muscle fiber

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fiber

 [fi´ber]
1. an elongated threadlike structure.
A f's myelinated 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.
accelerating f's (accelerator f's) adrenergic fibers that transmit the impulses that accelerate the heart beat.
adrenergic f's nerve fibers of the sympathetic nervous system that liberate norepinephrine (and possibly small amounts of epinephrine) at a synapse when a nerve impulse passes.
alpha f's motor and proprioceptive fibers of the A type having conduction velocities of 70 to 120 meters per second and ranging from 13 to 22 micrometers in diameter.
arcuate f's any of 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 f's nerve fibers that interconnect portions of the cerebral cortex within a hemisphere. Short association fibers interconnect neighboring gyri; long fibers interconnect more widely separated gyri and are arranged into bundles or fasciculi.
B f's myelinated preganglionic autonomic axons having a fiber diameter less than 3 μm and a conduction velocity of 3 to 15 meters per second.
beta f's touch and temperature fibers of the A type having conduction velocities of 30 to 70 meters per second and ranging from 8 to 13 micrometers in diameter.
C f's postganglionic unmyelinated fibers of the autonomic nervous system; also, the unmyelinated fibers at the dorsal roots and at free nerve endings having a diameter of 0.3 to 1.3 μm and a conduction velocity of 0.6 to 2.3 meters per second.
cholinergic f's nerve fibers such as the parasympathetic fibers that liberate acetylcholine at a synapse when a nerve impulse passes.
collagen f's (collagenous f's) the soft, flexible, white fibers that 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) that show a characteristic crossbanding with a major periodicity of 65 nm.
Corti's f's pillar cells.
crude fiber the fiber that remains after food is digested with alkali and acid, which destroys all soluble and some insoluble fiber. It is mainly lignin and cellulose.
depressor f's afferent nerve fibers that when stimulated reflexly cause diminished vasomotor tone and thus decreased arterial pressure.
dietary fiber that portion of ingested foodstuffs that cannot be broken down by intestinal enzymes and juices and, therefore, passes through the small intestine and colon undigested. It is composed of cellulose (which is the “skeleton” of plants), hemicellulose, gums, lignin, pectin, and other carbohydrates indigestible by humans. Dietary fiber is not to be confused with crude fiber, which is the term used in the USDA Handbook and other tables listing the composition of foods. Crude fiber is mainly lignin and cellulose and is the residue remaining after a food has been subjected to a standardized treatment with dilute acid and alkali. Crude fiber measurements usually underestimate actual total dietary fiber by at least 50 per cent.

Vegetables, cereals, and fruits are the main sources of dietary fiber. Although bran is advertised as an excellent source of fiber, it is not unique nor is it as nutritious as fruits and vegetables and some other whole unprocessed cereals. The typical diet in Western countries contains 10 to 30 grams of dietary fiber.

The primary effects of dietary fiber are to increase the bulk of the stool and make it softer by taking up water as it passes through the colon, and to absorb organic wastes and toxins and carry them out of the intestinal tract. The increase in stool bulk hastens the passage of feces and may reduce the length of time the intestinal wall is exposed to toxic substances.
Benefits of a High Fiber Diet. Dietary fiber is helpful in the treatment and prevention of uncomplicated constipation. Unlike strong laxatives, it presents no problems when taken on a long-term basis. Metamucil, a medicinal fecal softener, is made from seed husks and is often prescribed for persons having problems with normal bowel activity. Hemorrhoids are aggravated by straining on defecation, and so there is some basis for recommending a high fiber diet for persons who have this condition.

The symptoms of diverticular disease, which is an outpouching of the wall of the colon with subsequent inflammation, are relieved by a high fiber diet. There is evidence to support the theory that the more rapid passage of softer stools through the colon decreases the pressure exerted against its walls and thereby prevents formation of diverticula.

The symptoms of irritable bowel syndrome often can be mitigated by fiber. The bulk of fiber keeps the colon mildly distended, thus preventing the development of pockets of high pressure that cause spasm. However, inflammatory bowel disease in which there is a narrowing of the bowel, as in some cases of crohn's disease, can be worsened by more roughage in the intestinal tract.

Fiber does have the capacity to unite with intestinal bile salts and dietary cholesterol, preventing their absorption from the gut and hastening their elimination via the intestinal tract. Because of these properties, fiber has been advocated as a preventive measure against the formation of gallstones and the production of atherosclerotic plaques in the blood vessels.

