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fiber (fI´ber)

A slender thread or filament. 1. Extracellular filamentous structures such as collagenic or elastic connective tissue f.'s. 2. The nerve cell axon with its glial envelope. 3. Elongated, hence threadlike, cells such as muscle cells and the epithelial cells composing the major part of the eye lens.fibra [NA], fibre; [L. fibra]
A f.'s myelinated nerve f.'s in somatic nerves, measuring 1 to 22 mum in diameter, conducting nerve impulses at a rate of 6 to 120 m/sec.
accelerator f.'s postganglionic sympathetic nerve f.'s originating in the superior, middle, and inferior cervical ganglia of the sympathetic trunk, conveying nervous impulses to the heart that increase the rapidity and force of the cardiac pulsations.augmentor f.'s;
adrenergic f.'s nerve f.'s that transmit nervous impulses to other nerve cells (or smooth muscle or gland cells) by the medium of the adrenaline-like transmitter substance norepinephrine (noradrenaline).
afferent f.'s those that convey impulses to a ganglion or to a nerve center in the brain or spinal cord.
alpha f.'s large somatic motor or proprioceptive nerve f.'s conducting impulses at rates near 100 m/sec.
anastomosing f.'s , anastomotic f.'s individual f.'s passing from one nerve trunk or muscle bundle to another.
arcuate f.'s nervous or tendinous f.'s passing in the form of an arch from one part to another. See arcuate f.'s of cerebrum, external arcuate f.'s, internal arcuate f.'s.
arcuate f.'s of cerebrum short association fibers that connect adjacent gyri in the cerebral cortex.fibrae arcuatae cerebri [NA] ;
argyrophilic f.'s reticular connective tissue f.'s that react with silver salts and appear black microscopically.
association f.'s nerve f.'s interconnecting subdivisions of the cerebral cortex of the same hemisphere or different segments of the spinal cord on the same side.endogenous f.'s, intrinsic f.'s;
astral f.'s f.'s (fibrils) radiating from the centrosphere toward the periphery of the cell as seen with a light microscope; revealed as microtubules under the electron microscope. Cf. kinetochore f.'s, polar f.'s.
augmentor f.'s accelerator f.'s
B f.'s myelinated f.'s autonomic nerves, with a diameter of 2 mum or less, conducting at a rate of 3 to 15 m/sec.
Bergmann's f.'s filamentous glia f.'s traversing the cerebellar cortex perpendicular to the surface.
beta f.'s nerve f.'s having conduction velocities of about 40 m/sec.
C f.'s unmyelinated f.'s, 0.4 to 1.2 mum in diameter, conducting nerve impulses at a velocity of 0.7 to 2.3 m/sec.
cerebellohypothalamic f.'s nerve f.'s originating from cells of the cerebellar nuclei and projecting, via the superior cerebellar peduncle, to the contralateral hypothalamus, mainly its dorsal, lateral, and posterior areas and dorsomedial nucleus.
cerebellospinal f.'s See fastigiospinal f.'s.
cholinergic f.'s nerve f.'s that transmit impulses to other nerve cells, muscle fibers, or gland cells by the medium of the transmitter substance acetylcholine.
chromatic f. chromonema
circular f.'s the circular f.'s of the ciliary muscle.fibrae circulares [NA], Müller's f.'s (1), Müller's muscle (2), Rouget's muscle;
climbing f.'s nerve f.'s in the cerebellar cortex that synapse upon smooth branchlets of Purkinje cell dendrites.
collagen f. , collagenous f. an individual f. that varies in diameter from less than 1 mum to about 12 mum and is composed of fibrils; the f.'s, which are usually arranged in bundles, undergo some branching and are of indefinite length; chemically the f. is a glycoprotein, collagen, which yields gelatin upon boiling; they make up the principal element of irregular connective tissue, tendons, aponeuroses, and most ligaments, and occur in the matrix of cartilage and osseous tissue.white f. (2) ;
commissural f.'s nerve f.'s crossing the midline and connecting two corresponding parts or regions of the nervous system.
