; innervation, mylohyoid branch of inferior alveolar; action, elevates hyoid bone, supports floor of mouth.
nasal muscle  origin, maxilla; insertion, alar part—ala of nose, transverse part—by aponeurotic expansion with fellow of opposite side; innervation, facial; action, alar part—aids in widening nostril, transverse part—depresses cartilage of nose.
oblique muscle of abdomen, external  origin, lower eight ribs at costal cartilages; insertion, crest of ilium, linea alba through rectus sheath; innervation, lower intercostal; action, flexes and rotates vertebral column, compresses abdominal viscera.
oblique muscle of abdomen, internal  origin, inguinal ligament, iliac crest, thoracolumbar fascia; insertion, inferior three or four costal cartilages, linea alba, conjoined tendon to pubis; innervation, lower intercostal; action, flexes and rotates vertebral column, compresses abdominal viscera.
oblique muscle of auricle  origin, cranial surface of concha; insertion, cranial surface of auricle above concha; innervation, temporal and posterior auricular (branches of facial).
oblique muscle of eyeball, inferior  origin, orbital plate of maxilla; insertion, sclera; innervation, oculomotor; action, rotates eyeball upward and outward.
oblique muscle of eyeball, superior  origin, lesser wing of sphenoid above optic foramen; insertion, sclera; innervation, trochlear; action, rotates eyeball downward and outward.
oblique muscle of head, inferior  origin, spinous process of axis; insertion, transverse process of atlas; innervation, dorsal branches of spinal nerves; action, rotates atlas and head.
oblique muscle of head, superior  origin, transverse process of atlas; insertion, occipital bone; innervation, dorsal branches of spinal nerves; action, extends and moves head laterally.
obturator muscle, external  origin, pubis, ischium, and superficial surface of obturator membrane; insertion, trochanteric fossa of femur; innervation, obturator; action, rotates thigh laterally.
obturator muscle, internal  origin, pelvic surface of hip bone, margin of obturator foramen, ramus of ischium, inferior ramus of pubis, internal surface of obturator membrane; insertion, greater trochanter of femur; innervation, fifth lumbar, first and second sacral; action, rotates thigh laterally.
occipitofrontal muscle  origin, frontal belly—galea aponeurotica, occipital belly— highest nuchal line of occipital bone; insertion, frontal belly—skin of eyebrows and root of nose, occipital belly—galea aponeurotica; innervation, frontal belly—temporal branch of facial, occipital belly—posterior auricular branch of facial; action, frontal belly—raises eyebrows, occipital belly—draws scalp posteriorly.
omohyoid muscle  a muscle comprising two bellies (superior and inferior) connected by a central tendon that is bound to the clavicle by a fibrous expansion of the cervical fascia; origin, superior border of scapula; insertion, lateral border of hyoid bone; innervation, upper cervical through ansa cervicalis; action, depresses hyoid bone.
opposing muscle of little finger  origin, hook of hamate bone, transverse carpal ligament; insertion W>, medial aspect of fifth metacarpal; innervation, eighth cervical through ulnar; action, rotates, abducts, and flexes fifth metacarpal.
opposing muscle of thumb  origin, ridge of trapezium, flexor retinaculum; insertion, radial side of first metacarpal; innervation, sixth and seventh cervical through median; action, flexes and opposes thumb.
orbicular muscle  one that encircles a body opening, e.g., the eye or mouth.
orbicular muscle of eye , orbicularis oculi muscle the oval sphincter muscle surrounding the eyelids, consisting of three parts: origin, orbital part—medial margin of orbit, including frontal process of maxilla, palpebral part—medial canthus, medial palpebral ligament, lacrimal part—posterior lacrimal crest; insertion, orbital part—near origin after encircling orbit, palpebral part—fibers intertwine to form lateral palpebral raphe, lacrimal part—lateral palpebral raphe, upper and lower tarsi; innervation, facial; action, closes eyelids, wrinkles forehead, compresses lacrimal sac.
orbicular muscle of mouth  a name applied to a complicated sphincter muscle of mouth, comprising a labial part, fibers restricted to the lips, and a marginal part, fibers blending with those of adjacent muscles; innervation, facial; action, closes and protrudes lips.
orbital muscle  a thin layer of nonstriated muscle that bridges the inferior orbital fissure and inserts in the fascia of inferior orbital fissure; innervation, sympathetic branches; action, protrudes eye.
palatoglossus muscle  origin, undersurface of soft palate; insertion, side of tongue; innervation, pharyngeal plexus of vagus; action, elevates tongue, constricts fauces.
palatopharyngeal muscle  one of the intrinsic muscles of the larynx; origin, soft palate; insertion, aponeurosis of pharynx, dorsal border of thyroid cartilage; innervation, pharyngeal plexus of vagus; action, aids in deglutition.
palmar muscle, long  origin, medial epicondyle of humerus; insertion, flexor retinaculum, palmar aponeurosis; innervation, median; action, flexes wrist joint.
palmar muscle, short  origin, palmar aponeurosis; insertion, skin of medial border of hand; innervation, ulnar; action, assists in deepening hollow of palm.
papillary muscles  conical muscular projections from the walls of the cardiac ventricles, attached to the cusps of the atrioventricular valves by the chordae tendineae. There is an anterior and a posterior papillary muscle in each ventricle, as well as a group of small papillary muscles on the septum in the right ventricle.
pectinate muscles  a name applied to small ridges of muscle fibers projecting from the inner walls of the auricles of the heart, and extending in the right atrium from the auricle to the crista terminalis.
pectineal muscle  origin, pectineal line of pubis; insertion, femur distal to lesser trochanter; innervation, obturator and femoral; action, flexes, adducts thigh.
pectoral muscle, greater  origin, clavicle, sternum, six upper ribs, aponeurosis of external oblique muscle of abdomen. These origins are reflected in the subdivision of the muscle into clavicular, sternocostal, and abdominal parts; insertion, crest of greater tubercle of humerus; innervation, medial and lateral pectoral; action, adducts, flexes, rotates arm medially.
pectoral muscle, smaller  origin, third, fourth, and fifth ribs; insertion, coracoid process of scapula; innervation, lateral and medial pectoral; action, draws shoulder forward and downward, raises third, fourth, and fifth ribs in forced inspiration.
peroneal muscle, long  long fibular m.
peroneal muscle, short  short fibular m.
peroneal muscle, third  third fibular m.
pharyngeal muscles  the muscular coat of the pharynx, comprising the three constrictor muscles and the stylopharyngeal, salpingopharyngeal, and palatopharyngeal muscles.
piriform muscle  origin, ilium, second to fourth sacral vertebrae; insertion, upper border of greater trochanter; innervation, first and second sacral; action, rotates thigh laterally.
plantar muscle  origin, oblique popliteal ligament, lateral supracondylar line of femur; insertion, posterior part of calcaneus; innervation, tibial; action, plantar flexes foot.
pleuroesophageal muscle  a bundle of smooth muscle usually connecting the esophagus with the left mediastinal pleura.
popliteal muscle  origin, lateral condyle of femur, lateral meniscus; insertion, posterior surface of tibia; innervation, tibial; action, flexes leg, rotates leg medially.
procerus muscle  origin, fascia over nasal bone; insertion, skin of forehead; innervation, facial; action, draws medial angle of eyebrows down.
pronator muscle, quadrate  pronator quadratus m.
pronator muscle, round  pronator teres m.
pronator quadratus muscle  origin, anterior surface and border of distal third or fourth of ulna; insertion, anterior surface and border of distal fourth of shaft of radius; innervation, anterior interosseous; action, pronates hand.
pronator teres muscle  origin, humeral head—medial epicondyle of humerus, ulnar head— coronoid process of ulna; insertion, lateral surface of radius; innervation, median; action, pronates hand and flexes elbow.
psoas muscle, greater  origin, lumbar vertebrae; insertion, lesser trochanter of femur; innervation, second and third lumbar; action, flexes thigh or trunk.
psoas muscle, smaller  origin, last thoracic and first lumbar vertebrae; insertion, arcuate line, iliopectineal eminence, iliac fascia; innervation, first lumbar; action, flexes trunk.
pterygoid muscle, external  lateral pterygoid m.
pterygoid muscle, internal  medial pterygoid m.
pterygoid muscle, lateral  origin, superior head—lateral surface of greater wing of sphenoid and infratemporal crest; inferior head—lateral surface of lateral pterygoid plate; insertion, neck of condyle of mandible, temporomandibular joint capsule; innervation, mandibular division of trigeminal; action, protrudes mandible, opens jaws, moves mandible from side to side.
pterygoid muscle, medial  origin, lateral pterygoid plate, tuberosity of maxilla; insertion, medial surface of ramus and angle of mandible; innervation, mandibular division of trigeminal; action, closes jaws.
pubococcygeus muscle  the anterior portion of the levator ani muscle, originating anterior to the obturator canal; insertion, anococcygeal ligament and side of coccyx; innervation, third and fourth sacral; action, helps support pelvic viscera and resist increases in intra-abdominal pressure.
puboprostatic muscle  smooth muscle fibers contained within the medial puboprostatic ligament, which pass from the prostate anteriorly to the pubic bone.
puborectal muscle  a portion of the levator ani muscle having a more lateral origin from the pubic bone, and continuous posteriorly with the corresponding muscle of the opposite side; innervation, third and fourth sacral; action, helps support pelvic viscera and resist increases in intra-abdominal pressure.
pubovaginal muscle  a part of the anterior portion of the pubococcygeus muscle, which is inserted into the urethra and vagina; innervated by the sacral and pudendal nerves, it is involved in control of micturition.
pubovesical muscle  smooth muscle fibers extending from the neck of the urinary bladder to the pubis.
pyloric sphincter muscle  pyloric sphincter.
pyramidal muscle  origin, anterior aspect of pubis, anterior pubic ligament; insertion, linea alba; innervation, last thoracic; action, tenses abdominal wall.
pyramidal muscle of auricle  an inconstant prolongation of the fibers of the muscle of tragus to the spine of helix.
quadrate muscle of loins  origin, crest of ilium, thoracolumbar fascia, lumbar vertebrae; insertion, twelfth rib, transverse processes of four upper lumbar vertebrae; innervation, first and second lumbar and twelfth thoracic; action, flexes lumbar vertebrae laterally.
quadrate muscle of lower lip  depressor m. of lower lip.
quadrate muscle of sole  origin, calcaneus and plantar fascia; insertion, tendons of long flexor muscle of toes; innervation, lateral plantar; action, aids in flexing toes.
quadrate muscle of thigh  origin, upper part of lateral border of tuberosity of ischium; insertion, quadrate tubercle of femur, intertrochanteric crest; innervation, fourth and fifth lumbar and first sacral; action, adducts, rotates thigh laterally.
quadrate muscle of upper lip  levator m. of upper lip.
quadriceps muscle of thigh  a name applied collectively to the rectus muscle of thigh and the intermediate, lateral, and medial vastus muscles, inserting by a common tendon that surrounds the patella and ends on the tuberosity of the tibia, and acting to extend the leg upon the thigh.
rectococcygeus muscle  smooth muscle fibers originating on the anterior surface of the second and third coccygeal vertebrae and inserting on the posterior surface of the rectum, innervated by autonomic nerves, and acting to retract and elevate the rectum.
rectourethral muscles  bands of smooth muscle fibers extending from the perineal flexure of the rectum to the membranous urethra in the male.
rectouterine muscle  a band of fibers running between the cervix of the uterus and the rectum, in the rectouterine fold.
rectovesical muscle  a band of fibers in the male, connecting the longitudinal musculature of the rectum with the external muscular coat of the bladder.
rectus abdominis muscle  origin, pubis; insertion, xiphoid process, cartilages of fifth, sixth, and seventh ribs; innervation, branches of lower thoracic; action, flexes lumbar vertebrae, supports abdomen.
rectus muscle of eyeball, inferior  origin, common tendinous ring; insertion, underside of sclera; innervation, oculomotor; action, adducts, rotates eyeball downward and medially.
rectus muscle of eyeball, lateral  origin, common tendinous ring; insertion, lateral side of sclera; innervation, abducens; action, abducts eyeball.
rectus muscle of eyeball, medial  origin, common tendinous ring; insertion, medial side of sclera; innervation, oculomotor; action, adducts eyeball.
rectus muscle of eyeball, superior  origin, common tendinous ring; insertion, upper aspect of sclera; innervation, oculomotor; action, adducts, rotates eyeball upward and medially.
rectus muscle of head, anterior  origin, lateral mass of atlas; insertion, basilar process of occipital bone; innervation, first and second cervical; action, flexes, supports head.
rectus muscle of head, lateral  origin, upper surface of transverse process of atlas; insertion, jugular process of occipital bone; innervation, first and second cervical; action, flexes, supports head.
rectus muscle of head, posterior, greater  origin, spinous process of axis; insertion, occipital bone; innervation, suboccipital and greater occipital; action, extends head.
rectus muscle of head, posterior, lesser  origin, tubercle on dorsal arch of atlas; insertion, occipital bone; innervation, suboccipital and greater occipital; action, extends head.
rectus muscle of thigh  origin, anterior inferior iliac spine, rim of acetabulum; insertion, patella, tubercle of tibia; innervation, femoral; action, extends leg, flexes thigh.
Reisseisen's muscles  the smooth muscle fibers of the smallest bronchi.
rhomboid muscle, greater  origin, spinous processes of second, third, fourth, and fifth thoracic vertebrae; insertion, medial margin of scapula; innervation, dorsal scapular; action, retracts, elevates scapula.
rhomboid muscle, lesser  origin, spinous processes of seventh cervical to first thoracic vertebrae, lower part of nuchal ligament; insertion, medial margin of scapula at root of the spine; innervation, dorsal scapular; action, adducts, elevates scapula.
risorius muscle  origin, fascia over masseter; insertion, skin at angle of mouth; innervation, buccal branch of facial; action, draws angle of mouth laterally.
rotator muscles  a series of small muscles deep in the groove between the spinous and transverse processes of the vertebrae; innervation, spinal; action, extend and rotate vertebral column toward opposite side.
Ruysch's muscle  the muscular tissue of the fundus uteri.
sacrococcygeal muscle, anterior  a musculotendinous slip passing from the lower sacral vertebrae to the coccyx.
sacrococcygeal muscle, posterior  a muscular slip passing from the posterior aspect of the sacrum to the coccyx.
sacrospinal muscle  erector m. of spine.
salpingopharyngeal muscle  origin, auditory tube near its orifice; insertion, posterior part of palatopharyngeal muscle; innervation, pharyngeal plexus of vagus; action, raises nasopharynx.
sartorius muscle  origin, anterior superior iliac spine; insertion, medial side of proximal end of tibia; innervation, femoral; action, flexes thigh and leg.
scalene muscle, anterior  origin, transverse processes of third to sixth cervical vertebrae; insertion, scalene tubercle of first rib; innervation, second to seventh cervical; action, raises first rib, flexes cervical vertebrae forward and laterally, rotates cervical vertebrae to opposite side.
scalene muscle, middle  origin, transverse processes of second to sixth cervical vertebrae; insertion, upper surface of first rib; innervation, second to seventh cervical; action, raises first rib, flexes cervical vertebrae laterally.
scalene muscle, posterior  origin, posterior tubercles of transverse processes of fourth to sixth cervical vertebrae; insertion, second rib; innervation, second to seventh cervical; action, raises first and second ribs, flexes cervical vertebrae laterally.
scalene muscle, smallest  a band occasionally found between the anterior and middle scalene muscles.
semimembranous muscle  origin, tuberosity of ischium; insertion, medial condyle and border of tibia, lateral condyle of femur; innervation, tibial; action, flexes and rotates leg medially, extends thigh.
semipennate muscle  a muscle in which the fiber bundles approach the tendon of insertion from only one direction and are inserted through only a small segment of its circumference.
semispinal muscle of head  origin, transverse processes of five or six upper thoracic and four lower cervical vertebrae; insertion, occipital bone; innervation, suboccipital, greater occipital, and branches of cervical; action, extends head.
semispinal muscle of neck  origin, transverse processes of five or six upper thoracic vertebrae; insertion, spinous processes of second to fifth cervical vertebrae; innervation, branches of cervical; action, extends, rotates vertebral column.
semispinal muscle of thorax  origin, transverse processes of sixth to tenth thoracic vertebrae; insertion, spinous processes of two lower cervical and four upper thoracic vertebrae; innervation, spinal nerves; action, extends, rotates vertebral column.
semitendinous muscle  origin, tuberosity of ischium; insertion, upper part of medial surface of tibia; innervation, tibial; action, flexes and rotates leg medially, extends thigh.
serratus muscle, anterior  origin, eight or nine upper ribs; insertion, medial border of scapula; innervation, long thoracic; action, draws scapula forward; rotates scapula to raise shoulder in abduction of arm.
serratus muscle, inferior posterior  origin, spines of two lower thoracic and two or three upper lumbar vertebrae; insertion, inferior border of four lower ribs; innervation, ninth to twelfth thoracic; action, lowers ribs in expiration.
serratus muscle, superior posterior  origin, nuchal ligament, spinous processes of upper thoracic vertebrae; insertion, second, third, fourth, and fifth ribs; innervation, first four thoracic; action, raises ribs in inspiration.
skeletal muscles  striated muscles attached to bones, which cross at least one joint.
smooth muscle  nonstriated, involuntary muscle.
soleus muscle  origin, fibula, popliteal fascia, tibia; insertion, calcaneus by Achilles tendon; innervation, tibial; action, plantar flexes foot.
sphincter muscle of anus, external  origin, tip of coccyx, anococcygeal ligament; insertion, tendinous center of perineum; innervation, inferior rectal and fourth sacral; action, closes anus.
sphincter muscle of anus, internal  a thickening of the circular lamina of the muscular tunic at the caudal end of the rectum.
sphincter muscle of bile duct  an annular sheath of muscle that invests the bile duct within the wall of the duodenum.
sphincter muscle of female urethra, external  origin, ramus of pubis; insertion, median raphe behind and in front of urethra; innervation, perineal; action, compresses the central part of the urethra.
sphincter muscle of hepatopancreatic ampulla  sphincter of Oddi.
sphincter muscle of male urethra, external  origin, ramus of pubis; insertion, median raphe behind and in front of urethra; innervation, perineal; action, compresses the membranous part of the urethra.
sphincter muscle of pupil  circular fibers of the iris, innervated by the ciliary nerves (parasympathetic), and acting to contract the pupil.
sphincter muscle of pylorus  pyloric sphincter.
sphincter muscle of urethra, internal , sphincter muscle of urinary bladder a circular layer of smooth muscle fibers surrounding the internal urethral orifice in males, innervated by the vesical nerve, and acting to close the internal orifice of the urethra. No such structure exists in females.
spinal muscle of head  origin, spines of upper thoracic and lower cervical vertebrae; insertion, occipital bone; innervation, spinal nerves; action, extends head.
spinal muscle of neck  origin, spinous processes of seventh cervical and sometimes two upper thoracic vertebrae; insertion, spinous processes of axis and sometimes of second to fourth cervical vertebrae; innervation, branches of cervical; action, extends vertebral column.
spinal muscle of thorax  origin, spinous processes of two upper lumbar and two lower thoracic; insertion, spines of upper thoracic vertebrae; innervation, branches of spinal nerves; action, extends vertebral column.
splenius muscle of head  origin, lower half of nuchal ligament, spines of seventh cervical and three upper thoracic vertebrae; insertion, mastoid process of temporal bone, occipital bone; innervation, middle and lower cervical; action, extends, rotates head.
splenius muscle of neck  origin, spinous processes of third to sixth thoracic vertebrae; insertion, transverse processes of two or three upper cervical vertebrae; innervation, dorsal branches of lower cervical; action, extends, rotates head and neck.
stapedius muscle  origin, interior of pyramid of tympanic cavity; insertion, posterior surface of neck of stapes; innervation, stapedial branch of facial; action, dampens stapedial movement.
sternal muscle  a band occasionally found parallel to the sternum on the sternocostal head of the greater pectoral muscle.
sternocleidomastoid muscle  origin, sternal head—manubrium, clavicular head—clavicle; insertion, mastoid process and superior nuchal line of occipital bone; innervation, accessory nerve and cervical plexus; action, flexes vertebral column, rotates head.
sternocostal muscle  transverse m. of thorax.
sternohyoid muscle  origin, manubrium and clavicle; insertion, body of hyoid bone; innervation, upper ansa cervicalis; action, depresses hyoid bone and larynx.
sternothyroid muscle  origin, manubrium; insertion, lamina of thyroid cartilage; innervation, ansa cervicalis; action, depresses thyroid cartilage.
striated muscle , striped muscle any muscle whose fibers are divided by transverse bands into striations; such muscles are voluntary.
styloglossus muscle  origin, styloid process; insertion, margin of tongue; innervation, hypoglossal; action, raises and retracts tongue.
stylohyoid muscle  origin, styloid process; insertion, body of hyoid bone; innervation, facial; action, draws hyoid and tongue superiorly and posteriorly.
stylopharyngeus muscle  one of the intrinsic muscles of the larynx; origin, styloid process; insertion, thyroid cartilage and pharyngeal constrictors; innervation, pharyngeal plexus, glossopharyngeal; action, raises and dilates pharynx.
subclavius muscle  origin, first rib and its cartilage; insertion, lower surface of clavicle; innervation, fifth and sixth cervical; action, depresses lateral end of clavicle.
subcostal muscles  origin, inner surface of ribs: insertion, inner surface of first, second, third rib below; innervation, intercostal; action, draw adjacent ribs together, depress ribs.
subscapular muscle  origin, subscapular fossa of scapula; insertion, lesser tubercle of humerus; innervation, subscapular; action, rotates humerus medially.
supinator muscle  origin, lateral epicondyle of humerus, ulna, elbow joint fascia; insertion, radius; innervation, deep radial; action, supinates hand.
supraspinous muscle  origin, supraspinous fossa of scapula; insertion, greater tubercle of humerus; innervation, suprascapular; action, abducts humerus.
suspensory muscle of duodenum  a flat band of smooth muscle originating from the left crus of the diaphragm, and continuous with the muscular coat of the duodenum at its junction with the jejunum.
synergic muscles , synergistic muscles those that assist one another in action.
tarsal muscle, inferior  origin, inferior rectus muscle; insertion, tarsal plate of lower eyelid; innervation, sympathetic; action, widens palpebral fissure.
tarsal muscle, superior  origin, levator muscle of upper eyelid; insertion, tarsal plate of upper eyelid; innervation, sympathetic; action, widens palpebral fissure.
temporal muscle  origin, temporal fossa and fascia; insertion, coronoid process of mandible; innervation, mandibular; action, closes jaws.
temporoparietal muscle  origin, temporal fascia above ear; insertion, galea aponeurotica; innervation, temporal branches of facial; action, tightens scalp.
tensor muscle of fascia lata  origin, iliac crest; insertion, iliotibial band of fascia lata; innervation, superior gluteal; action, flexes, rotates thigh medially.
tensor tympani muscle , tensor muscle of tympanic membrane origin, cartilaginous portion of auditory tube; insertion, manubrium of malleus; innervation, mandibular; action, tenses tympanic membrane.
tensor veli palatini muscle , tensor muscle of velum palatinum origin, scaphoid fossa of pterygoid process, wall of auditory tube, spine of sphenoid; insertion, aponeurosis of soft palate, horizontal part of palatine bone; innervation, mandibular; action, tenses soft palate, opens auditory tube.
teres major muscle  origin, inferior angle of scapula; insertion, crest of intertubercular sulcus of humerus; innervation, lower subscapular; action, adducts, extends, rotates arm medially.
teres minor muscle  origin, lateral margin of scapula; insertion, greater tuberosity of humerus; innervation, axillary; action, rotates arm laterally.
muscle of terminal notch  an inconstant muscular slip continuing forward from the muscle of tragus to bridge the cartilaginous part of the meatus.
thenar muscles  the abductor and flexor muscles of the thumb.
thyroarytenoid muscle  one of the intrinsic muscles of the larynx; origin, lamina of thyroid cartilage; insertion, muscular process of arytenoid cartilage; innervation, recurrent laryngeal; action, relaxes, shortens vocal folds.
thyroepiglottic muscle  fibers of the thyroarytenoid muscle that continue to the margin of the epiglottis; it closes the inlet to the larynx.
thyrohyoid muscle  origin, lamina of thyroid cartilage; insertion, greater cornu of hyoid bone; innervation, first cervical; action, raises and changes form of larynx.
tibial muscle, anterior  origin, lateral condyle and lateral surface of tibia, interosseous membrane; insertion, medial cuneiform and base of first metatarsal; innervation, deep peroneal; action, dorsiflexes and inverts foot.
tibial muscle, posterior  origin, tibia, fibula, interosseous membrane; insertion, bases of second to fourth metatarsals and tarsals, except talus; innervation, tibial; action, plantar flexes and inverts foot.
tracheal muscle  a transverse layer of smooth fibers in the dorsal portion of the trachea; insertion, tracheal cartilages; innervation, autonomic fibers; action, lessens caliber of trachea.
muscle of tragus  a short, flattened vertical band on the lateral surface of the tragus, innervated by the auriculotemporal and posterior auricular nerves.
transverse abdominal muscle  origin, cartilages of six lower ribs, thoracolumbar fascia, iliac crest, inguinal ligament; insertion, linea alba through rectus sheath, conjoined tendon to pubis; innervation, lower intercostals, iliohypogastric, ilioinguinal; action, compresses abdominal viscera.
transverse muscle of auricle  origin, cranial surface of auricle; insertion, circumference of auricle; innervation, posterior auricular; action, retracts helix.
transverse muscle of chin  superficial fibers of the depressor muscle of the angle of the mouth which turn medially and cross to the opposite side.
transverse muscle of neck  a small muscle often present, passing from the occipital protuberance to the posterior auricular muscle; it may be either superficial or deep to the trapezius muscle.
transverse perineal muscle, deep  origin, ramus of ischium; insertion, tendinous center of perineum; innervation, perineal; action, fixes tendinous center of perineum.
transverse perineal muscle, superficial  origin, ramus of ischium; insertion, tendinous center of perineum; innervation, perineal; action, fixes tendinous center of perineum.
transverse muscle of thorax  origin, mediastinal surface of sternum and of xiphoid process; insertion, cartilages of second to sixth ribs; innervation, intercostal; action, draws ribs downward.
transverse muscle of tongue  origin, median septum of tongue; insertion, dorsum and margins of tongue; innervation, hypoglossal; action, changes shape of tongue in mastication and deglutition.
transversospinal muscles  a name applied collectively to the semispinal, multifidus, and rotator muscles.
trapezius muscle  origin, occipital bone, nuchal ligament, spinous processes of seventh cervical and all thoracic vertebrae; insertion, clavicle, acromion, spine of scapula; innervation, accessory nerve and cervical plexus; action, rotates scapula to raise shoulder in abduction of arm, draws scapula backward.
triangular muscle  a muscle that is triangular in shape.
triceps muscle of arm , triceps brachii muscle origin, long head—infraglenoid tubercle of scapula, lateral head—posterior surface of humerus, lateral border of humerus, lateral intermuscular septum, medial head—posterior surface of humerus below radial groove, medial border of humerus, medial intermuscular septa; insertion, olecranon of ulna; innervation, radial; action, extends forearm, long head adducts and extends arm.
triceps muscle of calf , triceps surae muscle the gastrocnemius and soleus muscles considered together.
muscle of uvula  origin, posterior nasal spine of palatine bone and aponeurosis of soft palate; insertion, uvula; innervation, pharyngeal plexus of vagus; action, raises uvula.
vastus muscle, intermediate  origin, anterior and lateral surfaces of femur; insertion, patella, common tendon of quadriceps muscle of thigh; innervation, femoral; action, extends leg.
vastus muscle, lateral  origin, capsule of hip joint, lateral aspect of femur; insertion, patella, common tendon of quadriceps muscle of thigh; innervation, femoral; action, extends leg.
vastus muscle, medial  origin, medial aspect of femur; insertion, patella, common tendon of quadriceps muscle of thigh; innervation, femoral; action, extends leg.
vertical muscle of tongue  origin, dorsal fascia of tongue; insertion, sides and base of tongue; innervation, hypoglossal; action, changes shape of tongue in mastication and deglutition.
vocal muscle  one of the intrinsic muscles of the larynx; origin, angle between laminae of thyroid cartilage; insertion, vocal process of arytenoid cartilage; innervation, recurrent laryngeal; action, shortens and relaxes vocal folds.
voluntary muscle  any muscle that is normally under the control of the will.
yoked muscles  those that normally act simultaneously and equally, as in moving the eyes.
zygomatic muscle, greater  origin, zygomatic bone in front of temporal process; insertion, angle of mouth; innervation, facial; action, draws angle of mouth backward and upward.
zygomatic muscle, lesser  origin, zygomatic bone near maxillary suture; insertion, orbicular muscle of mouth and levator muscle of upper lip; innervation, facial; action, draws upper lip upward and laterally.

