nerve 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.

nerve fi·ber

the axon of a nerve cell, ensheathed by oligodendroglial cells in brain and spinal cord, and by Schwann cells in peripheral nerves.

nerve fiber

n.
A threadlike process of a neuron, especially the prolonged axon that conducts nerve impulses.

nerve fiber

a slender process, the axon of a neuron. Each fiber is classified as myelinated or unmyelinated. Myelinated fibers are further designated as A or B fibers. C fibers are unmyelinated. The A fibers are somatic. A alpha fibers are large fibers and transport impulses at a velocity of 60 to 100 meters per second; A beta fibers are smaller and transmit pressure and temperature impulses at a velocity of 30 to 70 meters per second. A gamma fibers transmit touch and pressure impulses. A delta fibers are the smallest and transmit impulses associated with sharp pain sensation. B fibers are more finely myelinated than A fibers. They are both afferent and efferent and are mainly associated with visceral innervation. The unmyelinated C fibers are efferent postganglionic autonomic and afferent fibers that conduct impulses of prolonged, burning pain sensation from the viscera and periphery.

nerve fi·ber

(nĕrv fībĕr)
Nerve cell axon, ensheathed by oligodendroglial cells in brain and spinal cord.

nerve

a macroscopic cordlike structure of the body, comprising a collection of nerve fibers that convey impulses between a part of the central nervous system and some other body region. For a complete list of the named nerves of the body, see Table 14.
Depending on their function, nerves are known as sensory, motor or mixed. Sensory nerves, or afferent nerves, carry information from the periphery of the body to the brain and spinal cord. Sensations of heat, cold, pressure and pain are conveyed by the sensory nerves. Motor nerves, or efferent nerves, transmit impulses from the brain and spinal cord to the periphery, especially the muscles. Mixed nerves are composed of both motor and sensory fibers, and transmit messages in both directions.
Together, the nerves make up the peripheral nervous system, as distinguished from the central nervous system, which consists of the brain and spinal cord. There are 12 pairs of cranial nerves, which carry messages to and from the brain. Spinal nerves arise from the spinal cord and pass out between the vertebrae. The various nerve fibers and cells that make up the autonomic nervous system innervate the glands, heart, blood vessels and involuntary muscles of the internal organs. For a complete list of nerves, see Table 14.

