nerve fiber

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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nerve fiber

n.

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

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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.

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fiber [fi´ber]

1. an elongated threadlike structure.

2. dietary fiber.

3. nerve f.

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.

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nerve,

n a cordlike structure that conveys impulses between a part of the central nervous system and some part of the body and consists of an outer connective tissue sheath and bundles of nerve fibers. See also each of the individual nerves of the head and neck as they are listed.

nerve, abducent (VI),

n the sixth cranial nerve; a small, completely motor nerve arising in the pons, supplying the lateral rectus muscle of the eye.

nerve, accessory,

n See nerve, spinal accessory.

nerve, acoustic (VIII),

n the eighth cranial nerve; the vestibulocochlear nerve; a sensory nerve consisting of a vestibular portion and an auditory (or cochlear) portion.

nerve(s), afferent, in pulp,

n any nerve that originates as a terminal free nerve ending in the dental pulp tissue and travels to the second and third divisions (maxillary nerve and mandibular nerve) of the cranial trigeminal nerve (cranial nerve V).

nerve, alveolar,

n afferent nerves that convey impulses from the pulp tissue and periodontium of the maxillary teeth to the maxillary division of the cranial trigeminal nerve.

nerve, anterior superior alveolar,

n alveolar nerve that conveys impulses from the pulp tissue and periodontium of the maxillary anterior teeth to the infraorbital nerve.

nerve, auriculotemporal

n a nerve that transmits feeling from the external ear, scalp, and parotid salivary gland to the mandibular division of the cranial trigeminal nerve.

nerve, branchial,

n one of five cranial nerves that supply the derivatives of the branchial arches: trigeminal (V), facial (VII), glossopharyngeal (IX), vagus (X), and spinal accessory (XI). Each branchial nerve may have a variety of functions, including visceral motor and visceral and somatic sensory functions.

nerve, buccal (long),

n afferent nerve that conveys impulses from the facial periodontium of the mandibular molars and gingiva to the mandibular division of the cranial trigeminal nerve.

nerve, chiasma, optic,

n the decussation, or crossing, of optic nerve fibers from the medial side of the retina on one side to the opposite side of the brain.

nerve, chorda tympani

n a parasympathetic and special sensory branch of the facial nerve supplying the submandibular and sublingual glands and the anterior two thirds of the tongue (taste).

nerve, cochlear

n one of the two major branches of the eighth cranial nerve; a special sensory nerve for the sense of hearing that transmits impulses from the organ of Corti to the brain.

nerve, cranial,

n any one of 12 paired nerves, classified in three sets, arising directly in the brain and supplying various tissues of the head and neck. The cranial nerves are the special somatic sensory nerves: olfactory (I), optic (II), and vestibulocochlear (acoustic) (VIII); the somatic motor nerves: oculomotor (III), trochlear (IV), abducent (VI), and hypoglossal (XII); and the branchial nerves: trigeminal (V), facial (VII), glossopharyngeal (IX), vagus (X), and spinal accessory (XI).

nerve, deep temporal,

n an anterior and a posterior nerve that branch away from the mandibular nerve of the trigeminal nerve and extend deep into the temporalis muscle, which is used during mastication.

nerve degeneration,

n the reversion to a less organized and functioning state, usually detected by the loss of ability to conduct or transmit nerve impulses. Advanced degeneration might show cellular decomposition.

nerve ending,

n the terminal of a nerve fiber, usually in synapse with another fiber or in a sensory organ.

nerve, facial (VII),

n the seventh cranial nerve; a mixed nerve supplying motor fibers to the facial muscles, the stapedius, and posterior body of the digastric; sensory fibers from the taste buds in the anterior two thirds of the tongue (via the chorda tympani); and general visceral autonomic fibers for the submandibular and sublingual salivary glands. It travels unilaterally over the face and at one point is located in the parotid salivary gland, which it does not serve. However, pain in the parotid gland indicates a glandular malignancy, and complications with an inferior nerve block can also result from its location there.

