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a sphincterlike sheet of muscle that encircles an orifice such as the mouth or the palpebral fissures.
A muscle encircling an opening.
See also: 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.
prime mover; a muscle opposed in action by another muscle, called the antagonist.
one that counteracts the action of another muscle (the agonist).
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.
part of the tunica media; smooth muscle fibers arranged in a circular pattern around the lumen.
one that has one end attached to the capsule of a joint.
1. muscles derived from the somites in the embryo.
2. the muscles around the vertebral column.
sample of living muscle obtained by excision or punch.
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.
striated muscle that inserts into the skin.
see myofiber hyperplasia.
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.
the six or seven voluntary muscles that move the eyeball: dorsal, ventral, medial and lateral recti, dorsal and ventral oblique, and retractor bulbi muscles.
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.
see muscle (above).
fixation m's, fixator m's
accessory muscles that serve to steady a part.
the biceps, semimembranosus and semitendinosus muscles. See also hamstring.
the intrinsic muscles of the eyeball.
one whose origin and insertion are both in the same part or organ, such as those entirely within the eye.
see smooth muscle (below).
layers of circular (sphincter) and radial (dilator) muscles. See also iris.
see Table 13.1H muscles of mastication.
see Table 13.1E muscles of the larynx.
see Table 13.3, 13.4 muscles of the fore- and hindlimbs.
the principal muscle of mastication. See also Table 13.1H.
see Table 13.1D muscles of the hyoid apparatus.
of striated muscle—rhabdomyoma, rhabdomyosarcoma; of plain muscle—leiomyoma, leiomyosarcoma.
see smooth muscle (below).
one that encircles a body opening, e.g. the eye or mouth.
drugs which produce neuromuscular blockade, used as muscle relaxants during surgical procedures. Include d-tubocurarine, alcuronium chloride, pancuronium, vecuronium, atracurium besylate, succinylcholine.
type 1 fibers predominate with slow contraction cycles and aerobic metabolism.
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.
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.
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.
a ringlike muscle that closes a natural orifice; called also sphincter.
sensory end-organ attached to the perimysial connective tissue of the muscle.
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.
see skeletal muscles (above).
those that assist one another in action.
a significant muscle of mastication. See also Table 13.1H.
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.
see skeletal muscle (above).
consist of type II fibers; fast contraction fibers and aerobic metabolism are characteristic.
those that normally act simultaneously and equally, as in moving the eyes.