muscle

(mŭs′əl)
n.
1. A tissue composed of fibers capable of contracting to effect bodily movement.
2. A contractile organ consisting of a special bundle of muscle tissue, which moves a particular bone, part, or substance of the body: the heart muscle; the muscles of the arm.
3. Muscular strength: enough muscle to be a high jumper.

mus′cly adj.

muscle (m)

[mus′əl]
Etymology: L, musculus
a kind of tissue composed of fibers or cells that is able to contract, causing movement of body parts and organs. Muscle fibers are richly vascular, excitable, conductive, and elastic. There are two basic kinds-striated muscle and smooth muscle. Striated muscle, which composes all skeletal muscles except the myocardium, is long and voluntary. It responds very quickly to stimulation and is paralyzed by interruption of its innervation. Smooth muscle, of which all visceral muscles are composed, is short and involuntary. It reacts slowly to all stimuli and does not entirely lose its tone if innervation is interrupted. The myocardium is sometimes classified as a third (cardiac) kind of muscle, but it is basically a striated muscle that does not contract as quickly as the striated muscles of the rest of the body. See also cardiac muscle.

MUSCLE

Abbreviation for:
Multi Station Clinical Examination (OSCE)

mus·cle

(mŭs'ĕl) [TA]
A primary tissue, consisting predominantly of highly specialized contractile cells, which may be classified as skeletal muscle, cardiac muscle, or smooth muscle; microscopically, the latter is lacking in transverse striations characteristic of the other two types; one of the contractile organs of the body by which movements of the various organs and parts are effected; typical muscle is a mass of muscle fibers (venter or belly), attached at each extremity, by means of a tendon, to a bone or other structure; the more proximal or more fixed attachment is called the origin, the more distal or more movable attachment is the insertion; the narrowing part of the belly that is attached to the tendon of origin is called the caput or head.
Synonym(s): musculus.
[L. musculus]

muscle

(mus'el ) [L. musculus, diminutive of mus, mouse]
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MORPHOLOGICAL FORMS OF MUSCLE
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MORPHOLOGICAL FORMS OF MUSCLE
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MORPHOLOGICAL FORMS OF MUSCLE
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MORPHOLOGICAL FORMS OF MUSCLE
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MORPHOLOGICAL FORMS OF MUSCLE
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MORPHOLOGICAL FORMS OF MUSCLE
A type of tissue composed of contractile cells. Each muscle cell is filled with parallel actin and myosin filaments. When activated by an internal release of calcium, the filaments use the energy in ATP to crawl along each other in opposite directions. This movement shortens the length of the cell, which then contracts.