cone f. a part of the cone cell of the retina; the inner cone f. is a slender axon-like part of the cone extending from the cell body to the pedicle located in the outer plexiform layer of the retina; in the outer fovea, where the cones are much elongated, they narrow to an outer cone f. , located between the inner segment and the cell body.
corticobulbar f.'s nerve f.'s projecting from the motor and somatic sensory cortex to the rhombencephalon; included in this corticofugal f. system are corticoreticular f.'s terminating in the reticular formation of the rhombencephalon, and corticonuclear f.'s to the motor nuclei innervating the musculature of the face, tongue, and jaws, and to some f.'s of the rhombencephalic sensory relay nuclei. See also corticobulbar tract.
corticonuclear f.'s descriptive term connotating f.'s from a cortical structure (cerebral or cerebellar) passing to subcortical cell groups; f.'s comprising the tractus corticobulbaris; cerebellar corticonuclear f.'s (Purkinje cell axons to the cerebellar nuclei).fibrae corticonucleares [NA] ;
corticopontine f.'s the f.'s that compose the corticopontine tract.fibrae corticopontinae;
corticoreticular f.'s corticofugal f.'s distributed to the reticular formation of the mesencephalon and rhombencephalon. See also corticobulbar f.'s.fibrae corticoreticulares [NA] ;
corticorubral f.'s nerve f.'s projecting from the cerebral cortex (primarily precentral and premotor regions) to the red nucleus of the midbrain.
corticospinal f.'s pyramidal f.'s
corticothalamic f.'s a general term designating nerve f.'s originating from any area of the cerebral cortex and terminating in the nuclei of the thalamus.
dentatorubral f.'s nerve f.'s arising in the dentate nucleus of the cerebellum and projecting, via the superior cerebellar peduncle and its decussation, to the contralateral red nucleus of the midbrain.fibrae dentatorubrales;
dentatothalamic f.'s nerve f.'s projecting from the dentate nucleus of the cerebellum to the contralateral thalamus via the superior cerebellar peduncle (and its decussation); enter the thalamus as one component of the thalamic fasciculus.
dentinal f.'s , dental f.'s 1. the processes of the pulpal cells, the odontoblasts, which extend in radial fashion through the dentin to the dentoenamel junction and are contained within the dentinal tubules;Tomes' f.'s; 2. the intertubular fine collagenous f.'s that with the dentinal ground substance infiltrated with calcium salts constitutes the dentinal matrix.
depressor f.'s sensory nerve f.'s having pressure-sensitive nerve endings in the wall of certain arteries capable of activating blood pressure-lowering brainstem mechanisms when stimulated by an increase in intra-arterial pressure.
dietary f. the plant polysaccharides and lignin that are resistant to hydrolysis by the digestive enzymes in humans.
efferent f.'s those f.'s conveying impulses to effector tissues (muscle: smooth, cardiac or striated; or glands) in the periphery; those f.'s exiting a specific cell group (i.e., efferent fibers of the basilar pons), used in reference to a cell group.
elastic f.'s f.'s that are 0.2 to 2 mum in diameter but may be larger in some ligaments; they branch and anastomose to form networks and fuse to form fenestrated membranes; the f.'s and membranes consist of microfibrils about 10 nm wide and an amorphous substance containing elastin.yellow f.'s;
enamel f.'s prismata adamantina, under prisma
endogenous f.'s association f.'s
exogenous f.'s nerve f.'s by which a given region of the central nervous system is connected with other regions; the term applies to both afferent and efferent fiber connections.