The cranial nerves.

nerve fiber,

n a slender process of a neuron, usually the axon. Each fiber is classified as myelinated or unmyelinated.

nerve, frontal,

n afferent nerve from the union of the superorbital and supratrochlear nerves that carries information from the forehead, scalp, nose, and upper eyelids to the ophthalmic division of the cranial trigeminal nerve.

nerve, glossopharyngeal (IX)

n the ninth cranial nerve; a mixed motor and sensory nerve arising in the medulla and supplying motor efferents to stylopharyngeal muscles and other pharyngeal muscles; visceral motor efferents via the otic ganglion for the parotid gland; special visceral afferents from the taste buds in the posterior third of the tongue; and general sensory afferents from the pharynx and posterior aspects of the oral cavity. It is essential to the sense of taste.

nerve, greater (anterior) palatine,

n the nerve originating in the pterygopalatine ganglion that supplies the hard palate, part of the soft palate, and its associated lingual mucosa.

nerve, greater petrosal

n one of the two nerves that branch off of the facial nerve and help control the muscles used in facial expression; this nerve also carries impulses to the lacrimal gland and the nasal cavity, and to and from the palate. The nerve has both afferent and efferent fibers.

nerve, hypoglossal (XII),

n the twelfth cranial nerve; a motor nerve that arises in the medulla and supplies extrinsic and intrinsic muscles of the tongue. Each nerve has four major branches, communicates with the vagus nerve, and connects to the nucleus XII in the brain.

nerve, incisive,

n afferent nerve that merges with the mental nerve to later create the inferior alveolar nerve in the mandibular canal. This nerve transmits feeling from the pulp tissue and facial periodontium of the mandibular anterior teeth and premolars to the mandibular division of the cranial trigeminal nerve.

nerve, inferior alveolar,

n a motor and general sensory branch of the mandibular nerve, with mylohyoid, inferior dental, mental, and inferior gingival branches.

nerve, infraorbital,

n afferent nerve that enters through the infraorbital foramen and canal to merge with the maxillary branch of the cranial trigeminal nerve.

nerve, intermediate,

n the parasympathetic and special sensory division of the facial nerve with chorda tympani and greater petrosal branches.

nerve, lacrimal,

n afferent nerve that is part of the ophthalmic division of the cranial trigeminal nerve and controls secretions in the upper eyelid, lacrimal gland, and the conjunctiva.

nerve, lingual,

n a general sensory branch of the mandibular nerve having sublingual and lingual branches and connections with the hypoglossal nerve and chorda tympani.

nerve, mandibular,

n the mandibular division of the trigeminal nerve, arising in the trigeminal ganglion and supplying general sensory and motor fibers via mesenteric, pterygoid, buccal, auriculotemporal, deep temporal, lingual, inferior alveolar, and meningeal branches.

nerve, maxillary,

n the maxillary division of the trigeminal nerve arising in the trigeminal ganglion and supplying general sensory fibers via zygomatic, posterosuperior alveolar, infraorbital, pterygopalatine, and nasopalatine branches.

nerve, mental,

n a nerve that branches off the inferior alveolar nerve, emerging from the mandible through the mental foramen and branching further to provide sensory innervation to the tissues of the chin and lower lip and the labial mucosa of the mandibular premolars and anterior teeth.

nerve, middle superior alveolar,

n alveolar nerve that conveys impulses from the pulp tissue and periodontium of the gingiva and the maxillary premolar teeth to the infraorbital nerve. This nerve is not always present in all persons. If not present, the premolars are innervated by the posterior superior alveolar nerve.

nerve, mylohyoid,

n a branch of the mandibular division of the cranial trigeminal nerve that serves the mylohyoid and digastric muscles of the oral cavity. It is thought to be a possible alternative innervation for the pulp tissues of the mandibular first molar in some cases.

nerve, nasociliary

n one of three branches of the cranial trigeminal nerve that controls parts of the eyes, nasal cavity, and paranasal sinuses.

nerve, nasopalatine

n afferent nerve that conveys impulses from the lingual periodontium of the maxillary anterior teeth bilaterally and the anterior hard palate to the maxillary division of the cranial trigeminal nerve.

nerve, oculomotor (III)

n the third cranial nerve; primarily a motor nerve arising from the midbrain and supplying motor efferents to the superior rectus, medial rectus, inferior rectus, and inferior oblique eye muscles, as well as autonomic fibers via the ciliary ganglion to the ciliary body and the iris.

nerve, olfactory (I)

n the first cranial nerve; a special sensory nerve for the sense of smell.

nerve, ophthalmic

n the ophthalmic division of the trigeminal nerve, arising in the trigeminal ganglion and supplying general sensory fibers via the frontal, lacrimal, and nasociliary branches.

nerve, optic (II),

n the second cranial nerve; a special sensory nerve for vision. It consists mainly of coarse, myelinated fibers that arise in the retinal ganglionic layer of the eye, traverse the thalamus, and connect with the visual cortex of the brain.

nerve, palatine,

n the two afferent nerves of the maxillary division of the cranial trigeminal nerve. The greater palatine nerve innervates the posterior hard palate and lingual periodontium of the maxillary molar teeth, while the lesser palatine nerve innervates the soft palate and palatine tonsillar tissue.