The three general classes of muscle cells (myocytes) are skeletal (striated), cardiac (striated), and smooth; most of the muscle in humans is skeletal. A typical muscle has a central portion called the belly and two or more attachment ends with tendons; the more stationary of the attachments is called the muscle's origin, while the more movable attachment is called the muscle's insertion. See: illustration

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MUSCLES OF THE TRUNK

abdominal muscles

The abdominal muscles are made up of the cremaster, external abdominal oblique, iliacus, psoas major, pyramidalis, quadratus lumborum, rectus abdominis, and transversus abdominis muscles.
illustration

abducens muscle

, abducens oculi
Lateral rectus muscle, one of the extraocular muscles. Nerve: cranial nerve (CN VI). In clinical practice, referred to as the lateral rectus muscle.

abductor muscle

A muscle that on contraction draws a part away from the median plane of the body or the axial line of an extremity.
See: adductor muscle

abductor digiti minimi muscle

Hand muscle. Origin: pisiform bone of wrist. Insertion: base of proximal phalanx of digit 5. Nerve: ulnar (C8-T1). Action: abducts digit 5.

abductor pollicis brevis muscle

Hand muscle. Origin: flexor retinaculum of wrist, scaphoid and trapezium bones. Insertion: lateral base of proximal phalanx of thumb. Nerve: median (C8-T1). Action: abducts thumb, aides in opposition with digit 5.
See: armfor illus. (Muscles of the Arm)

adductor muscle

A muscle that draws toward the midline.
See: abductor muscle

adductor brevis muscle

A muscle of the medial thigh originating on the ramus of the pubis and inserted in the linea aspera of the femur. It adducts, flexes, and medially rotates the thigh and is controlled by the obturator nerve.

adductor longus muscle

Hip and thigh muscle. Origin: front of pubis (below crest). Insertion: linea aspera of femur. Nerve: obturator (L2-L4). Action: adducts, flexes, and rotates thigh medially.
See: leg for illus. (Muscles of the leg)

adductor magnus muscle

Hip and thigh muscle. Origin: inferior ramus of pubis, ramus of ischium, ischial tuberosity. Insertion: linea aspera and adductor tubercle of femur. Nerve: obturator and sciatic (L2-L4). Action: adducts, flexes, and rotates thigh medially.
See: leg for illus. (Muscles of the leg)

adductor pollicis muscle

Hand muscle. Origin: capitate bone of wrist and metacarpals 2-3. Insertion: proximal phalanx of thumb and medial sesamoid bone. Nerve: ulnar (C8-T1. Action: adducts thumb, aides in opposition with digit 5.

agonist muscle

Controlled movements involve two opposing muscles: the agonist muscle produces the main action, while the antagonist muscle produces the opposite action to a lesser degree. The balance between agonist and antagonist muscles allows precise control of the final action.
Synonym: antagonist muscle See: PNF Stretching Techniques

anconeus muscle

A short muscle along the back of and outside the elbow. It originates from the lateral epicondyle of the humerus, crosses the back of the elbow joint on the same side, attaches to the lateral surface of the olecranon process and the adjacent surface of the ulna. It extends the forearm and abducts the elbow as the forearm pronates. It is innervated by the radial nerve (C7, C8, T1).

antagonist muscle

Agonist muscle.

antigravity muscles

Muscles that pull against gravity to maintain normal posture.
Synonym: postural muscles

appendicular muscle

One of the skeletal muscles of the limbs.

arrector pili muscle

Arrector pili.

arm muscle

Arm: biceps brachii, brachialis, coracobrachialis, and triceps muscles. Forearm, anterior: flexor carpi radialis, flexor carpi ulnaris, flexor digitorum profundus, flexor digitorum superficialis, flexor pollicis longus, and pronator quadratus muscles. Forearm, posterior: abductor pollicis longus, anconeus, brachioradialis, extensor carpi radialis brevis, extensor carpi radialis longus, extensor carpi ulnaris, extensor digitorum, extensor digitorum minimi, extensor indicis, extensor pollicis brevis, extensor pollicis longus, and supinator muscles.
See: arm for illus. (Muscles of the Arm)

articular muscle

A muscle attached to the capsule of a joint.

arytenoid muscle

The oblique or the transverse arytenoid -- laryngeal muscles. Origins: arytenoid cartilage. Insertions: contralateral arytenoid cartilage. Nerve: recurrent laryngeal and superior laryngeal of the vagus (CN X). Action: closes laryngeal inlet by bringing arytenoid cartilages toward each other.

auditory muscles

The tensor tympani and stapedius muscles.

axial muscle

A skeletal muscle that moves or stabilizes the head or the trunk.

back muscle

Superficial: latissimus dorsi and trapezius muscles. Middle layer: levator scapulae, rhomboid major, and rhomboid minor muscles. Deep layer: erector spinae and splenius. Deepest layer: interspinalis, intertransverse, multifidus, rotatores, semispinalis, and spinalis capitis.

biceps brachii muscle

Arm muscle. Origin: supraglenoid tubercle, coracoid process of scapula. Insertion: tuberosity of radius, posterior border of ulna (via bicipital aponeurosis). Nerve: musculocutaneous (C5-C6). Action: flexes forearm, supinates hand.
See: arm for illus. (Muscles of the Arm)

biceps femoris muscle

Leg muscle. Origin: ischial tuberosity, linea aspera and second supracondylar ridge of femur. Insertion: lateral condyle of tibia, head of fibula. Nerve: sciatic (L5-S2). Action: flexes leg, rotates leg laterally, extends thigh.
See: leg for illus. (Muscles of the leg)

bipennate muscle

A muscle in which the fibers converge from both sides to a central tendon.
illustration

brachialis muscle

Arm muscle. Origin: anterior surface of lower (distal) humerus. Insertion: coronoid process of ulna. Nerve: musculocutaneous and radial (C5-C7). Action: flexes forearm.
See: arm for illus. (Muscles of the Arm)

brachioradialis muscle

Arm muscle. Origin: lateral supracondylar ridge of distal humerus. Insertion: distal end of radius. Nerve: radial (C5-C7). Action: flexes forearm.
See: arm for illus. (Muscles of the Arm)

buccinator muscle

Facial muscle. Origin: pterygomandibular raphe and alveolar processes of jaws. Insertion: orbicularis oris muscle at angle of mouth. Nerve: facial (CN VII). Action: compresses check against teeth, retracts angle of mouth.

cardiac muscle

A tissue composed of mitochondrion-filled muscle cells that also contain neatly packed actin and myosin filaments; the filaments are arranged in cylindrical bundles called myofibrils. In each cell, the myofibrils are all aligned in the same direction and are parceled into longitudinal blocks (called sarcomeres) of similar lengths. Under the microscope, the ends of the blocks appear as lines, making cardiac muscle cells appear to have regularly arranged striations. In the muscle tissue, the cardiac muscle cells are connected in branching networks.

Cardiac muscle is innervated by both sympathetic and parasympathetic autonomic motor axons. In addition, cardiac muscle: is stimulated by blood—borne molecules, can conduct electrical impulses from cell to cell, and can independently generate rhythmical contractions. Cardiac muscle, which is found only in the heart, cannot be controlled consciously.

See: table

chest wall muscle

Pectoralis major, pectoralis minor, serratus anterior, subclavius, subscapularis, or teres major muscle.

chewing muscle

Mastication muscle.

ciliary muscle

Internal eye muscle. Origin: edges of sclera. Insertion: ciliary process of lens. Nerve: oculomotor (CN III). Action: allows lens to become more curved to focus on near objects.

constrictor muscle of pharynx

A muscle that constricts the pharynx; it is important for swallowing.

core muscle

One of the major muscles that stabilizes and controls the pressure inside the trunk; these are the pelvic floor, abdominal wall, back, and diaphragm muscles.

corrugator muscle

Facial muscle. Origin: medial part of supraorbital margin. Insertion: skin above middle of eyebrow. Nerve: facial (CN VII). Action: pulls eyebrows toward midline and downward.
Synonym: Corrugator supercilii

cremaster muscle

Spermatic cord muscle. Origin: inguinal ligament and pubic tubercle. Insertion: cremasteric fascia covering spermatic cord. Nerve: genitofemoral (L1-L2). Action: elevates testis in males.
See: penis for illus.

cricoarytenoid muscle

The lateral or the posterior cricoarytenoid -- laryngeal muscles. Origin: cricoid cartilage. Insertion: muscular process of arytenoid cartilage. Nerve: recurrent laryngeal of the vagus (CN X). Action: rotates arytenoid cartilages for vocalizations.

cricothyroid muscle

Laryngeal muscle. Origin: cricoid cartilage. Insertion: lower edges of thyroid cartilage. Nerve: superior laryngeal of the vagus (CN X). Action: tenses (stretches) vocal cords
See: thyroidfor illus.

deep neck muscle

One of the various neck muscles that surround the vertebral column and base of the skull and which are contained in the prevertebral cylinder of deep cervical fascia. All these muscles are innervated by cervical spinal nerves, and most of these muscles act primarily to move and stabilize the head.

deltoid muscle

Shoulder muscle. Origin: a bony ellipse from the lateral third of the clavicle over the acromial process and along the spine of the scapula. Insertion: deltoid tuberosity on the lateral shaft of the humerus. Nerve: axillary (C5-C6). Action: abducts arm.
See: arm for illus. (Muscles of the Arm)

detrusor muscle

The three-layered muscular wall of the urinary bladder. Nerve: primarily parasympathetic (S2-S4), secondarily sympathetic (T11-L2). Action: empties bladder.

diaphragm muscle

Origin: internal surfaces of lower six ribs, xiphoid process, vertebral bodies L1-L3. Insertion: central tendon (of diaphragm). Nerve: phrenic, lower six intercostals. Action: inflates lungs

digastric muscle

Neck muscle with two bellies. Origin: anterior belly attaches to the digastric fossa in mandible at base of anterior midline, posterior belly attaches to mastoid process. Insertion: tendon connecting both bellies in a loop of fascia that is attached to hyoid bone. Nerve: anterior belly -- trigeminal (CN V), posterior belly -- facial (CN VII). Action: lowers mandible and raises hyoid bone.
See: neck for illus.

erector spinae muscle

Three adjacent vertical bands of deep back muscles -- the iliocostalis, longissimus, and spinalis muscles. Origins: a wide tendon running along the iliac crest to the sacrum, the lower lumbar and sacral spinous processes. Insertions: along the back in the angles of the lower ribs, transverse processes of the thoracic and cervical vertebrae. Nerves: dorsal rami of the spinal nerves. Actions: extends (bends backward) the vertebral column and neck, twists the back.

extensor carpi ulnaris muscle

Forearm muscle. Origin: lateral epicondyle of humerus, proximal edge of ulna. Insertion: proximal end of fifth metacarpal. Nerve: radial (C7-C8). Action: adducts hand, extends wrist.
See: arm for illus. (Muscles of the Arm)

extensor digitorum muscle

Forearm muscle. Origin: lateral epicondyle of humerus. Insertion: common extensor tendon of fingers. Nerve: radial (C7-C8). Action: extends fingers and wrist.
See: arm for illus. (Muscles of the Arm)

extensor digitorum brevis muscle

Foot muscle. Origin: dorsolateral surface of calcaneus. Insertion: extensor tendons of toes. Nerve: deep peroneal (S1-S2). Action: extends toes.
See: leg for illus. (Muscles of the leg)

extensor digitorum longus muscle

Foot muscle. Origin: lateral condyle of tibia, upper three-fourths of fibula. Insertion: extensor tendons of toes 2-5. Nerve: deep peroneal (L5-S1). Action: extends toes, dorsiflexes foot.
See: leg for illus. (Muscles of the leg)

extensor hallucis longus muscle

Foot muscle. Origin: middle of fibula. Insertion: base of proximal phalanx of big toe. Nerve: deep peroneal (S1-S2). Action: dorsiflexes big toe.
See: leg for illus. (Muscles of the leg)

external intercostal muscles

The outer layer of muscles between the ribs, originating on the lower margin of each rib and inserted on the upper margin of the next rib. During inspiration, they draw adjacent ribs together, pulling them upward and outward, and increasing the volume of the chest cavity. They are controlled by the intercostal nerves.

external oblique muscle

Abdominal wall muscle. Origin: lower costal margin. Insertion: anterior half of iliac crest, rectus sheath, inguinal ligament. Nerve: intercostals 8-12, iliohypogastric, ilioinguinal (L1). Action: tenses and compresses abdomen, flexes and laterally rotates spine, lowers rib cage.

external pterygoid muscle

Lateral pterygoid muscle.

extraocular muscle

Abbreviation: EOM
Six muscles that attach outside the eyeball and that move the eye in its socket. The EOM are: the inferior and superior oblique muscles, and the lateral, medial, inferior, and superior rectus muscles.
See: extraocular for illus.

extrinsic muscle

Abbreviation: EM
The muscles outside an organ that control its position, such as the EM of the eye or tongue.

muscles of facial expression

Thin muscles that insert into the skin of the face; all are innervated by the facial nerve (CN VII). Scalp: frontalis and occipitalis muscles. Ear: anterior, posterior, and superior auricular muscles. Eye: orbicularis oculi. Nose: depressor septi, nasalis, and procerus muscles. Mouth: buccinator, depressor anguli oris, depressor labii inferioris, levator anguli oris, levator labii superioris, mentalis, orbicularis oris, risorius, and zygomaticus muscle. Neck: platysma.
See: face and headfor illus.

muscles of facial expression

Facial muscles.

fibularis muscles

The newer name for the peroneus muscles.

fibularis longus muscle

Peroneus longus muscle.

fixation muscle

A muscle that steadies a part so that more precise movements in a related structure may be accomplished.

flexor carpi radialis muscle

Forearm muscle. Origin: medial epicondyle of humerus. Insertion: bases of second and third metacarpals. Nerve: median (C6-C7). Action: abducts hand, flexes wrist.
See: Arm, muscles of the arm (illus.)

flexor carpi ulnaris muscle

Forearm muscle. Origin: medial epicondyle of humerus, medial side of olecranon, proximal posterior edge of ulna. Insertion: pisiform, hamate, and base of fifth metacarpal. Nerve: ulnar (C7-C8). Action: adducts hand, flexes wrist.

flexor digitorum longus muscle

Foot muscle. Origin: posterior surface of middle tibia. Insertion: distal phalanges of toes 2-5. Nerve: tibial (S2-S3). Action: flexes toes 2-5, plantarflexes foot.
See: leg for illus. (Muscles of the leg)

flexor digitorum profundus muscle

Forearm muscle. Origin: proximal three-fourths of ulna. Insertion: distal phalanges of fingers (digits 2-5). Nerve: ulnar, median (C8-T1). Action: flexes distal finger joints, aids in wrist flexion.

flexor digitorum superficialis muscle

Forearm muscle. Origin: medial epicondyle of humerus, coronoid process of ulna. Insertion: middle phalanges of fingers (digits 2-5). Nerve: median (C7-T1). Action: flexes fingers and wrist.
See: arm for illus. (Muscles of the Arm)

flexor hallucis longus muscle

Foot muscle. Origin: distal two-thirds of posterior tibia. Insertion: plantar side of distal phalanx of big toe. Nerve: tibial (S2-S3). Action: flexes big toe, plantarflexes foot.