In diabetes mellitus, fiber, when eaten with other foods, somewhat reduces the rise in blood glucose that occurs after eating. Fiber slows the rate of carbohydrate breakdown and absorption from the intestinal tract. The American Cancer Society suggests a diet rich in fiber as a way to lower the incidence of certain kinds of cancer, particularly colorectal cancer.

Some people may have difficulties with a high fiber diet. It can produce abdominal pain, bloating, flatus, and diarrhea. These side effects can be controlled if the fiber is introduced to the diet in small amounts and with an increase in fluid intake. Excessive amounts of fiber can also impair absorption of essential minerals.
elastic f's yellowish fibers of elastic quality traversing the intercellular substance of connective tissue.
gamma f's fibers that conduct touch and pressure impulses and innervate the intrafusal fibers of the muscle spindle; they conduct at velocities of 15 to 40 meters per second and range from 3 to 7 μm in diameter.
gray f's unmyelinated 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. Its actions include increasing fecal bulk and decreasing free radicals in the gastrointestinal tract.
intrafusal f's modified muscle fibers which, surrounded by fluid and enclosed in a connective tissue envelope, compose the muscle spindle.
light f's muscle fibers poor in sarcoplasm and more transparent than dark fibers.
Mahaim f's short direct connections between the lower atrioventricular node or bundle of His and the ventricular septum, resulting in preexcitation of the ventricular septum and a delta wave. Only right sided connections have been described.
medullated f's (medullated nerve f's) myelinated fibers.
motor f's nerve fibers transmitting motor impulses to a muscle fiber.
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.
muscle f's, fast twitch paler-colored muscle fibers of larger diameter than slow twitch fibers, and having less sarcoplasm and more prominent cross-striping; used for forceful and rapid contractions over short periods of time.
muscle f's, slow twitch small dark muscle fibers rich in mitochondria, myoglobin, and sarcoplasm and with only faint cross-striping; designed for slow but repetitive contractions over long periods of time.
myelinated f's grayish white nerve fibers encased in a myelin sheath; see myelin.
nerve fiber a slender process of a neuron, especially the prolonged axon that conducts nerve impulses away from the cell; classified as either myelinated fibers or unmyelinated fibers according to whether they have or do not have a myelin sheath.
nonmedullated f's unmyelinated fibers.
osteogenetic f's (osteogenic f's) precollagenous fibers formed by osteoclasts and becoming the fibrous component of bone matrix.
postganglionic f's nerve fibers passing to involuntary muscle and gland cells, the cell bodies of which lie in the autonomic ganglia.
preganglionic f's nerve fibers passing to the autonomic ganglia, the cell bodies of which lie in the brain or spinal cord.
pressor f's afferent nerve fibers that when stimulated reflexly cause or increase vasomotor tone and thus increase arterial pressure.
projection f's bundles of axons that connect the cerebral cortex with the subcortical centers, brain stem, and spinal cord.
Purkinje f's modified cardiac fibers in the subendocardial tissue that constitute the terminal ramifications of the conducting system of the heart. The term is sometimes used loosely to denote the entire system of conducting fibers.
radicular f's fibers in the roots of the spinal nerves.
ragged red f's muscle fibers characterized by large collections of structurally abnormal mitochondria below the sarcolemmal surface and within the fiber itself that stain red; seen in mitochondrial myopathy and certain other myopathic disorders.
reticular f's 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 skin, and elsewhere.
Sharpey's f's
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. It acts to decrease the rate of stomach emptying and increase transit time through the intestine, and also binds bile acids, increasing their excretion. Soluble fiber appears to specifically lower levels of low-density lipoproteincholesterol.
somatic f's (somatic nerve f's) nerve fibers, afferent or efferent, that stimulate or activate skeletal muscle and somatic tissues.
spindle f's the microtubules radiating from the centrioles during mitosis and forming a spindle-shaped configuration.
unmyelinated f's nerve fibers that lack a myelin sheath; see myelin.
visceral f's (visceral nerve f's) nerve fibers, afferent or efferent, that stimulate or activate smooth muscle and glandular tissues.

muscle fiber

n.
A muscle cell, especially one of the cylindrical, multinucleate cells that make up skeletal muscles and and are composed of numerous myofibrils that contract when stimulated.

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.

mus·cle fi·ber

(mŭs'ĕl fī'bĕr)
Classification of muscle fiber is based on contractile and metabolic characteristics. Slow-twitch (type I) fibers contract slowly and develop relatively low tension; they display high oxidative and low glycolytic capacity associated with endurance performance. Fast-twitch (type II) fibers have rapid speed of activation and develop high tension; they display low oxidative and high glycolytic capacity associated with strength and power performance.

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.