nerve, posterior superior alveolar,

n alveolar nerve that conveys impulses from the maxillary sinus, gingiva, pulp tissue, and periodontium of the maxillary molar teeth to the infraorbital nerve or to the maxillary nerve directly.

nerve regeneration,

n the reconstruction and renewal of cell structure and function; generally restricted to myelinated nerve fibers.

nerve repositioning,

n the surgical redirecting of the inferior alveolar and/or mental nerve to allow longer implants to be placed in a mandible that has extensive deterioration of the posterior ridge. Some temporary or long-term loss of sensation to the lip, tongue, chin and/or gingival tissue may result. Also known as
nerve lateralization and
nerve transpositioning.

nerve(s), somatic motor,

n (cranial), the somatic motor nerves–oculomotor (III), trochlear (IV), abducent (VI), and hypoglossal (XII)–largely comparable to the ventral motor roots of the spinal nerves. They are composed almost entirely of somatic motor fibers that emerge ventrally from the brainstem. Their arrangement is closely correlated with the distribution of the myotomes in the head. The oculomotor, trochlear, and abducent nerves, which supply the eye musculature, have the same myotomic origin and arrangement as the somatic muscles of the trunk and extremities.

nerve(s), special somatic sensory,

n the structural arrangements from typical sensory nerves by which the three main sense organs, nose, eyes, and ears, are innervated. The sensory nerves are the olfactory (I), optic (II), and vestibulocochlear (acoustic) nerves (VIII).

nerve(s), spinal,

n any one of 31 pairs of mixed peripheral nerves (8 cervical, 12 thoracic, 5 lumbar, 5 sacral, and 1 coccygeal) that are connected segmentally with the spinal cord, dorsal sensory trunk, and ventral motor root.

nerve, spinal accessory (XI),

n the eleventh cranial nerve; a motor nerve that derives its origin in part from the medulla and in part from the cervical spinal cord. Its internal ramus joins with the vagus nerve to supply some of the muscles of the larynx. Its external ramus joins with the spinal nerves to supply the sternocleidomastoid and trapezius muscles. The nerve and its relationship to head posture is important in maintaining stable occlusal relationships of vertical dimension and centric relation.

nerve, tensor tympani,

n a small motor branch of the mandibular nerve.

nerve, trigeminal (V)

n the fifth cranial nerve; a mixed motor and sensory nerve connected with the pons through three roots (motor, proprioceptive, and large sensory), the latter root expanding into the trigeminal ganglion, from which arise the ophthalmic, masseteric, and mandibular divisions. It serves the muscles of mastication and cranial muscles through its motor root and serves the teeth, tongue, and oral cavity and most of the facial skin through its sensory root.

nerve, trochlear (IV)

n the fourth cranial nerve; a small motor nerve arising ventrally in the midbrain and supplying the inferior oblique muscle of the eye.

nerve trunk,

n a particularly sizeable bundle of axons or nerve fibers.

nerve, vagus (X)

n the tenth cranial nerve; a mixed parasympathetic, visceral, afferent, motor, and general sensory nerve with laryngeal, pharyngeal, bronchial, esophageal, gastric, and many other branches.

nerve, vestibular (VIII),

n one of the two major branches of the eighth cranial nerve; a special sensory nerve for the sense of balance and the transmission of space-orientation impulses from the semicircular canals to the brain.

nerve, vestibulocochlear (VII),

n the seventh cranial nerve; acoustic nerve; a sensory nerve consisting of a vestibular portion and an auditory, or cochlear, portion.

nerve, zygomatic

n the afferent nerve of the maxillary division of the cranial trigeminal nerve that serves the skin of the cheek and temple. It also innervates the lacrimal gland.

nerve(s), dentinal,

n any of the afferent or sensory neurons associated with the odontoblastic processes in the dentinal tubules and the attached cell body of the odontoblasts within the pulp tissue. These nerves may allow for an awareness of pain due to their monitoring of environmenal changes within the dentin. There is some controversy about their overall location in the dentin tubule (full length, partial, or not at all).

nerves, efferent,

n motor nerves that carry impulses from the brain or spinal cord toward the periphery of the body to activate muscles, usually in response to impulses received from sensory nerves.

nerve(s), periodontal ligament,

n the sympathetic fibers of the autonomic nervous system with enclosed nerve endings that control blood flow within the vessels and register pressure changes. Sensory or afferent fibers with free nerve endings cause an awareness of pain.

nerve(s), pulp,

n the sympathetic fibers of the autonomic nervous system located within the tissue that control blood flow within the vessels. Sensory or afferent fibers with free nerve endings in close proximity to the odontoblasts may cause an awareness of pain.

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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.

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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

see neurilemma.

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.