flexor pollicis brevis muscle

A muscle of the hand originating on the flexor retinaculum and trapezium, trapezoid, and capitate and inserted on the lateral side of the base of the first phalanx of the thumb. It flexes the thumb at both the carpometacarpal joint and the metacarpophalangeal joint and is controlled by the median and the ulnar nerves.

flexor pollicis longus muscle

Forearm muscle. Origin: coronoid process of ulna, anterior surface of radius. Insertion: distal phalanx of thumb. Nerve: median (C8-T1). Action: flexes thumb.
See: arm for illus. (Muscles of the Arm)

foot muscles

Dorsal: dorsal interosseous, extensor digitorum brevis, extensor digitorum longus, extensor hallucis longus, and tibialis anterior muscles. Plantar: abductor digiti minimi, abductor hallucis, adductor hallucis, flexor digitorum brevis, flexor digiti minimi brevis, flexor hallucis brevis, lumbrical, plantar interosseous, and quadratus plantae muscles.
See: leg for illus. (Muscles of the leg)

frontalis muscle

Front half of occipitofrontalis muscle – a facial muscle. Origin: epicranial (scalp) aponeurosis. Insertion: skin of eyebrows, root of nose. Nerve: facial (CN VII). Action: elevates eyebrows, wrinkles forehead.
See: face and head for illus.

fusiform muscle

A muscle resembling a spindle. See: bipennate muscle for illus.

gastrocnemius muscle

Leg muscle. Origin: medial condyle of femur, lateral condyle of femur. Insertion: calcaneus (via Achilles tendon). Nerve: tibial (S1-S2). Action: plantarflexes foot, flexes knee.
See: leg for illus. (Muscles of the leg)

gemellus muscle

Either of the two muscles that attach to the medial surface of the greater trochanter of the femur (the trochanteric fossa) where they mesh with the tendon of the obturator internus muscle. The superior gemellus muscle arises from the ischial spine and is innervated by the nerve to the obturator internus; the inferior arises from the ischial tuberosity and is innervated by the femoral nerve. Both muscles hold the head of the femur in the acetabulum, rotate (laterally) the thigh in extension, and abduct the thigh when it is flexed.

genioglossus muscle

Tongue muscle. Origin: genial tubercle on inside of mandibular symphysis. Insertion: ventral tongue, hyoid bone. Nerve: hypoglossal (CN XII). Action: protrudes and depresses tongue.

gluteus maximus muscle

Thigh muscle. Origin: upper outer edge of ilium and sacrum. Insertion: iliotibial tract of fascia lata, gluteal tuberosity of femur. Nerve: inferior gluteal (L5-S2). Action: extends, abducts, and laterally rotates thigh.

gluteus medius muscle

Thigh muscle. Origin: lower half of ilium. Insertion: proximal medial tibia. Nerve: obturator (L2-L3). Action: adducts, flexes, and medially rotates thigh.

gracilis muscle

Thigh muscle. Origin: lower half of pubis. Insertion: proximal medial tibia. Nerve: obturator (L2-L3). Action: adducts, flexes, and medially rotates thigh.
See: leg for illus. (Muscles of the leg)

hamstring muscles

Posterior thigh muscles that originate on the ischial tuberosity and act across both the hip and knee joints; they are the biceps femoris, gracilis, sartorius, semitendinosus, and semimembranosus muscles.

hand muscles

Abductor digiti minimi, abductor pollicis brevis, adductor pollicis, dorsal interosseous, flexor digiti minimi, flexor pollicis brevis, lumbrical, opponens digiti minimi, opponens pollicis, palmaris brevis, and palmar interosseous muscles.

Hilton muscle

See: Hilton, John

hyoglossus muscle

A sheet of muscle extending up from the hyoid bone to the ipsilateral base and sides of the tongue. It depresses the sides of the tongue and is innervated by cranial nerve XII (hypoglossal nerve).

iliacus muscle

Thigh muscle. Origin: iliac fossa. Insertion: lesser trochanter of femur, psoas major tendon. Nerve: femoral (L2-L3). Action: flexes thigh.

iliopsoas muscle

The iliacus and psoas major muscles considered together.
See: leg for illus. (Muscles of the leg)

inferior oblique muscle

Extraocular muscle. Origin: inside front lower margin of maxillary part of orbit. Insertion: lateral surface of eyeball behind its equator. Nerve: oculomotor (CN III). Action: turns eye up and outward with lateral rotation.
See: extraocular for illus.

inferior rectus muscle

Extraocular muscle. Origin: tendinous ring around optic nerve at rear of orbit. Insertion: lower edge of eyeball in front of its equator. Nerve: oculomotor (CN III). Action: turns eye down and medially.
See: extraocular for illus.

infraspinatus muscle

Shoulder muscle. Origin: medial two-thirds of infraspinatus fossa of scapula. Insertion: posterior side of greater tubercle of humerus. Nerve: suprascapular (C4-C6). Action: rotates arm laterally.

internal intercostal muscles

The muscles between the ribs, lying beneath the external intercostals. During expiration, they pull the ribs downward and inward, decreasing the volume of the chest cavity and contributing to a forced exhalation.

internal pterygoid muscle

Medial pterygoid muscle.

intrinsic muscle

A muscle that has both its origin and insertion within a structure, as intrinsic muscles of the tongue, eye, hand, or foot.

involuntary muscle

A muscle not under conscious control: smooth, cardiac, and some skeletal muscles.

laryngeal muscle

Any of six short muscles inside the larynx that move the vocal apparatus and (except for the cricothyroid muscle) are innervated by the recurrent laryngeal branch of the vagus nerve (CN X).

lateral pterygoid muscle

One of the mastication muscles. Origin: greater wing of sphenoid bone, lateral pterygoid plate. Insertion: pterygoid fovea of condyle of mandible. Nerve: trigeminal (CN V). Action: opens mouth, protrudes mandible.
Synonym: external pterygoid muscle See: arm for illus.

lateral rectus muscle

Extraocular muscle. Origin: tendinous ring around optic nerve at rear of orbit. Insertion: temporal edge of eyeball in front of its equator. Nerve: abducens (CN VI). Action: turns eye laterally.
See: extraocular for illus.

latissimus dorsi muscle

Back muscle. Origin: spinous processes of vertebrae T7-S3, thoracolumbar fascia, iliac crest. Insertion: bicipital groove of humerus. Nerve: thoracodorsal (C6-C8). Action: adducts, extends, and medially rotates arm.

leg muscles

Anterior and lateral: extensor digitorum longus, extensor hallucis longus, peroneus, peroneus longus, peroneus tertius, and tibialis anterior muscles. Posterior: flexor digitorum longus, flexor hallucis longus, gastrocnemius, plantaris, popliteus, soleus, and tibialis posterior muscles.
See: leg for illus. (Muscles of the leg)

levator ani muscle

The set of pelvic floor muscles, which include the iliococcygeus, levator prostatae or vaginal sphincter, pubococcygeus, and puborectalis muscles. Origins: insides of pelvic bones (pubis, arcus tendinaeus, ischial spine, and sacrospinous ligament). Insertions: perineal body, coccyx, anococcygeal ligament, lower sacrum. Nerve: perineal of spinal S4, pudendal. Action: supports pelvic viscera, contributes to urethral, vaginal, and anal sphincter actions.

levator palpebrae muscle

Eyelid muscle. Origin: inner roof of orbit. Insertion: skin and tarsal plate of upper eyelid. Nerve: oculomotor (CN III). Action: raises upper eyelid.
See: extraocular for illus.

lumbrical muscle

Hand and foot muscles. Origins: tendons of flexor digitorum profundus or flexor digitorum longus. Insertions: extensor tendons of digits 2-5. Nerve, hand: median (C8-T1), ulnar (C8-T1). Nerve, foot: medial plantar (S2-S3), lateral plantar (S2-S3). Action: flex the straightened digits (specifically, flex the metacarpophalangeal or metatarsophalangeal joints while extending the interphalangeal joints).

masseter muscle

Muscle of mastication. Origin: zygomatic process of maxilla, zygomatic arch. Insertion: coronoid process, lower half of ramus, and angle of mandible. Nerve: trigeminal (CN V). Action: elevates mandible to close jaw.
See: headfor illus.

mastication muscle

The chewing muscle, which is innervated by the mandibular division of the trigeminal nerve (CN V). These muscles include the masseter, temporalis, and medial and lateral pterygoid muscles. Synonym: chewing muscle

medial pterygoid muscle

Muscle of mastication. Origin: lateral pterygoid plate. Insertion: medial surface of ramus and angle of mandible. Nerve: trigeminal (CN V). Action: closes mouth, protrudes mouth, moves jaw sideways.
Synonym: internal pterygoid muscle

medial rectus muscle

Extraocular muscle. Origin: tendinous ring around optic nerve at rear of orbit. Insertion: nasal edge of eyeball in front of its equator. Nerve: oculomotor (CN III). Action: turns eye medially.

mentalis muscle

Facial muscle. Origin: incisive fossa at front of mandible. Insertion: skin of chin. Nerve: facial (CN VII). Action: raises and protrudes lower lip.
See: face and headfor illus.

mimetic muscles

Facial muscles. Synonym: muscles of facial expression

multipennate muscle

A muscle with several tendons of origin and several tendons of insertion, in which fibers pass obliquely from a tendon of origin to a tendon of insertion on each side. See: bipennate muscle for illus.

mylohyoid muscle

Neck muscle. Origin: mylohyoid line of mandible. Insertion: hyoid bone, mylohyoid raphe. Nerve: trigeminal (CN V). Action: elevates hyoid and larynx, lowers jaw.

nasalis muscle.

The major nose muscle and a muscle of facial expression.

neck muscles

Anterior and lateral: digastric, geniohyoid, mylohyoid, omohyoid, platysma, sternocleidomastoid, sternohyoid, sternothyroid, stylohyoid, and thyrohyoid muscles. Posterior: levator scapulae, scalene muscles, and trapezius. Suboccipital: obliquus capitis and rectus capitis muscles.
See: headfor illus.

nonstriated muscle

Smooth muscle.

obturator muscle

Either of the two muscles on each side of the pelvic region that rotate the thighs outward.

opponens pollicis muscle

A muscle of the hand originating on the trapezium and flexor retinaculum and inserted in the first metacarpal. It flexes and adducts the thumb (brings it across the palm) and is controlled by the median nerve.

orbicular muscle

A muscle encircling an opening.

orbicularis oculi muscle

Facial muscle. Origin: completely surrounds eye, attaches to medial palpebral ligament (and adjacent bones) and lacrimal crest (and adjacent bones). Insertion: medial palpebral raphe (after encircling orbit), lateral palpebral raphe, tarsi of eyelids. Nerve: facial (CN VII) Action: closes eyelids, lifts cheeks, compresses lacrimal sac.
See: face and headfor illus.

orbicularis oris muscle

Facial muscle. Origin: adjacent facial muscles that surround mouth. Insertion: into itself and skin of lips while encircling mouth. Nerve: facial (CN VII). Action: closes and purses lips.
See: face and headfor illus.

muscles of the palate

Levator veli palatini, musculus uvulae, palatoglossus, palatopharyngeus, pharyngeal constrictor, salpingopharyngeus, and tensor veli palatine muscles.

palmaris longus muscle

Forearm muscle. Origin: medial epicondyle of humerus. Insertion: palmar surface of flexor retinaculum, palmar aponeurosis. Nerve: median (C7-C8). Action: flexes hand.
See: arm for illus. (Muscles of the Arm)

papillary muscle

Internal conical heart muscles. Origin: ventricular wall. Insertion: tricuspid and mitral valve leaflets via chordae tendinae. Action: anchor leaflets of valves during heart contractions.

pectinate muscle

A ridge of myocardium on the inner wall of either atrium of the heart.

pectoralis major muscle

Chest wall muscle. Origin: medial half of clavicle, sternum, costal cartilages 4-6. Insertion: lateral edge of bicipital groove of humerus. Nerve: lateral and medial pectoral (C5-T1). Action: adducts and medially rotates arm.

pectoralis minor muscle

Chest wall muscle. Origin: Anterior medial surface of ribs 3-5. Insertion: coracoid process of scapula. Nerve: lateral and medial pectoral (C6-C8). Action: pulls shoulder forward and down, elevates rib cage.

peroneus longus muscle

Leg muscle. Origin: lateral two-thirds of fibula. Insertion: medial cuneiform bone, base of first metatarsal. Nerve: superficial peroneal (L5-S1). Action: everts and plantar flexes foot.
Synonym: fibularis longus muscle See: leg for illus. (Muscles of the leg)

pharynx and tongue muscles

Cricothyroid, genioglossus, geniohyoid, hyoglossus, palatoglossus, pharyngeal constrictor, styloglossus, stylopharyngeus, salpingopharyngeus, and thyrohyoid muscles.

piriformis muscle

Thigh muscle. Origin: anterior surface of sacrum. Insertion: upper part of greater trochanter of femur. Nerve: spinal L5-S2. Action: laterally rotates thigh.

platysma muscle

Neck and facial muscle. Origin: superficial fascia of upper chest. Insertion: skin of lower face. Nerve: facial (CN VII). Action: lowers jaw, widens neck.
See: face and headfor illus.

postaxial muscle

A muscle on the posterior or dorsal aspect of a limb.

postural muscles

Antigravity muscles.

preaxial muscle

A muscle on the anterior or ventral aspect of a limb.

procerus muscle

A muscle that arises in the skin over the nose and is connected to the forehead. It acts to draw the eyebrows down.

pronator teres muscle

Arm muscle. Origin: medial epicondyle of humerus, coronoid process of ulna. Insertion: lateral side of middle of radius. Nerve: median (C6-C7). Action: pronates forearm.

psoas major muscle

Thigh muscle. Origin: bodies of vertebrae T12-L1. Insertion: lesser trochanter of femur. Nerve: lumbar L1-L3. Action: flexes thigh.

pterygoid muscle

The lateral or the medial pterygoid muscle.

puborectalis muscle

Pelvic muscle, part of levator ani. Origin: back surface of pubis. Insertion: joins other levator ani muscles forming a bowl shaped diaphragm, encircles anal canal, and attaches to sacrum and coccyx. Nerve: inferior rectal and sacral (S4). Action: supports pelvis, holds anal canal at right angle to rectum.

quadriceps muscle

The rectus femoris, vastus intermedius, vastus lateralis, and vastus medius muscles together.

rectus abdominis muscle

Abdominal wall muscle. Origin: crest and symphysis of pubis. Insertion: xiphoid process, costal cartilages 5-7. Nerve: spinal T7-T12. Action: tenses abdomen, flexes vertebral column.

rectus femoris muscle

Thigh muscle. Origin: anterior inferior iliac spine, upper edge of acetabulum. Insertion: tibial tuberosity (via the patellar ligament). Nerve: femoral (L2-L4). Action: extends leg, flexes thigh.
See: leg for illus. (Muscles of the leg)

red muscle

Twitch skeletal muscle cells containing myoglobin and many mitochondria. These cells largely generate energy via aerobic oxidation and are suited for maintaining contractions for an extended time.

muscle of respiration

Any of the muscles used in breathing, including the diaphragm, the muscles of the rib cage, and the abdominal muscles. See: diaphragm; expiration; inspiration

rhomboid muscle

The major or the minor rhomboid muscle -- shoulder muscles. Origins: nuchal ligament, spinous processes of vertebrae C7-T5. Insertion: vertebral edge of scapula. Nerve: dorsal scapular (C4-C5). Action: pulls scapulae toward each other.
See: illus. (Muscles of the Trunk)

rotator cuff muscles

Shoulder muscles -- the infraspinatus, subscapularis, supraspinatus, and teres minor muscles -- which hold the head of the humerus in the glenoid fossa of the scapula.