external arcuate f.'s they include: 1) dorsal external arcuate f.'s that arise from cells in the accessory or lateral cuneate nucleus and pass to the cerebellum; 2) ventral external arcuate f.'s that arise from the arcuate nuclei at the base of the medulla oblongata and pass around the lateral surface of the medulla; both enter the cerebellum as components of the restiform portion of the inferior cerebellar peduncle.fibrae arcuatae externae [NA] ;
fastigiobulbar f.'s nerve f.'s projecting from the fastigial nuclei of the cerebellum to the brain stem; crossed and uncrossed f.'s that terminate mainly in the vestibular and reticular nuclei, and in the medial accessory olivary nucleus.
fastigiospinal f.'s crossed descending f.'s originating in the fastigial nucleus of the cerebellum and ending in the spinal cord gray matter at cervical, and possibly lower, levels.
gamma f.'s nerve f.'s that have a conduction rate of about 20 m/sec. See also gamma efferent.
Gerdy's f.'s superficial transverse metacarpal ligament
Gratiolet's f.'s optic radiation
gray f.'s unmyelinated f.'s
hypothalamocerebellar f.'s nerve f.'s originating from cells in the hypothalamus and projecting to the cerebellar cortex and nuclei.
inhibitory f.'s nerve f.'s that inhibit the activity of the nerve cells with which they have synaptic connections, or of the effector tissue (smooth muscle, heart muscle, glands) in which they terminate.
intercolumnar f.'s intercrural f.'s
intercrural f.'s horizontal arched fibers that pass from the inguinal ligament across the medial and lateral crura of the superficial inguinal ring.fibrae intercrurales [NA], intercolumnar fasciae, intercolumnar f.'s;
internal arcuate f.'s f.'s that arise in the cuneate and gracile nuclei, pass in a curving course across the midline of the medulla oblongata, and form the contralateral medial lemniscus; also designates other f.'s such as those of the olivocerebellar tract that arch through the substance of the medulla and form sensory decussation.fibrae arcuatae internae [NA] ;
intrafusal f.'s muscle f.'s present within a neuromuscular spindle.
intrinsic f.'s association f.'s
James f.'s atrio-His bundle connections thought to be the basis for the short P-R interval syndrome; these f.'s should be distinguished from the internodal tracts of the atrium, sometimes referred to as "James tracts."James tracts;
kinetochore f.'s f.'s of the mitotic spindle attached to the centromere and extending toward the poles. Cf. astral f.'s, polar f.'s.
Korff's f.'s argyrophilic f.'s that pass between odontoblasts at the periphery of the dental pulp and fan out into the dentin.
Kühne's f. artificial muscle f. made by filling the intestine of an insect with a growth of myxomycetes; used to demonstrate the contractility of protoplasm.
f.'s of lens the elongated cells of ectodermal origin forming the substance of the crystalline lens of the eye.fibrae lentis [NA] ;
Mahaim f.'s paraspecific f.'s originating from the A-V node, the His bundle, or the bundle branches and inserting into the ventricular myocardium; they are potential pathways for reentrant dysrhythmias.nodoventricular f.'s;
medullated nerve f. myelinated nerve f
meridional f.'s the longitudinal fibers of the ciliary muscle.fibrae meridionales [NA] ;
mossy f.'s highly branched nerve f.'s in the cerebellar cortex that terminate in rosette formations and synapse upon granule cell dendrites.
motor f.'s nerve f.'s that transmit impulses that activate effector cells, e.g., in muscle or gland tissue.
Müller's f.'s 1. circular f.'s 2. sustentacular neuroglial cells of the retina, running through the thickness of the retina from the internal limiting membrane to the bases of the rods and cones where they form a row of junctional complexes.Müller's radial cells, sustentacular f.'s of retina;
myelinated nerve f. an axon enveloped by a myelin sheath formed by oligodendroglia cells (in brain and spinal cord) or Schwann cells (in peripheral nerves).medullated nerve f;
Nélaton's f.'s Nélaton's sphincter
nerve f. the axon of a nerve cell, ensheathed by oligodendroglia cells in brain and spinal cord, and by Schwann cells in peripheral nerves.
