muscle fiber (redirected from Atrial myocytes)

fiber /fi·ber/ (fi´ber)

1. an elongated, threadlike structure.

2. nerve f.

3. dietary f.

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A fibers  myelinated afferent or efferent fibers of the somatic nervous system having a diameter of 1 to 22 μm and a conduction velocity of 5 to 120 meters per second; they include the alpha, beta, delta, and gamma fibers.

accelerating fibers , accelerator fibers adrenergic fibers that transmit the impulses which accelerate the heart beat.

adrenergic fibers  nerve fibers, usually sympathetic, that liberate epinephrine or related substances as neurotransmitters.

afferent fibers , afferent nerve fibers nerve fibers that convey sensory impulses from the periphery to the central nervous system.

alpha fibers  motor and proprioceptive fibers of the A type, having conduction velocities of 70 to 120 meters per second and ranging from 13 to 22 μm in diameter.

alveolar fibers  fibers of the periodontal ligament extending from the cementum of the tooth root to the walls of the alveolus.

arcuate fibers  the bow-shaped fibers in the brain, such as those connecting adjacent gyri in the cerebral cortex, or the external or internal arcuate fibers of the medulla oblongata.

association fiber  one of the nerve fibers connecting different cortical areas within one hemisphere.

autonomic nerve fibers  nerve fibers that innervate smooth muscle and glandular tissues, either stimulating and activating the muscle or tissue (autonomic efferent f's) or receiving sensory impulses from them (autonomic afferent f's) .

B fibers  myelinated preganglionic autonomic axons having a fiber diameter of ≤ 3 μm and a conduction velocity of 3 to 15 meters per second; these include only efferent fibers.

basilar fibers  those that form the middle layer of the zona arcuata and the zona pectinata of the organ of Corti.

beta fibers  motor and proprioceptive fibers of the A type, having conduction velocities of 30 to 70 meters per second and ranging from 8 to 13 μm in diameter.

C fibers  unmyelinated postganglionic fibers of the autonomic nervous system, also the unmyelinated fibers at the dorsal roots and at free nerve endings, having a conduction velocity of 0.6 to 2.3 meters per second and a diameter of 0.3 to 1.3 μm.

collagen fibers , collagenous fibers the soft, flexible, white fibers which are the most characteristic constituent of all types of connective tissue, consisting of the protein collagen, and composed of bundles of fibrils that are in turn made up of smaller units (microfibrils), which show a characteristic crossbanding with a major periodicity of 65 nm.

commissural fiber  one of the nerve fibers which pass between the cortex of opposite hemispheres of the brain, or between two sides of the brain stem or spinal cord.

dietary fiber  that part of whole grains, vegetables, fruits, and nuts that resists digestion in the gastrointestinal tract; it consists of carbohydrate (cellulose, etc.) and lignin.

efferent fibers , efferent nerve fibers nerve fibers that convey motor impulses away from the central nervous system toward the periphery.

elastic fibers  yellowish fibers of elastic quality traversing the intercellular substance of connective tissue.

fusimotor fibers  efferent A fibers that innervate the intrafusal fibers of the muscle spindle.

gamma fibers  any A fibers that conduct at velocities of 15 to 40 meters per second and range from 3 to 7 μm in diameter, comprising the fusimotor fibers.

gray fibers  unmyelinated nerve fibers found largely in the sympathetic nerves.

insoluble fiber  that not soluble in water, composed mainly of lignin, cellulose, and hemicelluloses and primarily found in the bran layers of cereal grains.

intrafusal fibers  modified muscle fibers which, surrounded by fluid and enclosed in a connective tissue envelope, compose the muscle spindle.

Mahaim fibers  specialized tissue connecting components of the conduction system directly to the ventricular septum.

motor fibers  efferent fibers.

Müller's fibers  elongated neuroglial cells traversing all the layers of the retina, forming its principal supporting element.

muscle fiber  any of the cells of skeletal or cardiac muscle tissue. Skeletal muscle fibers are cylindrical multinucleate cells containing contracting myofibrils, across which run transverse striations. Cardiac muscle fibers have one or sometimes two nuclei, contain myofibrils, and are separated from one another by an intercalated disk; although striated, cardiac muscle fibers branch to form an interlacing network.

myelinated fibers  grayish white nerve fibers whose axons are encased in a myelin sheath, which may in turn be enclosed by a neurilemma.

nerve fiber  a slender process of a neuron, especially the prolonged axon which conducts nerve impulses away from the cell; classified as either afferent or efferent according to the direction the impulses flow, and either myelinated or unmyelinated according to whether there is or is not a myelin sheath.

osteogenetic fibers , osteogenic fibers precollagenous fibers formed by osteoclasts and becoming the fibrous component of bone matrix.

preganglionic fibers  the axons of preganglionic neurons.

pressor fibers  nerve fibers which, when stimulated reflexly, cause or increase vasomotor tone.

projection fiber , projection nerve fibers one of the nerve fibers that connect the cerebral cortex with the subcortical centers, the brain stem, and the spinal cord.

Purkinje fibers  modified cardiac muscle fibers composed of Purkinje cells, occurring as an interlaced network in the subendothelial tissue and constituting the terminal ramifications of the cardiac conducting system.

radicular fibers  fibers in the roots of the spinal nerves.

reticular fibers  immature connective tissue fibers staining with silver, forming the reticular framework of lymphoid and myeloid tissue, and occurring in interstitial tissue of glandular organs, the papillary layer of the dermis, and elsewhere.

sensory fibers  afferent fibers.

Sharpey's fibers 

1. collagenous fibers that pass from the periosteum and are embedded in the outer circumferential and interstitial lamellae of bone.

2. terminal portions of principal fibers that insert into the cementum of a tooth.

soluble fiber  that with an affinity for water, either dissolving or swelling to form a gel; it includes gums, pectins, mucilages, and some hemicelluloses, and is primarily found in fruits, vegetables, oats, barley, legumes, and seaweed.

somatic nerve fibers  nerve fibers that stimulate and activate skeletal muscle and somatic tissues (somatic efferent f's) or receive impulses from them (somatic afferent f's) .

spindle fibers  the microtubules radiating from the centrioles during mitosis and forming a spindle-shaped configuration.

traction fibers  spindle f's.

unmyelinated fibers  nerve fibers that lack the myelin sheath.

vasomotor fibers  unmyelinated nerve fibers going chiefly to arteriolar muscles.

visceral nerve fibers  autonomic nerve f's.

white fibers  collagenous f's.

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muscle fiber

n.

A cylindrical multinucleate cell composed of myofibrils that contract when stimulated.

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muscle fiber,

any of the cells of skeletal or cardiac muscle tissue. Skeletal muscle fibers are cylindrical polynuclear cells containing contracting myofibrils, across which run transverse striations, enclosed in a sarcolemma. Cardiac muscle fibers contain one or sometimes two nuclei and myofibrils and are separated from one another by an intercalated disk; although striated, cardiac muscle fibers branch to form an interlacing network.

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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´sinātr),
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´s),
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´rl 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

(msē´tr),
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.

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´s),
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´ylar´s 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´tōglos´l),
n the interior palate muscle that serves to raise and lower the posterior part of the tongue.

muscle, palatopharyngeus

(pal´tōferin´jēs),
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

(pltiz´m),
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.

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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.

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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.