sartorius muscle

Thigh muscle. Origin: anterior superior iliac spine. Insertion: medial side of proximal tibia. Nerve: femoral (L2-L3). Action: flexes thigh and leg, laterally rotates thigh.
See: leg for illus. (Muscles of the leg)

scalene muscle

The anterior, the middle, or the posterior scalene muscle -- neck muscles. Origins: transverse processes of vertebrae C1-C7. Insertions: upper surfaces of ribs 1-2. Nerves: cervical spinal C4-C8. Actions: raises ribs 1-2, bends neck ipsilaterally.

semimembranosus muscle

Thigh muscle. Origin: ischial tuberosity. Insertion: medial condyle of tibia. Nerve: sciatic (L5-S2). Action: extends thigh, flexes and medially rotates leg.
See: leg for illus. (Muscles of the leg)

semitendinosus muscle

Thigh muscle. Origin: ischial tuberosity. Insertion: upper medial tibia near tuberosity. Nerve: sciatic L5-S2). Action: extends thigh, flexes and medially rotates leg.
See: leg for illus. (Muscles of the leg)

serratus muscle

Any of several muscles arising from the ribs or vertebrae by separate slips.

serratus anterior muscle

Chest muscle. Origin: outer surface of ribs 1-8. Insertion: anterior side of vertebral edge of scapula. Nerve: long thoracic (C5-C7). Action: pulls scapula forward (anterior) and laterally (abduction), rotates scapula upward.

shoulder muscles

Deltoid, infraspinatus, subscapularis, supraspinatus, teres major and teres minor muscles.
Enlarge picture
MORPHOLOGICAL FORMS OF MUSCLE
Enlarge picture
MORPHOLOGICAL FORMS OF MUSCLE
Enlarge picture
MORPHOLOGICAL FORMS OF MUSCLE

skeletal muscle

A tissue composed of muscle cells (often multinucleated) that contain neatly packed actin and myosin filaments; these filaments are arranged in cylindrical bundles called myofibrils. In each cell, the myofibrils are all aligned in the same direction and are parceled into longitudinal blocks (called sarcomeres) of similar lengths. Under the microscope, the ends of the blocks look like lines, making skeletal muscle cells appear to have regularly arranged striations. See: illustration

Skeletal muscle is innervated by somatic (as opposed to autonomic) motor axons at a synaptic structure called a motor endplate, where acetylcholine is the neurotransmitter. Most skeletal muscles can be controlled consciously, and skeletal muscle is sometimes referred to as voluntary muscle. Skeletal muscle cells contract more forcefully than smooth or cardiac muscle cells.

Skeletal muscle got its name because it usually attaches at one end to bone. Skeletal muscle is by far the most common type of muscle in the body and it plays a major role in normal metabolism, e.g., after a meal, excess glucose is removed from the blood stream primarily by skeletal muscle.

smooth muscle

A tissue composed of muscle cells that contain loosely-organized actin and myosin filaments. The lack of tight organization means that smooth muscle cells do not appear striated when examined under a microscope. Smooth muscle tissue tends to occur as sheets and is typically found in the walls of tubes, e.g., arteries, and sacs, e.g., the gastrointestinal system.

Smooth muscles are innervated by both sympathetic and parasympathetic autonomic motor axons; they are also stimulated by blood-borne molecules. Smooth muscles cannot be consciously controlled, and this form of muscle tissue is called involuntary muscle. Smooth muscle cells contract more slowly than skeletal or cardiac muscle cells.

Synonym: nonstriated muscle.; unstriated muscle. See: table

soleus

Leg muscle. Origin: proximal ends of tibia and fibula. Insertion: calcaneus via Achilles tendon. Nerve: tibial (S1-S2). Action: plantarflexes foot.
See: leg for illus. (Muscles of the leg)

somatic muscle

Muscle derived from mesodermal somites, including most skeletal muscle.

sphincter muscle

A muscle that encircles a duct, tube, or orifice, thus controlling its opening.

sphincter muscle of urinary bladder

The smooth muscle fibers around the origin of the urethra. Contraction of this muscle prevents urination; relaxation permits it.

stabilizer muscle

A muscle that supports a body segment so muscles attached to it can function.

stapedius muscle

Middle ear muscle. Origin: posterior wall of middle ear. Insertion: neck of stapes. Nerve: facial (CN VII). Action: tilts stapes, dampens excessive vibrations.

sternocleidomastoid muscle

Neck muscle. Origin: upper edge of manubrium, middle of upper clavicle. Insertion: mastoid process. Nerve: accessory (CN XI), spinal C2. Action: contralaterally rotates head.
See: face and headfor illus.

striated muscle

See: table

subscapularis muscle

Shoulder muscle. Origin: medial subscapular fossa. Insertion: lesser tubercle of humerus. Nerve: upper and lower subscapular (C5-C7). Action: medially rotates arm.

superior oblique muscle

Extraocular muscle. Origin: sphenoid bone deep in medial side of orbit. Insertion: lateral surface of eyeball behind its equator. Nerve: trochlear (CN IV). Action: turns eye down and outward with medial rotation.

superior rectus muscle

Extraocular muscle. Origin: tendinous ring around optic nerve at rear of orbit. Insertion: upper edge of eyeball in front of its equator. Nerve: oculomotor (CN III). Action: turns eye up and medially.
See: extraocular for illus.

supraspinatus muscle

Shoulder muscle. Origin: medial supraspinous fossa of scapula. Insertion: greater tubercle of humerus. Nerve: suprascapular (C4-C6). Action: abducts arm.

synergistic muscles

Muscles aiding one another in function.

temporalis muscle

Muscle of mastication. Origin: temporal fossa of skull. Insertion: coronoid process of mandible. Nerve: trigeminal (CN V). Action: closes mouth, clenches teeth, retracts jaw.
See: headfor illus.

tensor fascia lata muscle

Thigh muscle. Origin: iliac crest, anterior superior iliac spine. Insertion: iliotibial tract of fascia lata. Nerve: superior gluteal (L4-L5). Action: stabilizes (abducts) thigh, extends and laterally rotates leg.

tensor tympani muscle

Middle ear muscle. Origin: wall of auditory tube. Insertion: handle of malleus. Nerve: trigeminal (CN V). Action: tenses tympanic membrane, dampens excessive vibrations.

teres major muscle

Shoulder muscle. Origin: lower lateral edge of scapula. Insertion: bicipital groove of humerus. Nerve: lower scapular (C6-C7). Action: adducts and medially rotates arm.

teres minor muscle

Shoulder muscle. Origin: upper lateral edge of scapula. Insertion: greater tubercle of humerus. Nerve: axillary (C4-C6). Action: laterally rotates arm.

thenar muscle

The abductor or flexor muscle of the thumb.

thigh muscles

Anterior: iliopsoas, quadriceps (rectus femoris, vastus intermedius, vastus lateralis, and vastus medius), and sartorius muscles. Medial: adductor brevis, adductor longus, adductor magnus, gracilis, and pectineus muscles. Gluteal region: gemelli, gluteus maximus, gluteus medius, gluteus minimus, obturator externus, obturator, internus, piriformis, quadratus femoris, and tensor fasciae lata muscles. Posterior: biceps femoris, semimembranosus, and semitendinosus muscles.
See: leg for illus. (Muscles of the leg)

thyroepiglottic muscle

A muscle arising on the inner surface of the thyroid cartilage. It extends upward and backward and is inserted on the epiglottis. It depresses the epiglottis.

tibialis anterior muscle

Leg muscle. Origin: lateral side of proximal tibia. Insertion: medial side of cuneiform bone, base of metatarsal 1. Nerve: deep peroneal (L4-L5). Action: inverts and dorsiflexes foot.

tibialis posterior muscle

Leg muscle. Origin: anterior tibia and fibula. Insertion: navicular, cuneiform, and cuboid bones; metatarsals 2-4. Nerve: tibial (L4-L5). Action: inverts and plantarflexes foot.

tonic muscle

Skeletal muscle fibers that contract slowly and that cannot propagate an action potential along their cell membranes. Tonic muscles are uncommon in humans and are found only in the extraocular muscles, stapedius muscle, and intrafusal fibers of the muscle spindles. The remainder of human skeletal muscle contains only twitch fibers.

trapezius muscle

Neck and back muscle. Origin: occipital bone (superior nuchal line), nuchal ligament, spinous processes of vertebrae C7-T12. Insertion: posterior edge of lateral clavicle, acromion, posterior edge of spine of scapula. Nerve: accessory (CN XI), spinal C3-C4. Action: elevates, retracts, and rotates scapula.
See: face and headfor illus.

triangular muscle

A flat muscle with a broad origin and narrow insertion.

triceps muscle

Arm muscle. Origin: infraglenoid tubercle of scapula, posterior of proximal humerus, posterior of distal humerus. Insertion: olecranon process. Nerve: radial (C6-C8). Action: extends forearm.
Synonym: triceps brachii muscle See: arm for illus. (Muscles of the Arm)

triceps brachii muscle

Triceps muscle.

tricipital muscle

A muscle with three tendons of origin and a single, common insertion.

twitch muscle

Muscle fibers that can conduct axon potentials along their cell membranes. Almost all skeletal muscle in humans is twitch muscle. A very small number of muscles in humans are tonic muscles. Twitch muscles cells can be categorized into a number of types on the basis of the biochemical cycle that they use to produce their energy: red (oxidative), white (glycolytic), or intermediate (oxidative/glycolytic). Most human muscles are composed of a mix of twitch muscle cell types.

unipennate muscle

A muscle whose fibers converge on only one side of a tendon. See: bipennate muscle for illus.

unstriated muscle

Smooth muscle.

uterine muscle

See: myometrium

vastus intermedius muscle

Thigh muscle. Origin: anterior and lateral sides of proximal femur. Insertion: common tendon of quadratus muscles, tibial tuberosity via patellar ligament. Nerve: femoral (L2-L4). Action: extends leg.

vastus lateralis muscle

Thigh muscle. Origin: lateral side of proximal femur. Insertion: common tendon of quadratus muscles, tibial tuberosity via patellar ligament. Nerve: femoral (L2-L4). Action: extends leg.
See: leg for illus. (Muscles of the leg)

vastus medialis muscle

Thigh muscle. Origin: medial side of femur Insertion: common tendon of quadratus muscles, tibial tuberosity via patellar ligament. Nerve: femoral (L2-L4). Action: extends leg.

vocalis muscle

Laryngeal muscle. Origin: midline of inner surface of thyroid cartilage. Insertion: arytenoid cartilage. Nerve: recurrent laryngeal of vagus (CN X). Action: changes tension of vocal cords.

voluntary muscle

A muscle that can be controlled voluntarily; most skeletal muscles are voluntary.
SmoothCardiacStriated
SynonymsInvoluntaryMyocardialVoluntary
NonstriatedSkeletal
Visceral
Fibers
Length (in/m)50–20025,000
Thickness (in/m) 4–8 75
ShapeSpindlesCylinders
MarkingsNo striationStriationMarked striation
NucleiSingleSingleMultiple
Effects of cutting related nerveSlightRegulation of heart rate is lostComplete paralysis
illustration

muscle

A tissue consisting of large numbers of parallel elongated cells with the power of shortening and thickening so as to approximate their ends and effect movement. Up to 50% of the body weight consists of muscle, most being attached to bone in such a way that muscle contraction causes joints to bend (flex) or straighten (extend). Muscle fibres convert chemical energy into mechanical energy. There are three kinds of muscle—striped (striated) or voluntary muscle; smooth or involuntary muscle occurring in the walls of arteries, the intestines and the urinary tract; and heart muscle (MYOCARDIUM), a network (syncytium) of muscle fibres that contract regularly and automatically without external stimulus.
Muscleclick for a larger image
Fig. 225 Muscle . A sarcomere.

muscle

the fleshy part of any animal that consists of tissue made up of highly contractile cells which serve to move parts of the body relative to each other.

A muscle is composed of many fibres or muscle cells. In STRIATED MUSCLE, each cell contains a bundle of MYOFIBRILS each exhibiting a banding pattern and being made up of a number of SARCOMERES arranged end to end. The sarcomere is the unit of contraction and the banding visible over its surface results from the longitudal filaments which make up the myofibril being of two types, thick (dark) and thin (light). These filaments overlap as shown in Fig. 225. The thick filaments are composed of the protein MYOSIN and the thin filaments of ACTIN. H.E. Huxley and K. Harrison found that on contraction, the light zones (I-BANDS) were comparatively narrow; on relaxation of the muscle the I-bands were broad. Where very strong contraction takes place the H-zone disappears and the thin filaments overlap.

Huxley and Harrison proposed the sliding filament hypothesis, to account for their observations. Bridges occur between thick and thin filaments and in contraction the bridges pull thin filaments past the thick ones using a ratchet mechanism. Some filaments are retained in this ‘pulled past’ position whilst others detach then reattach and repeat the ‘pulling past’ action. ACTOMYSIN is formed at the point of contact of bridge and thin filament. For each bridge to go through its cycle of attachment, contraction and reattachment, the splitting of one molecule of ATP is required, the cycles occurring between 50 and 100 times per second. The supply of ATP comes from MITOCHONDRIA between the fibrils. Calcium ions are released from vesicles in the sarcoplasmic reticulum, by the ACTION POTENTIAL passing along the surface of the fibre and these split the ATP. Troponin activated by the calcium displaces tropomyosin, which prevents myosin bridges from binding with actin fibrils. Once binding takes place this activates ATPase and on hydrolysis of ATP the bridge goes through its cycle of movement.

