deltoid muscle

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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.

deltoid muscle

a large, thick triangular muscle that covers the shoulder joint. It is the prime mover of arm abduction. It is also a synergist of arm flexion, extension, and medial and lateral rotation. Also called deltoideus.
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Deltoid muscle

del·toid mus·cle

(del'toyd mŭs'ĕl)
Origin, lateral third of clavicle, lateral border of acromion process, lower border of spine of scapula; insertion, lateral side of shaft of humerus a little above its middle (deltoid tuberosity); action, abduction, flexion, extension, and rotation of arm; nerve supply, axillary from fifth and sixth cervical spinal cord segments through brachial plexus.
Synonym(s): musculus deltoideus [TA] , deltoid (2) .

deltoid muscle

The large, triangular ‘shoulder-pad’ muscle which raises the arm sideways.

deltoid muscle

the muscle which covers the shoulder joint. Arises from the shoulder girdle, in continuity from the outer third of the front of the clavicle, the acromion of the scapula above the shoulder and the spine of the scapula behind it. From here the fibres converge to be inserted into the 'deltoid tuberosity' on the outer side of the humerus. A powerful abductor of the arm.

deltoid

1. triangular.
2. the deltoid muscle.

deltoid muscle
a lateral muscle of the shoulder, between the scapula and the humerus that helps flex the shoulder and abducts the arm. See also Table 13.
References in periodicals archive ?
The anterior deltoid showed similar muscle activity values of the pectoralis major for the bench press [Smith Machine, 52.
The main findings of the present study were that activation of the anterior deltoid was similar in the smith machine shoulder press, bench press and peck deck, and greater in the smitch machine shoulder press than in the other exercises; the medial deltoid showed similar activation during the reverse peck deck, seated row, free weight lateral raise and cable crossover lateral raise, and greater in the free weight lateral raise than in the other exercises; while for the posterior deltoid, the similar activation occurred during the reverse peck deck, seated row, and incline lat pull-down, and greater activation in the reverse peck deck than during other exercises.
7) The EMG activity of the anterior deltoid was greater when carrying the load in bags held by handles at the side of the body, presumably due to the need to stabilize the glenohumeral joints.
Scientific investigations indicated these activities primarily stress the anterior deltoid, triceps, and pectoral muscles within a limited movement range.
The aim of the study was to compare the electromyographic activity of the triceps brachial muscles and anterior deltoid in development exercises shoulder press and triceps bench press.
Two electrodes (a channel) for each muscle were placed on the anterior deltoid and pectoralis major for the bench press and the vastus lateralis and biceps femoris for the free squat.
1998) on the Triceps Brachii (TRICEP), Upper Trapezius (TRAPS), Anterior Deltoid (DELT), Clavicular Pectoralis (PEC), Rectus Abdominis (ABS), Rectus Femoris (FEM), and Lumbar Erector Spinae (LUMB) on the dominant side of the body.
The anterior deltoid head has shown major activity in incline condition (30) when compared with horizontal plane conditions.
Eight muscles were simulated as three lines from its origin on the scapula or clavicle to its insertion on the humerus: anterior deltoid (yellow), middle deltoid (dark green), posterior deltoid (magenta), subscapularis (light green), infraspinatus (dark blue), teres major (red), teres minor (cyan), and the clavicular portion of the pectoralis major (orange) (Fig.
Prime movers for the bench press exercise include pectoralis major, anterior deltoid, and triceps brachii muscles (Ojasto and Hakkinen, 2009).
During the isometric strength test, the maximal muscular agonist activation was evaluated using surface electromyography in the pectoralis major and anterior deltoid, and the antagonist coactivation was determined in the posterior deltoid.
Methods and Measures: sEMG was examined by cervical-brachial eight muscles (erector spinae neck, trapezius, supraspinatus, infraspinatus, pectoralis, anterior deltoid, middle deltoid and latissimus dorsi) of the right shoulder of 16 subjects (8 men and 8 women).

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