nodoventricular f.'s Mahaim f.'s
nonmedullated f.'s unmyelinated f.'s
nuclear bag f. the largest type of intrafusal muscle f.'s in a neuromuscular spindle, containing a central aggregation of nuclei (nuclear bag).
nuclear chain f. the shortest and most numerous type of intrafusal muscle f.'s in a neuromuscular spindle, containing a single row of centrally positioned nuclei.
nucleocortical f.'s general term for projections from a nucleus to an overlying cortical structure; specifically used to designate axons of cerebellar nuclear cells that project to the cerebellar cortex (cerebellar nucleocortical f.'s) where they end as mossy f.'s.
oblique f.'s of stomach the smooth muscle fibers of the innermost layer of the muscular coat of the stomach; the fibers occur chiefly at the cardiac end of the stomach and spread over the anterior and posterior surfaces.fibrae obliquae gastrici [NA] ;
olivocochlear f.'s olivocochlear bundle
osteocollagenous f.'s fine collagenous f.'s in the matrix of osseous tissue.
osteogenetic f.'s the f.'s in the osteogenetic layer of the periosteum.
pectinate f.'s pectinate muscles, under muscle
perforating f.'s bundles of collagenous f.'s that pass into the outer circumferential lamellae of bone or the cementum of teeth.Sharpey's f.'s;
periodontal ligament f.'s the collagen f.'s, running from the cementum to the alveolar bone, that suspend a tooth in its socket; they include apical, oblique, horizontal, and alveolar crest f.'s, indicating that the orientation of the f.'s varies at different levels.
periventricular f.'s a heterogeneous system of thin nerve f.'s in the periventricular gray matter of the hypothalamus; the dorsal longitudinal fasciculus is a caudal continuation of the system.fibrae periventriculares [NA] ;
pilomotor f.'s nerve f.'s that innervate the erector muscles of hair follicles responsible for piloerection.
polar f.'s >those f.'s of the mitotic spindle extending from the two poles of the spindle toward the equator. Cf. astral f.'s, kinetochore f.'s.
postganglionic f.'s a f. whose cell body is located in an autonomic (motor) ganglion and whose peripheral process will terminate on smooth muscle, cardiac muscle, or glandular epithelium; associated with sympathetic or parasympathetic parts of the autonomic nervous system.
precollagenous f.'s immature, argyrophilic f.'s.
preganglionic f.'s a f. whose cell body is located in an autonomic nucleus in the spinal cord or brain stem and whose axon terminates in an autonomic (motor) ganglion; found in nerves conveying sympathetic or parasympathetic f.'s.
pressor f.'s sensory nerve f.'s whose stimulation causes vasoconstriction and rise of blood pressure.
projection f.'s nerve f.'s connecting the cerebral cortex with other centers in the brain or spinal cord; fibers arising from cells in the central nervous system that pass to distant loci.
Prussak's f.'s elastic and connective tissue f.'s bounding the pars flaccida membranae tympani.
Purkinje's f.'s interlacing f.'s formed of modified cardiac muscle cells with central granulated protoplasm containing one or two nuclei and a transversely striated peripheral portion; they are the terminal ramifications of the conducting system of the heart found beneath the endocardium of the ventricles. See also conducting system of heart.
pyramidal f.'s the f.'s that compose the pyramidal tract (corticospinalis).fibrae corticospinales [NA], corticospinal f.'s, fibrae pyramidales;
raphespinal f.'s nerve f.'s originating from cells of the nuclei raphe magnus, pallidus, and obscurus of the pons and medulla and terminating in the spinal cord gray matter; f.'s involved in the descending inhibition of nociceptive input in the dorsal (posterior) horn; they contain serotonin.
red f.'s red striated muscle f.'s that are rich in sarcoplasm, myoglobin, and mitochondria; they are smaller in diameter and contract more slowly than white f.'s.