Figure 1: Muscles of the back.
Figure 2: Muscles of the abdominal wall. Superficial layer shown on the right side of the body, deeper layer on the left.
Figure 3: Muscles of the shoulder girdle and upper limb.
Figure 4: Muscles of the shoulder girdle and upper limb.
Figure 5: Muscles of the lower limb. Left leg from the front.
Figure 6: Muscles of the lower limb. Left leg from the back.
Figure 7: Structure of skeletal muscle at progressively higher magnification, from whole muscle to contractile proteins (A-D, F). E represents the 'sliding filaments' diagrammatically.

muscle

contractile soft tissue, responsible for all significant active movements and force-generations in an animal body. Divisible into three classes: (1) skeletal or voluntary muscle the class of muscle acting, in almost all body locations, to move one bone relative to another, the more superficial skeletal muscles being visible under the skin in all but the most obese subjects; (2) cardiac muscle the type unique to the heart; (3) smooth muscle composing the actively adjustable components of the walls of blood vessels and of the gastrointestinal, respiratory, urinary and reproductive tracts. Skeletal and cardiac are the striated muscles; cardiac and smooth share the property of being involuntary. See also muscle fibres, muscle fibre types, myofibrils; Figure 1, Figure 2, Figure 3, Figure 4, Figure 5, Figure 6, Figure 7.

muscle

fibrous contractile tissue, stimulation of which allows movement of body parts or alterations in function of various organs (see Table 1 and Table 2; muscular tissue; see named individual muscles)
Table 1: Muscles acting on the joints of the lower limb and foot
JointMuscleMuscle originMuscle insertion
Hip onlyAdductor longus
Adductor brevis
Adductor magnus
Psoas major
Iliacus
Pectineus
Gluteus minimus
Gluteus medius
Gluteus maximus (deep quarter)
Piriformis
Obturator externus
Obturator internus
Gemelli
Body of pubis
Body and inferior ramus of pubis
Inferior ramus of pubis
Lumbar vertebrae
Iliac fossa
Body and superior ramus of pubis
Ileum
Ileum
Sacrum
Sacrum
Obturator membrane
Internal surfaces of ileum, pubis
Ischium, sides of sciatic notch
Linea aspera of posterior femur
Linea aspera of posterior femur
Lower medial femur, adductor tubercle
Lesser trochanter
Femur, inferior to lesser trochanter
Posterior area of lesser trochanter
Anterior area greater trochanter
Lateral area greater trochanter
Gluteal tuberosity of femur
Greater trochanter
Trochanteric fossa
Medial area greater trochanter
Medial area greater trochanter
Hip and kneeBiceps femoris (long head)
Semimembranosus
Semitendinosus
Gracilis
Sartorius
Tensor fasciae lata
Rectus femoris
Gluteus maximus (superior three-quarters)
Ischial tuberosity
Ischial tuberosity
Ischial tuberosity
Body and inferior ramus of pubis
Anterior superior iliac spine
Anterior one-quarter of iliac crest
Anterior ileum
Posterior area of ileum and sacrum
Head of fibula
Posterior-area medial tibial condyle
Upper one-quarter medial tibia
Upper one-quarter medial tibia
Upper one-quarter medial tibia
Lateral condyle tibia via iliotibial tract
Patella, via quadriceps tendon
Lateral condyle tibia via iliotibial tract
Knee onlyVastus medialis
Vastus intermedius
Vastus lateralis
Biceps femoris (short head)
Popliteus
Anterior upper femur and tendon of adductor magnus
Anterior and lateral surfaces of body of femur
Greater trochanter and linea aspera of femur
Linea aspera
Lateral condyle of femur
Superior and medial surfaces of patella and capsule of knee joint
Superior surface of patella and suprapatellar bursa
Superior and lateral surfaces of patella and capsule of knee joint
Head of fibula
Posterior surface of upper tibia
Knee and ankleGastrocnemius
Plantaris
Lateral surface of lateral condyle and posterior surface of medial femoral condyle
Posterior surface of lateral femoral condyle
Calcaneum, via Achilles tendon
Calcaneum, via Achilles tendon (acts with gastrocnemius)
Ankle onlySoleusSoleal line and middle one-third of medial border of tibia and posterior surface of upper one-third fibulaCalcaneum, via Achilles tendon
Ankle and tarsusPeroneus longus
Peroneus brevis
Tibialis anterior
Tibialis posterior
Peroneus tertius
Lateral surface of upper two-thirds of lateral fibula
Lateral surface of lower two-thirds of lateral fibula
Lateral surface of upper one-half of tibia and local interosseous membrane
Upper one-half of tibia, fibula and local interosseous membrane
Anterior surface of distal one-quarter of fibula
Base of first metatarsal and lateral side of medial (first) cuneiform
Base of fifth metatarsal
Base of first metatarsal and inferomedial aspect of medial (first) cuneiform
Medial (first) cuneiform, inferior aspects of all tarsal bones (except the talus) and bases of second, third and fourth metatarsals
Dorsal shaft of fifth metatarsal
Tarsus and toesExtensor digitorum brevis
Flexor digitorum brevis
Flexor accessories (quadratus plantae)
Abductor hallucis
Abductor digiti minimi
Superior and anterior surfaces of the calcaneum
Medial process of calcaneal tuberosity
Plantar, medial and lateral aspects of calcaneum
Medial process of calcaneal tuberosity and flexor retinaculum
Calcaneal tuberosity
Dorsum of proximal phalanx of hallux, and extensor expansions of toes 2-4
Plantar, middle phalanges of toes 2-5
Tendon flexor digitorum longus
Medial side of proximal phalanx of hallux
Lateral side of proximal phalanx of fifth toe
Toes onlyDorsal interossei
Plantar interossei
Lumbricals
Flexor hallucis brevis
Adductor hallucis
Flexor digiti minimi brevis
Adjacent sides of metatarsals 1-5
Medial sides of metatarsals 3-5
Digital tendon slips of flexor digitorum longus
Medial plantar aspect of the cuboid
Bases of 2-4 metatarsals and transverse plantar ligament of 2-4 metatarsophalangeal joints
Base of fifth metatarsal
Lateral side of toes 2-4 and medial side toe 2
Medial sides of bases of proximal phalanges of toes 3-5
Extensor expansions toes 2-5
Medial and lateral sides of base of proximal phalanx of hallux
Lateral side of base of proximal side of hallux
Lateral side of base of proximal phalanx of toe 5
Table 2: Movements occurring about the joints of the lower limb and foot
Movement about jointMuscle causing the movementNerve supply to muscle
Hip flexionIliacus
Psoas major
Rectus femoris
Sartorius
Tensor fasciae lata
Pectineus
Adductor longus
Adductor brevis
Ventral rami of L1 and L2
Ventral rami of L1 and L2
Femoral
Femoral
Superior gluteal
Femoral
Obturator
Obturator
Hip extensionGluteus maximus
Semimembranosus
Semitendinosus
Biceps femoris, long head
Adductor magnus, ischial part
Inferior gluteal
Tibial part of sciatic nerve
Tibial part of sciatic nerve
Tibial part of sciatic nerve
Tibial part of sciatic nerve
Hip adductionAdductor longus
Adductor brevis
Adductor magnus
Gracilis
Pectineus
Quadratus femoris
Obturator
Obturator
Obturator
Obturator
Femoral
Ventral rami of L4, L5 and S1
Hip abductionGluteus medius
Gluteus minimus
Tensor fasciae lata
Piriformis
Obturator internus, in flexion
Superior gluteal
Superior gluteal
Superior gluteal
Ventral rami of L5 and SI
Ventral rami of L5 and S1
Medial rotation of leg at hipTensor fasciae lata
Gluteus minimus
Anterior fibres of gluteus maximus
Adductors longus, brevis and magnus
Iliopsoas
Superior gluteal
Superior gluteal
Superior gluteal
Superior gluteal
Ventral rami L1 and L2
Lateral rotation of leg at hipSartorius
Gluteus maximus
Obturator internus
Gemelli
Obturator externus
Quadratus femoris
Piriformis, in flexion
Femoral
Inferior gluteal
Ventral rami of L5, S1 and S2
Ventral rami of L5, S1 and S2
Obturator
Ventral rami of L4, L5 and S1 Ventral rami of L5, S1 and S2
Knee flexionSemimembranosus
Semitendinosus
Biceps femoris, long head
Biceps femoris, short head
Gracilis
Sartorius
Popliteus
Gastrocnemius
Sciatic (tibial)
Sciatic (tibial)
Sciatic (tibial)
Common peroneal
Obturator
Femoral
Tibial
Tibial
Knee extensionVastus medialis
Vastus lateralis
Vastus intermedius
Rectus femoris
Gluteus maximus
Tensor fasciae lata
Femoral
Femoral
Femoral
Femoral
Inferior gluteal
Superior gluteal
Lateral rotation of leg = medial rotation of thigh in knee flexionBiceps femoris, long head
Biceps femoris, short head
Gluteus maximus
Tensor fasciae lata
Tibial
Common peroneal
Inferior gluteal
Superior gluteal
Medial rotation of leg with knee flexedPopliteusTibial
Medial rotation of leg with knee extendedSemimembranosus
Semitendinosus
Gracilis
Sartorius
Sciatic (tibial)
Sciatic (tibial)
Obturator
Femoral
Ankle plantarflexionGastrocnemius
Soleus
Plantaris
Tibialis posterior
Flexor hallucis longus
Flexor digitorum longus
Peroneus longus
Peroneus brevis
Tibial
Tibial
Tibial
Tibial
Tibial
Tibial
Superficial peroneal
Superficial peroneal
Ankle dorsiflexionTibialis anterior
Extensor hallucis longus
Extensor digitorum longus
Peroneus tertius
Deep peroneal
Deep peroneal
Deep peroneal
Deep peroneal
Subtalar and midtarsal inversionTibialis anterior
Extensor hallucis longus
Tibialis posterior
Deep peroneal
Deep peroneal
Tibial
Subtalar and midtarsal eversionPeroneus longus
Peroneus brevis
Extensor digitorum longus
Peroneus tertius
Superficial peroneal
Superficial peroneal
Deep peroneal
Deep peroneal
1 Toe plantarflexion (MTPJ; IPJ)Flexor hallucis longus
Flexor hallucis brevis
Tibial
Medial plantar
2-5 Toes plantarflexion (MTPJs; IPJs)Flexor digitorum longus
Flexor accessorius (quadratus plantae)
Flexor digitorum brevis
Lumbricals
Interossei
Tibial
Lateral plantar
Medial plantar
Medial plantar, toe 2; lateral plantar toes 3-5
Lateral plantar
1 Toe dorsiflexionExtensor hallucis longus
Extensor hallucis brevis
Deep peroneal
Deep peroneal
2-5 Toes dorsiflexion
2-4 Toes dorsiflexion
Extensor digitorum longus
Extensor digitorum brevis
Deep peroneal
Deep peroneal
Toe abduction (away from midline of foot = adduction toward midline of body)
Toe 1
Toes 2-4
Toe 5
Abductor hallucis
Dorsal interossei
Abductor digit minimi
Medial plantar
Lateral plantar
Lateral plantar
Toe adduction (toward the midline of foot = abduction away from midline of body)
Toe 1
Toes 2-5
Adductor hallucis*
Plantar interossei
Lateral plantar
Lateral plantar

Note: Primary action of muscles is printed in normal type; muscles that give some contribution to this action are printed in italics .

The nerve supply to the lower limb (lower leg and foot) is derived from the sciatic and femoral nerves. Dysfunction or compromise of either of these nerves causes marked motor, sensory and autonomic effects in the lower leg and foot.

MTPJ, metatarsophalangeal joint; IPJ, interphalangeal joint.