accelerator n's
the cardiac sympathetic nerves, which, when stimulated, accelerate the heart rate.
nerve biopsy
specimens taken from representative nerves by separation and removal of fascicles may provide useful information in the investigation of neuromuscular disorders or neuropathies. Consideration must be given to any resulting motor or sensory deficits that might result from the procedure. In dogs, the common peroneal, ulnar and tibial nerves are the usual sources.
nerve cuff
device used in the surgical repair of nerves to protect the site of anastomosis from an in-growth of connective tissue and to promote linear regeneration of neural elements.
depressor nerve
1. an inhibitory nerve whose stimulation depresses a motor center.
2. a nerve that lessens activity of an organ.
dermal nerve network
the organization of sensory nerve fibers to the dorsal root ganglia found in the dermis.
nerve endings
comprise afferent and efferent endings. Afferent endings transform sensations into acceptable stimuli by the CNS; include diffuse-free endings, free, modified free or encapsulated (e.g. tactile corpuscles, Krause's endbulbs, Golgi-Mazzoni corpuscles, genital corpuscles, lamellated corpuscles, Herbst corpuscles, Uffini corpuscles). Efferent endings transform nerve impulses into stimuli delivered to effector end organs; they include neuromuscular spindles, Golgi tendon organs.
encapsulated nerve endings
see nerve endings (above).
excitor nerve
one that transmits impulses resulting in an increase in functional activity.
excitoreflex nerve
a visceral nerve that produces reflex action.
nerve fiber
a process of a neuron, especially the long slender axon which conducts nerve impulses away from the cell. It may be medullated or nonmedullated.
free nerve endings
see nerve endings (above).
fusimotor n's
those that innervate the intrafusal fibers of the muscle spindle.
gangliated nerve
any nerve of the sympathetic nervous system. Called also ganglionated.
nerve gas
organophosphorus compounds specially selected for their toxicity to humans and used in chemical warfare.
nerve growth factor
a protein dimer composed of two identical polypeptide chains secreted by nerve cells and necessary for the growth and survival of certain classes of nerve cells during development.
nerve impulses
the physicochemical change in a nerve fiber's membrane which is caused by stimulation, e.g. from a stretch receptor, and which transmits a record of the sensation, or, in another case, of a motor instruction to an effector organ.
inhibitory nerve
one that transmits impulses resulting in a decrease in functional activity.
medullated nerve
myelinated nerve.
modified free nerve endings
see nerve endings (above).
myelinated nerve
one whose axons are encased in a myelin sheath.
pelvic n's
nerves of the parasympathetic outflow. See Table 14.
peripheral nerve
any nerve outside the central nervous system. Injury to a nerve causes pain initially and if tissue is destroyed, loss of function follows; signs are weakness or paralysis, atrophy, lower temperature and depressed reflexes.
pilomotor n's
those that supply the arrector muscles of hair.
pressor nerve
an afferent nerve whose impulses stimulate a vasomotor center and increases intravascular tension.
retinal nerve fiber layer
layer number 9 of the retina; axons of ganglion cells, make up bundles of nerve fibers and pass to the optic disk and lamina cribrosa; from there on they become the optic nerve.
secretory nerve
an efferent nerve whose stimulation increases glandular activity.
nerve sheath
nerve sheath tumor
neurilemmoma or schwannoma.
somatic n's
the sensory and motor nerves supplying skeletal muscle and somatic tissues.
somatic afferent n's
sensory neurons whose cell bodies reside in spinal and cranial nerve ganglia.
somatic efferent n's
motor neurons originating in ventral gray columns of the spinal cord and certain parts of the brain and are connected to striated muscles derived from embryonic somites.
spinal nerve
a segmental nerve which consists of afferent and efferent axons from its dorsal and ventral roots.
splanchnic n's
those of the blood vessels and viscera, especially the visceral branches of the thoracic, lumbar and pelvic parts of the sympathetic trunks.
nerve stimulator
an electrical device used to deliver a short stimulus to a peripheral nerve as a test of its function. It can be used to assess the effects of a neuromuscular blocking agent during clinical anesthesia.
sudomotor n's
those that innervate the sweat glands.
sympathetic n's
1. see sympathetic trunk.
2. any nerve of the sympathetic nervous system.
nerve terminal
nerve ending.
trophic nerve
one concerned with regulation of nutrition.
nerve trunk
the main body of a nerve; subsequently divides into branches.
unmyelinated nerve
one whose axons are not encased in a myelin sheath.
vasoconstrictor nerve
one whose stimulation causes narrowing of blood vessels.
vasodilator nerve
one whose stimulation causes dilatation of blood vessels.
vasomotor nerve
one concerned in controlling the caliber of vessels, whether as a vasoconstrictor or vasodilator.
vasosensory nerve
any nerve supplying sensory fibers to the vessels.
visceral afferent n's
nerves with cell bodies in spinal and cranial ganglia and which provide sensory innervation to thoracic and abdominal tissues.
visceral efferent n's
the parasympathetic component of the autonomic nervous system.
References in periodicals archive ?
Therapath's focus is on research and development in the testing services for muscle biopsy, nerve biopsy with teased fiber analysis, ocular (including optic neuritis), skin epidermal nerve fiber density, sweat gland nerve fiber density, skin biopsy for CADASIL and other storage disorders as well as brain/spinal cord specimens.
The cornea is the most densely innervated tissue in the body, so corneal nerve assessment is extremely sensitive for detecting small sensory nerve fiber damage as compared to other tests including measurement of intra-epidermal nerve fibers in the skin, notes lead investigator Joseph L.
Previous studies have shown that the appearance of white matter in magnetic resonance images depends on the angle between the nerve fibers and the direction of the very strong magnetic field used in an MRI scanner.
In MS, the immune system damages and destroys myelin, the material that surrounds and protects nerve fibers in the brain and spinal cord.
This autograft then serves as a guide for nerve fibers to cross the injury gap.
The CF represents that frequency to which the nerve fiber responds best.
At 6 months after transplantation, repeat scans in 11 of the patients who had neuropathy showed that nerve fiber density and length had improved significantly.
Dysfunction of autonomic small nerve fibers can cause motility problems in the gastrointestinal tract, as well as delayed gastric emptying.
Obrosova stated that, "The ability to increase intraepidermal nerve fiber density in diabetic rodents was previously reported for a recombinant human erythropoietin, insulin and insulin-like growth factor 1 and, recently, a glucagon-like peptide-1 receptor agonist exendin-4.
Waxman's research has shown even more potent ramifications for the role of ion channel dysfunction in MS, by demonstrating a strong association between sodium channel abnormalities and nerve fiber damage in mice with the MS-like disorder EAE.
They conducted their experiments on isolated spinal cords removed from adult guinea pigs, fusing the cut nerve fibers using a polymer called PEG.
The research team was encouraged when they found that EG can also usher long nerve fiber growth into surviving spinal cord regions beyond the end of a Schwann cell bridge.