Reissner's f. a rodlike, highly refractive f. running caudally from the subcommissural organ throughout the length of the central canal of the brainstem and spinal cord.
Remak's f.'s unmyelinated f.'s
reticular f.'s the collagen (type III) f.'s forming the distinctive loose connective tissue stroma of embryonic tissues, mesenchyme, red pulp of the spleen, cortex and medulla of lymph nodes, and the hematopoietic compartments of bone marrow and comprising a substantial portion of the collagen f.'s of the skin, blood vessels, synovial membrane, uterine tissue, and granulation tissue; characterized by its organization as a reticular meshwork of fine filaments and an affinity for silver and for periodic acid-Schiff stains.
Retzius' f.'s stiff f.'s in Deiters' cells.
rod f. a part of the rod cell of the retina that extends to either side of the cell body; the inner rod f. terminates in the spherule, a synaptic ending located in the outer plexiform layer.
Rosenthal f. an oval or elongated eosinophilic mass believed to represent a modified process of an astrocyte; seen in large numbers in certain slowly growing astrocytomas and areas of chronic reactive gliosis.
Sappey's f.'s nonstriated muscular f.'s in the check ligaments of the eyeball.
Sharpey's f.'s perforating f.'s
skeletal muscle f.'s multinucleated contractile cells varying from less than 10 to 100 mum in diameter and from less than 1 mm to several centimeters in length; the f. consists of sarcoplasm and cross-striated myofibrils, which in turn consist of myofilaments; human skeletal muscles are a mixture of red, white, and intermediate type f.'s.
spindle f. See mitotic spindle.
spinoreticular f.'s nerve f.'s originating from the spinal cord and terminating in the reticular formation of the brainstem.spinoreticular tract;
stress f.'s long bundles of microfilaments made up of actin; believed to be involved in the attachment of cultured cells to a substratum and also in the determination of the shape of cells such as fibroblasts; may be involved in cellular mobility.
striatonigral f.'s strionigral f.'s
strionigral f.'s nerve f.'s originating from cells of the caudate and putamen and terminating mainly in the pars reticulata of the substantia nigra; they utilize GABA and substance P.striatonigral f.'s;
sudomotor f.'s postganglionic and cholinergic sympathetic nerve f.'s that innervate the sweat glands.
sustentacular f.'s of retina Müller's f.'s (2)
T f. a f. that branches at right angles to the right and left; term used to describe the branching patterns of granular cell axons in the molecular layer of the cerebellum.
tautomeric f.´s nerve f.'s of the spinal cord that do not extend beyond the limits of the spinal cord segment in which they originate.
thalamocortical f.'s a general term identifying nerve f.'s arising from nuclei of the thalamus and projecting to, and terminating in, the cerebral cortex.
Tomes' f.'s dentinal f.'s (1)
transseptal f.'s nonelastic f.'s running from tooth to tooth over the crest of the alveolus.
transverse pontine f.'s f.'s arising from the pontine nuclei, decussate and pass into the cerebellum as the middle cerebellar peduncles.fibrae pontis transversae [NA] ;
unmyelinated f.'s a f. having no myelin covering (CNS); a naked axon; in the PNS represented by all axons lying in troughs in a single Schwann cell (Schwann cell unit); a slow conducting f.gray f.'s, nonmedullated f.'s, Remak's f.'s;
vasomotor f.'s postganglionic visceral efferent f.'s innervating the smooth muscles of vessel walls.
Weitbrecht's f.'s retinaculum of articular capsule of hip
white f. 1. white mammalian muscle f.'s; larger in diameter than red f.'s they have less myoglobin, sarcoplasm, and mitochondria, and contract more quickly; 2. collagen f
yellow f.'s elastic f.'s
zonular f.'s delicate fibers that pass from the equator of the lens to the ciliary body, collectively known as the ciliary zonule.fibrae zonulares [NA] ;


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