muscle

A contractile organ of the body which produces movements of the various parts or organs. Typically it is a mass of fleshy tissue, attached at each extremity by means of a tendon to a bone or other structure. Muscles are classified according to structure as non-striated (or unstriated or unstriped or smooth) or striated (or striped), by control as voluntary or involuntary, or by location as cardiac, skeletal or visceral.
abducens muscle See lateral rectus muscle.
adducens muscle See medial rectus muscle.
agonistic muscle A muscle that performs the desired movement, or does the opposite to an antagonistic muscle. Example: the left lateral rectus is the agonistic muscle when the left eye turns to the left. See antagonistic muscle.
antagonistic muscle A muscle that opposes the action of another. Example: the right superior rectus muscle is the contralateral antagonist of the left superior oblique. See agonistic muscle; synergistic muscles.
Brücke's muscle See ciliary muscle.
ciliary muscle The smooth (unstriated and involuntary) muscle of the ciliary body. In a meridional section of the eye it has the form of a right-angled triangle, the right angle being internal and facing the ciliary processes. The posterior angle is acute and points to the choroid, the hypotenuse runs parallel with the sclera. Some of its fibres have their origin in the scleral spur at the angle of the anterior chamber, while other fibres take origin in the trabecular meshwork. The fibres radiate backward in three directions: (1) Fibres coursing meridionally or longitudinally more or less parallel to the sclera and can be traced posteriorly into the suprachoroid to the equator or even beyond. They end usually in branched stellate figures known as muscle stars with three or more rays to each. These fibres represent Brücke's muscle. (2) Other fibres course radially. These fibres lie deep in the longitudinal fibres from which they are distinguished by the reticular character of their stroma but are often very difficult to separate from the circular fibres. (3) The circular fibres (Müller's muscle) occupy the anterior and inner portion of the ciliary body and run parallel to the limbus. As a whole, these fibres form a ring.Innervation to the ciliary muscle (mainly parasympathetic fibres derived from the oculomotor nerve) is provided through the short ciliary nerves and stimulation causes a contraction of the muscle. However, a small amount of sympathetic supply is also believed to act and relax the muscle. Blood supply to the ciliary muscle is provided by the anterior and long posterior ciliary arteries. Contraction of the ciliary muscle causes a reduction in its length thus causing the whole muscle to move forward and inward. Consequently the zonule of Zinn, which suspends the lens, relaxes. This leads to a decrease in the tension in the capsule of the lens allowing it to become more convex and thereby providing accommodation. Syn. Bowman's muscle. See mechanism of accommodation; adrenergic receptors; ciliary body; scleral spur; Helmholtz's of accommodation theory; zonule of Zinn.
muscle cone A structure formed by the sheath of the four recti muscles as they pass forward from their common origin at the apex of the orbit in the fibrous ring called the annulus of Zinn (and around the optic nerve) to be inserted into the sclera around the eyeball. Some authors consider the muscle cone to include the superior oblique muscle. See annulus of Zinn.
dilator pupillae muscle Smooth (unstriated and involuntary) muscle whose fibres constitute the posterior membrane of the iris. This muscle extends from the ciliary body close to the margin of the iris where it fuses with the sphincter pupillae muscle. Contraction of the dilator pupillae muscle draws the pupillary margin towards the ciliary body and therefore dilates the pupil. This muscle is supplied by the sympathetic fibres in the long ciliary nerves and by a few parasympathetic fibres. See adrenergic receptors; sphincter pupillae muscle; mydriatic.
elevator muscle's See inferior oblique muscle; superior rectus muscle.
external rectus muscle See lateral rectus muscle.
extraocular muscle's The striated (voluntary) muscles that control the movements of the eyes. There are six such muscles: four recti muscles (lateral rectus, medial rectus, superior rectus and inferior rectus) which move the eye more or less around the transverse and vertical axes, and two oblique muscles (inferior oblique and superior oblique) which move the eyes obliquely. The muscles are composed of striated fibres of varying length, mostly running parallel to the direction of the muscle and united by fibrous connective tissue. They have a greater ratio of nerve fibres to muscle fibres than other striated muscles of the body. The fibre thickness varies from 3 to 50 μm, although functionally there seem to be two main types of fibres, the fast and the slow fibres. The former are the thickest and probably responsible for the fast movements of the eyes (saccades) and the latter consist of thin fibres. The tendons (bands of connective tissue) at one end of each extraocular muscle are attached to bones. This is the origin of the muscle. At the other end of the muscle the tendon is attached to the eye and this area is called the insertion. The substance proper of the muscle is called the belly. Contraction of a muscle occurs in the direction of its constituent fibres and causes a shortening of the muscle. Consequently the eye turns in a given direction depending upon which extraocular muscle is contracting. Contraction results from nervous impulses arriving at the motor end-plate (the junction between an axon and a striated muscle fibre) of the muscle through one of the ocular motor nerves. This causes a neurotransmitter substance to be discharged in the microscopic gap between the end-plate and a muscle fibre. These muscles also possess specialized receptors called muscle spindles, which are small groups of muscle fibres that are provided with both a sensory and a motor nerve supply. There are between 12 and 50 in each muscle. The muscle spindles provide a constant and continuous monitoring of the degree of tension of the muscle itself. Syn. extrinsic muscles; oculorotary muscles. See cholinergic; felderstruktur fibres; motor unit; strabismus surgery; motility test; three-step test.
extrinsic muscle's See extraocular muscles.
eyelid retractor muscle's See levator palpebrae superioris muscle; Müller's palpebral muscles.
Horner's muscle A thin layer of fibres that originates behind the lacrimal sac from the upper part of the posterior lacrimal crest (a ridge on the lacrimal bone which borders the fossa for the lacrimal sac). The muscle passes outward and forward and divides into two slips surrounding the canaliculi. It then becomes continuous with the pretarsal portions of the orbicularis muscle of the upper and lower lids and with the muscle of Riolan. Horner's muscle may be involved in tear drainage through action on the lacrimal sac. Syn. pars lacrimalis muscle; tensor tarsi muscle. See muscle of Riolan.
inferior oblique muscle (IO) One of the extraocular muscles, it takes its origin at the antero-medial corner of the floor of the orbit. It passes underneath the inferior rectus in a backward direction (making an angle of about 50º with the sagittal plane of the eye), then under the lateral rectus to be inserted by the shortest tendon of all extraocular muscles on the posterior, temporal portion of the eyeball, for the most part below the horizontal meridian, some 5 mm away from the optic nerve. It is innervated by the oculomotor nerve and it extorts (main action), elevates and abducts the eyeball when the eye is in the primary position. Combined with the action of the superior rectus muscle, it directs the eye upward (Fig. M15). See Bielschowsky's head tilt test; three-step test.
inferior rectus muscle (IR) This is the shortest of the four recti muscles. It arises from the lower part of the annulus of Zinn, runs forward, downward and outward (making an angle of about 23º with the sagittal plane) and inserts into the inferior portion of the sclera about 6.5 mm from the corneal limbus. It is innervated by the inferior division of the oculomotor nerve and it depresses (main action), adducts and extorts the eyeball when the eye is in the primary position (Fig. M15). See annulus of Zinn; Müller's palpebral muscles; Bielschowsky's head tilt test.
inferior tarsal muscle See Müller's palpebral muscles.
internal rectus muscle See medial rectus muscle.
intraocular muscle's The smooth (unstriated and involuntary) muscles found within the eye. They are the ciliary, the dilator pupillae and the sphincter pupillae muscles. Syn. intrinsic muscles. See cholinergic.
lateral rectus muscle (LR) One of the extraocular muscles, it arises from both the lower and upper parts of the annulus of Zinn which bridge the superior orbital fissure. The muscle passes forward along the lateral wall of the orbit, crosses the tendon of the inferior oblique muscle and inserts into the sclera about 6.9 mm from the corneal limbus. It is innervated by the abducens nerve and it abducts the eyeball when the eye is in the primary position (Fig. M15). Syn. external rectus muscle; abducens muscle. See annulus of Zinn; check ligament.
levator palpebrae superioris muscle Striated muscle that arises from the under surface of the lesser wing of the sphenoid bone above and in front of the optic canal. It passes forward below the roof of the orbit and above the superior rectus muscle and terminates in a tendinous expansion or aponeurosis (also called levator aponeurosis), which spreads out in a fan-shaped manner so as to occupy the whole breadth of the orbit and thus gives the whole muscle the form of an isosceles triangle. From the inferior surface of the aponeurosis arises a thin sheet of smooth muscle fibres called Müller's palpebral muscle (or superior tarsal muscle) which inserts into the posterior margin of the superior tarsal plate and into the superior fornix of the conjunctiva. These smooth muscle fibres are innervated by sympathetic nerves from the superior cervical sympathetic ganglion and assist in elevating the upper eyelid. The fibres of the aponeurosis are attached to the anterior margin of the superior tarsal plate while some fuse with bundles of the orbicularis oculi muscle to attach to the skin. These latter sets of fibres produce the horizontal skin crease of the upper eyelid. The striated levator aponeurosis is innervated by the superior division of the oculomotor nerve and elevates the upper eyelid. Its antagonist is the orbicularis muscle. See orbicularis muscle.
medial rectus muscle (MR) One of the extraocular muscles, it arises from the medial part of the annulus of Zinn. It passes forward along the medial wall of the orbit and is inserted into the sclera about 5.5 mm from the corneal limbus. It is innervated by the inferior division of the oculomotor nerve and it adducts the eyeball when the eye is in the primary position (Fig. M15). Syn. internal rectus muscle; adducens muscle. See annulus of Zinn; check ligament.
Müller's muscle See ciliary muscle.
Müller's palpebral muscle's Smooth muscles of the eyelids. The superior one (also called superior tarsal muscle) originates from the under surface of the levator palpebrae superioris muscle and passes below to insert into the upper margin of the tarsal plate of the upper eyelid. The inferior one (also called inferior tarsal muscle) originates from the muscular fascia covering the inferior rectus muscle. It extends upward and inserts into the bulbar conjunctiva and the lower margin of the tarsal plate of the lower eyelid. Müller's palpebral muscles are innervated by sympathetic fibres and help in lifting the upper eyelid and depressing the lower eyelid. They are sometimes referred to as the eyelid retractors.
oculorotary muscle's See extraocular muscles.
orbicularis muscle A thin oval sheet of striated muscle that surrounds the palpebral fissure, covers the eyelids and spreads out for some distance onto the temple, forehead and cheek. It consists of three portions: (1) The marginal or ciliary portion (muscle of Riolan). (2) The palpebral portion (also called the pars palpebralis muscle) which is the essential part of the muscle and is confined to the lids and may itself be divided into pretarsal portion whose fibres lie in front of the tarsal plates, and the preseptal portion whose fibres extend from the tarsal plates to the orbital margin. The palpebral portion is used in closing the eye without effort or in reflex blinking. (3) The orbital portion (also called the pars orbitalis muscle) which is found in the eyebrow, the temple, the forehead and the cheek. This portion of the muscle is used to close the eye tightly and the skin of the forehead, temple and cheek is drawn towards the inner side of the orbit. The orbicularis muscle is innervated by the facial nerve. Syn. sphincter oculi muscle. See ectropion; Horner's muscle; levator palpebrae superiotis muscle; muscle of Riolan; myokymia.
pars ciliaris muscle See muscle of Riolan.
pars lacrimalis muscle See Horner's muscle.
pars orbitalis muscle See orbicularis muscle.
pars palpebralis muscle See orbicularis muscle.
pupillary muscle's The dilator pupillae and the sphincter pupillae muscles.
muscle of Riolan The ciliary portion of the orbic-ularis muscle, it consists of very fine striated muscle fibres which lie in the dense tissue of the eyelids near their margin. It is continuous with Horner's muscle and encircles the eyelid margins mainly between the tarsal glands and the eyelash follicles. Its action is to bring the eyelid margins together when the eyes are closed. Syn. pars ciliaris muscle. See Horner's muscle; orbicularis muscle.
sphincter oculi muscle See orbicularis muscle.
sphincter pupillae muscle Smooth, circular muscle about 1 mm broad, forming a ring all round the pupillary margin near the posterior surface of the iris. It is innervated by parasympathetic fibres of the oculomotor nerve that synapse in the ciliary ganglion and by a few sympathetic fibres. Its contraction produces a reduction in the diameter of the pupil. See miotics; dilator pupillae muscle; pupil light reflex.
muscle spindle See extraocular muscles.
superior oblique muscle (SO) This is the longest and thinnest of the extraocular muscles. It arises above and medial to the optic foramen on the small wing of the sphenoid bone. It passes forward between the roof and medial wall of the orbit to the trochlea (which is in the form of a pulley made of fibrocartilage) located at the front of the orbit where it loops over and turns sharply backward, downward and outward (making an angle of about 55º with the sagittal plane), passes under the superior rectus and inserts into the sclera just behind the equator on the superior temporal portion of the eyeball. It is innervated by the trochlear nerve and it intorts (main action), depresses, and also abducts the eyeball when the eye is in the primary position (Fig. M15). See trochlear fossa; Bielschowsky's head tilt test; three-step test.
superior rectus muscle (SR) One of the extraocular muscles, it arises from the upper part of the annulus of Zinn. It passes forward and outward (making an angle of about 23º with the sagittal plane) and inserts into the sclera about 7.7 mm from the corneal limbus. It is innervated by the superior division of the oculomotor nerve and elevates (main action), adducts, and also intorts the eyeball when the eye is in the primary position (Fig. M15). See annulus of Zinn; Bielschowsky's head tilt test.
synergistic muscle's Muscles having a similar and mutually helpful action as, for example, the inferior rectus and superior oblique muscles in depressing the eyeball. See Table M5.
superior tarsal muscle See Müller's palpebral muscles.
tarsal muscle's See Müller's palpebral muscles.
tensor tarsi muscle See Horner's muscle.
yoke muscle's Muscles of the two eyes which simultaneously contract to turn the eyes in a given direction. Example: the medial rectus of the right eye and the lateral rectus of the left eye when turning the eyes to the left. See Hering's law of equal innervation; motility test; version.
Fig. M15 Extraocular muscles of the eye (the left superior rectus muscle is not shown to allow a clearer view of the muscles underneath)enlarge picture
Fig. M15 Extraocular muscles of the eye (the left superior rectus muscle is not shown to allow a clearer view of the muscles underneath)

Table M5 Agonistic, antagonistic and synergistic extraocular muscles
agonistipsilateral antagonistipsilateral synergist(s)contralateral synergist
lateral rectusmedial rectussuperior obliquemedial rectus
inferior oblique
medial rectuslateral rectussuperior rectuslateral rectus
inferior rectus
superior rectusinferior rectusinferior obliqueinferior oblique
inferior rectussuperior rectussuperior obliquesuperior oblique
superior obliqueinferior obliquesuperior rectusinferior rectus
inferior obliquesuperior obliqueinferior rectussuperior rectus

Table M6 Innervation and action of the six extraocular muscles
muscleinnervationaction in the primary position
medial rectusoculomotor (III)adduction
lateral rectusabducens (VI)abduction
inferior rectusoculomotor (III)depression*
adduction
extorsion
superior rectusoculomotor (III)elevation
adduction
intorsion
inferior obliqueoculomotor (III)extorsion
elevation
abduction
superior obliquetrochlear (IV)intorsion
depression
abduction
*Bold characters indicate main action.

Table M7 Intraocular muscles of the eyeball (unstriated muscles)
name of musclenerve supplyaction
sphincter pupillaeparasympathetic via oculomotor nerveconstricts pupil
dilator pupillaesympathetic via trigeminal nervedilates pupil
ciliaryparasympathetic via oculomotor nervecontrols shape of lens in accommodation

Table M8 Yoke muscles
right eyeleft eyeversion*
lateral rectusmedial rectusto the right
medial rectuslateral rectusto the left
superior rectusinferior obliqueup and to the right
inferior rectussuperior obliquedown and to the right
superior obliqueinferior rectusdown and to the left
inferior obliquesuperior rectusup and to the left
*The directions refer to those of the patient.

Table M9 Dimensions of the four recti muscles
muscle length (mm)insertion distance from limbus (mm)tendon length (mm)
lateral rectus486.98.8
medial rectus405.53.7
inferior rectus406.55.5
superior rectus427.75.8

mus·cle

(mŭs'ĕl) [TA]
Primary tissue, consisting predominantly of highly specialized contractile cells, which may be classified as skeletal muscle, cardiac muscle, or smooth muscle.
Synonym(s): musculus [TA] .
[L. musculus]

muscle(s),

n an organ that, by cellular contraction, produces the movements of life. The two varieties of muscle structure are striated, which includes all the muscles in which contraction is voluntary and the heart muscle (in which contraction is involuntary), and unstriated, smooth, or organic, which includes all the involuntary muscles (except the heart), such as the muscular layer of the intestines, bladder, and blood vessels. See also each of the individual muscles of the head and neck as they are listed.
muscle, buccinator
(buk´sinātər),
n the muscle consisting of three bands and composing the wall of the cheek between the mandible and the maxilla; it causes the cheek to stay tight to the teeth and the lip corners to pull inward. It is often known as the “cheek muscle.”
muscle, ciliary
(sil´ēer´ē),
n a tiny smooth muscle at the junction of the cornea and sclera, consisting of two groups of fibers: circular fibers, which exert parasympathetic control through the oculomotor nerve and the ciliary ganglion, and radial fibers, which exert sympathetic control. Ciliary muscles are responsible for accommodation for far vision through flattening of the lens.
muscle, concentric, contraction,
n See contraction, muscle, concentric.
muscle contraction,
n See contraction, muscle.
muscle, digastric
n suprahyoid muscle that helps activate the jaw for mastication and swallowing. It has both an anterior and a posterior belly. See also deglutition; mastication; muscle, hyoid.
muscle, eccentric, contraction,
n See contraction, muscle, eccentric.
muscle, elasticity of, physical,
n the physical quality of being elastic, of yielding to passive physical stretch.
muscle, elasticity of, physiologic,
n the biologic quality, unique for muscle, of being able to change and resume size under neuromuscular control.
muscle fatigue,
n the depletion of the metabolites necessary to sustain or repeat a muscle contraction.
muscle fiber,
n the cell of muscle tissue. The three types of muscle fibers are striated (voluntary), cardiac, and smooth (involuntary).
muscle, functional changes of,
n.pl asymmetric modifications in length, diameter, and bulk of muscle fibers as a result of variations in function. Muscle responds to normal function by maintenance of bulk. An increase in bulk is caused by an increase in the number of capillaries and in the mean diameter of individual muscle fibers. The response to function accounts for the asymmetry of the musculature, which is frequently found when the growth patterns have been influenced by a traumatogenic agent such as disease, injury, or surgery, and also by the functional processes of the body itself, such as posture and habit. Asymmetry is not necessarily pathologic; i.e., it may be the result of differences in habits of chewing, incision, speech sounds, and facial gestures.
muscle, genioglossus
(jē´nēōglôs´us),
n an extrinsic tongue muscle that originates from the genial tubercles of the mandible and extends inside the tongue. It aids in tongue extension and prevents respiratory obstruction.
muscle, geniohyoid
(jē´nēōhī´oid),
n suprahyoid muscle attached to the superior surface of the hyoid bone. This muscle, which is used for mastication and swallowing, originates on the genial tubercles of the mandible and extends along the floor of the oral cavity. See also deglutition; mastication; muscle, hyoid.
muscle, hyoglossus
(hī´ōglôs´əs),
n an extrinsic tongue muscle that originates from the hyoid bone and extends on the lateral surface of the body of the tongue. It depresses the tongue during mastication and speech.
muscle, hypertenseness,
n an increased muscular tension that is not easily released but that does not prevent normal lengthening of the muscle. Hypertenseness is found in patients with general nervousness.
muscle, innervation of, reciprocal,
n a phenomenon of antagonistic muscles demonstrated during a concentric contraction such as that of the temporal muscle. Innervation of the antagonist, the external pterygoid muscle, is partially inhibited, so that freedom of action in flexing the temporomandibular joint is possible. This phenomenon demonstrates inhibition of antagonistic skeletal muscles in a reflex arc brought about automatically by a reduction of the motor discharges from the central nervous system. One of the two muscles in the reflex arc is activated, and the activity of the other is depressed.
muscle, isometric, contraction,
n See contraction, muscle, isometric.
muscle, isotonic, contraction,
n See contraction, muscle, isotonic.
muscle, lateral pterygoid
(lat´ərəl ter´igoid),
n the muscle whose superior head attaches to the sphenoid bone and whose inferior head attaches to the pterygoid plate. This muscle moves the jaw from side to side. Also known as the
external pterygoid muscle.
muscle, masseter
(məsē´tər),
n one of the four muscles of mastication. The thick rectangular muscle in the cheek that functions to close the jaw. The masseter muscle arises from the zygomatic arch and inserts into the mandible at the corner of the jaw.
Enlarge picture
Palpation of the masseter muscle.
muscle memory,
n a kinesthetic phenomenon by which a muscle or set of muscles may involuntarily produce movement that follows a pattern that has become established by frequent repetition over a long period.
muscle, mentalis
(mental´əs),
n the muscle in the chin that originates in the incisive fossa and is inserted into the skin of the chin; it lifts the lower lip and wrinkles the skin of chin.
muscle, mylohyoid,
n suprahyoid muscle originating from the mandible. It helps to raise the tongue and lower the mandible for mastication and swallowing and also forms the floor of the oral cavity. See also deglutition; mastication; muscles, hyoid.
muscle, omohyoid
n infrahyoid muscle with both inferior and superior bellies. It is used for chewing and swallowing. See also muscles, hyoid.
muscle, orbicularis oris
(orbik´yəlar´əs or´is),
n the muscle that encircles the oral cavity; it encompasses both fibers proper to the lips as well as the adjacent facial muscles. Also known as the “kissing muscle” for its puckering role, it is intimately involved in the opening and closing of the oral cavity.
muscle, palatoglossal
(pal´ətōglos´əl),
n the interior palate muscle that serves to raise and lower the posterior part of the tongue.
muscle, palatopharyngeus
(pal´ətōferin´jēəs),
n the muscle that extends from the soft palate to the walls of the laryngopharynx and the thyroid cartilage to form the posterior facial pillars; it is used during swallowing to cover the opening of the nasopharynx by moving the palate and the posterior pharyngeal wall.
muscle, physical characteristics of primary, elasticity,
n.pl a muscle is an elastic body. Its individual fibers follow Hooke's law of elastic bodies: that is, the amount of elongation is proportional to the stretching force. The muscle organs contain tissue other than muscle fibers and thus deviate slightly from this law. The human muscle fiber can contract to about half its total length.
muscle, platysma
(plətiz´mə),
n the muscle that extends from the clavicle and shoulder, along the neck, to the mandible and the muscles surrounding the oral cavity; it allows the corners of the oral cavity to be pulled down in a grimace and the skin of the neck to be raised into ridges and depressions.
muscle, regeneration of reproduction or repair of muscle fiber,
n a sequela to many types of muscle damage. Reparation is always associated with the proliferation of sarcolemmic nuclei. Connective tissue elements do not participate in this process except to bridge the gap and offer support for the regenerative fibers. The regenerative process takes place in two forms: regeneration by budding from the surviving parts of the muscle fibers, which occurs when segments of the muscle fiber and its sheath are destroyed, and regeneration by proliferation of cellular bands, which occurs when the sarcolemmic nuclei are spared and can form a sarcoplasmic band by linkage of the cytoplasmic processes.
muscle relaxation,
n the resting state of a muscle fiber or a group of muscle fibers.
muscle reposition,
n surgical replacement of a muscle attachment into a more acceptable functional position.
muscle, sequence of, development,
n the pattern of embryologic muscular development. The muscles of the neck and trunk are the first to develop; they are followed by the lingual and facial musculature and then by the distal and proximal appendicular musculature.
muscle, smooth,
n the simplest of the three types of muscle (smooth, striated, and cardiac). It is the muscle of the lining of the digestive tract, ducts of glands, and viscera associated with the gut. It also supplies the muscles for the genitourinary tract, structures of the blood vessels, connective tissues of the mucous membranes, and skin with its appendages. A typical fiber is a slender, spindle-shaped body averaging a few tenths of a millimeter in length. There is a single, centrally striated nucleus. The cytoplasm appears homogeneous. The cells are arranged in bands, or bundles, with interspersed connective tissue fibers uniting them into an effective common mass. They are innervated in part by nerve fibers and in part by the contraction of adjacent muscle tissues. The digestive tract, particularly, demonstrates waves of contraction that pass along a band of smooth muscle.
muscle, spasticity of,
n increased muscular tension of antagonists that prevents normal movement; caused by an inability to relax (a loss of reciprocal inhibition) resulting from a lesion of the upper motor neuron.
muscle, sternocleidomastoid (SCM),
n a muscle of the neck that is attached to the mastoid process and superior nuchal line and by separate heads to the sternum and clavicle. It functions with other muscles to turn the head from side to side and tilt the head to one side or the other. It separates the neck region into triangles.
muscle, sternothyroid
(stur´nōthī´roid),
n infrahyoid mus-cle that runs from the sternum to the thyroid cartilage and depresses the larynx and the thyroid cartilage for mastication and swallowing. See also deglutition; mastication; muscle, hyoid.
muscle, striated
n skeletal muscles forming the bulk of the body; the voluntary muscles derived from the myotomes of the embryo. Generally, they are organized as formed muscles that attach to and move the skeletal structures. The cells are large, elongated, and cylindric, with lengths ranging from 1 mm to several centimeters. The cells have multiple nuclei that are peripherally situated and scattered along the length of the fiber. The fiber contains a large number of elongated fibers that, under the microscope, appear as the alternating light and dark bands that give the characteristic striated appearance of striated muscle. The dimensional relationships between these light and dark bands are altered during contraction of the muscle fiber. The potential interaction between these bands permits the wide range of selective purposeful and rapid activity of the skeletal muscles.

muscle

an organ composed of bundles of fibers that has the power to contract and hence to produce movement. Muscles are responsible for locomotion and help support the body, generate heat and perform a number of other functions. They are of two varieties: striated (or striped, voluntary or skeletal), which makes up most of the meat of a carcass, and smooth (unstriated), which includes all the involuntary muscle of the viscera, heart and blood vessels.
Skeletal muscle fibers range in length from a few millimeters to many centimeters. They also vary in color from white to deep red. Each muscle fiber receives its own nerve impulses, which trigger fine and varied motions. At the signal of an impulse traveling down the nerve, the muscle fiber changes chemical energy into mechanical energy, and the result is muscle contraction. At least two major types of muscle fiber have been identified by histochemical techniques: type I (red) fibers, which have a slow contraction; and type II (white) fibers, which have a fast contraction.
Some muscles are attached to bones by tendons. Others are attached to other muscles, and to skin, producing, for example, the skin twitch, the eye blink and hair erection. Parts of the walls of hollow internal organs, such as the heart, stomach and intestines and also blood vessels, are composed of muscles. See also muscular. For a complete list of named muscles see Table 13.

agonistic muscle
prime mover; a muscle opposed in action by another muscle, called the antagonist.
antagonistic muscle
one that counteracts the action of another muscle (the agonist).
appendicular muscle
one of the muscles of a limb.
arrector pili muscle
small, smooth muscle attached to the bulb of the hair which causes erection of the hair and compression of the attending sebaceous gland when it contracts.
arterial muscle
part of the tunica media; smooth muscle fibers arranged in a circular pattern around the lumen.
articular muscle
one that has one end attached to the capsule of a joint.
axial muscle
1. muscles derived from the somites in the embryo.
2. the muscles around the vertebral column.
muscle biopsy
sample of living muscle obtained by excision or punch.
cardiac muscle
striated involuntary muscle with branched fibers and containing modified fibers which act as cardiac conducting cells.
congenital muscle defects
may be environmental, e.g. nutritional muscular dystrophy, or inherited, e.g. splayleg of piglets.
congenital type II muscle fiber hypertrophy
occurs in the hip joint musculature in German shepherd dogs but there is no detectable abnormality of gait.
cutaneous muscle
striated muscle that inserts into the skin.
double muscle
see myofiber hyperplasia.
esophageal muscle
the tunica muscularis of the esophagus in most domestic animals is mostly striated; in pigs, horses and cats there are small segments of smooth muscle; in birds the entire tunic is smooth muscle.
extraocular m's
the six or seven voluntary muscles that move the eyeball: dorsal, ventral, medial and lateral recti, dorsal and ventral oblique, and retractor bulbi muscles.
extrinsic muscle
one that originates in another part than that of its insertion, e.g. those originating outside the eye, which move the eyeball.
fast-twitch skeletal muscle
two of the three types of skeletal muscle are pale in color and fast-twitch—type IIa (fast-twitch oxidative-glycolytic), type IIb (fast-twitch glycolytic). Type IIa fibers are fatigue-resistant, type IIb fatigue easily.
muscle fiber
see muscle (above).
fixation m's, fixator m's
accessory muscles that serve to steady a part.
hamstring m's
the biceps, semimembranosus and semitendinosus muscles. See also hamstring.
intraocular m's
the intrinsic muscles of the eyeball.
intrinsic muscle
one whose origin and insertion are both in the same part or organ, such as those entirely within the eye.
involuntary muscle
see smooth muscle (below).
iridial muscle
layers of circular (sphincter) and radial (dilator) muscles. See also iris.
jaw muscle
see Table 13.1H muscles of mastication.
laryngeal muscle
see Table 13.1E muscles of the larynx.
limb muscle
see Table 13.3, 13.4 muscles of the fore- and hindlimbs.
masseter muscle
the principal muscle of mastication. See also Table 13.1H.
mylohyoid muscle
see Table 13.1D muscles of the hyoid apparatus.
muscle neoplasms
of striated muscle—rhabdomyoma, rhabdomyosarcoma; of plain muscle—leiomyoma, leiomyosarcoma.
muscle nonstriated
see smooth muscle (below).
orbicular muscle
one that encircles a body opening, e.g. the eye or mouth.
muscle-paralyzing drugs
drugs which produce neuromuscular blockade, used as muscle relaxants during surgical procedures. Include d-tubocurarine, alcuronium chloride, pancuronium, vecuronium, atracurium besylate, succinylcholine.
red muscle
type 1 fibers predominate with slow contraction cycles and aerobic metabolism.
muscle rupture
the muscle may have torn away from its insertion, in which case the tendon will be slack, or it may be a complete or partial separation of the belly of the muscle, when the muscle will be swollen and hard. Structural and conformational changes may result, e.g. in rupture of the gastrocnemius muscle, and the hernias caused by rupture of the ventral abdominal muscles or the diaphragm.
skeletal m's
striated muscles that are attached to bones and typically cross at least one joint. Called also voluntary or striated muscles.
slow-twitch skeletal muscle
type 1 skeletal muscle fibers are bright red and contain large amounts of myoglobin; not easily fatigued.
smooth muscle
plain or involuntary muscle which powers the internal organs and is controlled by the autonomic nervous system; slow contracting cycles and fatigue resistant. Two types listed, visceral and vascular.
sphincter muscle
a ringlike muscle that closes a natural orifice; called also sphincter.
muscle spindle
sensory end-organ attached to the perimysial connective tissue of the muscle.
muscle strain
soreness and stiffness in a muscle due to overexertion or contusion, especially in muscles that have not been conditioned for hard use; some of the muscle fibers may actually tear.
striated muscle
see skeletal muscles (above).
synergic m's
those that assist one another in action.
temporal muscle
a significant muscle of mastication. See also Table 13.1H.
muscle-tendon junction
the union between connective tissue investing muscles and anchoring connective tissue.
type I muscle fiber
see slow-twitch skeletal muscle (above).
type II muscle fiber
see fast-twitch skeletal muscle (above).
type II muscle fiber deficiency
a relative deficiency of type II muscle fibers, with a predominance of type I fibers. An inherited defect in Labrador retrievers. Clinical signs include stunted growth, and muscle weakness and abnormal gait, which subside with rest, from an early age.
voluntary muscle
see skeletal muscle (above).
white muscle
consist of type II fibers; fast contraction fibers and aerobic metabolism are characteristic.
yoked m's
those that normally act simultaneously and equally, as in moving the eyes.

Patient discussion about muscle

Q. What are muscle cramps caused from? I am a 30 year old woman and am pregnant. I keep on getting a muscle cramps on the back on my lower leg. It really hurts! What is causing it and how can I prevent it?

A. You can get muscle cramps almost anywhere in your body during pregnancy, but the most common site is your calves. Although the spasms may only last a short time, they can be very severe.
No one knows for certain what causes leg cramps in pregnancy, though there are some theories: Deficiencies in salt, calcium, magnesium and vitamin C or changes in blood circulation.
To prevent it make sure to stretch your muscles before bed and if you do get a cramp, immediately stretch your calf muscles: Straighten your leg, heel first, and gently flex your toes back toward your shins. It might hurt at first, but it will ease the spasm and the pain will gradually go away.

Q. Why do my muscles sometimes burn when I'm exercising? I do exercise twice a day. Why do my muscles sometimes burn when I'm exercising?

A. The idea that lactic acid is what causes muscle burn during exercise is outdated and not supported by the most recent research. Lactic acid is actually a primary source of fuel during anaerobic exercise.

Muscle cells take up glucose (muscle glycogen) and convert them into lactic acid, which the mitrochondria in the cells then use for energy. The old theory was that lactic acid was a waste product that hindered performance. New scholarship on this actually shows that lactic acid is a SOURCE of fuel, not a "dead end as far as energy production is concerned."

Much of this new thinking has come from research performed by Dr. George Brooks at the University of California - Berkely. You can read more here: http://berkeley.edu/news/media/releases/2006/04/19_lactate.shtml

Researchers also now believe that muscle acidosis (that burning sensation during exercise)is not caused by increases in lactate within the muscle, but rather by a completely separate reaction when ATP is h

Q. What can I do to build muscle and develop immunity? I'm Mickey, 21. My height is 5’5” and I weigh 176 lbs. I love out door games especially soccer. I have poor immunity that I get sick very often. What can I do to build muscle and develop immunity?

A. You must keep your GI tract healthy. Eat plenty of soluble and insoluble fiber every day minimum of 25 grams, but gradually shoot up to 35 grams. Include yogurt or encapsulated probiotics in your daily diet. The more robust your GI tract, the more available nutrients such as glutamine is for anabolic muscle metabolism. Another nutrient is ImmunoLin, a purified source of immunoglobin G (IgG), which fights off viruses that may enter the body through the GI tract. Research has shown that IgG not only improves get immune health, which helps you to stay healthy, but also helps people who suffer from various allergies. Do exercise regularly. If you follow the above tips, I am sure you will get the desired results.

More discussions about muscle
References in classic literature ?
A strong man in a show that came to Thwaite once showed me how to exercise my arms an' legs an' every muscle in my body.
He practiced continually with the spear, throwing it at some object ahead hour by hour as they traveled their loitering way, until he gained a proficiency such as only youthful muscles may attain to speedily.
Instantly my brain cleared and there swept back across the threshold of my memory the vivid picture of the horrors of that ghostly Arizona cave; again, as on that far-gone night, my muscles refused to respond to my will and again, as though even here upon the banks of the placid Hudson, I could hear the awful moans and rustling of the fearsome thing which had lurked and threatened me from the dark recesses of the cave, I made the same mighty and superhuman effort to break the bonds of the strange anaesthesia which held me, and again came the sharp click as of the sudden parting of a taut wire, and I stood naked and free beside the staring, lifeless thing that had so recently pulsed with the warm, red life-blood of John Carter.
There are nerves and muscles in our frames whose functions and whose methods of working it seems a sort of sacrilege to describe by cold physiological names and surgical technicalities, and the monk's talk suggested to me something of this kind.
Now she was within ten feet of the two unsuspecting little playfellows--carefully she drew her hind feet well up beneath her body, the great muscles rolling under the beautiful skin.
Suddenly the broad muscles and lines of the count's face began to twitch.
Their powerful muscles lay just underneath their skins, like bunches of tough rope, and the weakest Growleywog was so strong that he could pick up an elephant and toss it seven miles away.
It was no member of the House of Lords who swung swiftly and grimly through the tangled forest or trod with untiring muscles the wide stretches of open plain--it was a great he ape filled with a single purpose that excluded all thoughts of fatigue or danger.
But steadfastly it kept on its way, strangely ignoring the cravings of appetite that at another time would have sent the rolling, fur-clad muscles flying at some soft throat.
Their protruding eyes simply stared and occasionally the muscles of their mouths opened and closed.
It is true that Number Thirteen knew nothing whatever of personal combat, but Number One had but little advantage of him in the matter of experience, while the former was equipped with great natural intelligence as well as steel muscles no whit less powerful than his deformed predecessor.
But the brain, and the agility, and the muscles that had coped with the mighty strength and cruel craftiness of Terkoz and Numa in the fastness of their savage jungle were not to be so easily subdued as these apaches of Paris had believed.