tract

tract (trakt)

An elongated area, e.g., path, track, way. See also fascicle.tractus; [L. tractus, a drawing out]
alimentary t. digestive t
anterior corticospinal t. anterior pyramidal t
anterior pyramidal t. uncrossed fibers forming a small bundle in the pyramidal t. See pyramidal t.tractus corticospinalis anterior [NA], tractus pyramidalis anterior [NA], anterior corticospinal t., anterior pyramidal fasciculus, direct pyramidal t., fasciculus corticospinalis anterior, fasciculus pyramidalis anterior, Türck's bundle, Türck's column, Türck's t;
anterior spinocerebellar t. a bundle of fibers originating in the base of the posterior horn and zona intermedia throughout lumbosacral segments of the spinal cord, crossing to the opposite side and ascending in a peripheral position in the ventral half of the lateral funiculus. In its ascent through the rhombencephalon, the tract curves sharply dorsalward along the rostral border of the trigeminal motor nucleus, entering the cerebellum in a caudal direction over the dorsal surface of the superior cerebellar peduncle, and terminating as mossy fibers in the granular layer of the cortex of the cerebellar vermis. The bundle conveys proprioceptive and exteroceptive information largely from the opposite lower extremity.tractus spinocerebellaris anterior [NA], Gowers' column, Gowers' t., ventral spinocerebellar t;
anterior spinothalamic t. the more anterior or ventral part of the spinothalamic t. that is involved in tactile sensation. See spinothalamic t.tractus spinothalamicus anterior [NA], ventral spinothalamic t;
Arnold's t. temporopontine t
association t. See association system.
auditory t. lateral lemniscus
Burdach's t. cuneate fasciculus
central tegmental t. a large fiber bundle passing longitudinally through the central mesencephalic and pontine tegmentum, distinguished from adjacent longitudinal groups of fiber-fascicles of the reticular formation by a more compact composition. In transverse sections of the mesencephalon the bundle occupies a large triangular area lateral to the medial longitudinal fasciculus; farther caudally it expands ventralward and finally passes over the lateral side of the (inferior) olivary nucleus, becoming part of the latter's fiber capsule. The bundle contains fibers from the mesencephalic tegmentum and regions surrounding the central gray substance descending to the olivary nucleus; it also includes numerous fibers ascending from the medullary, pontine, and mesencephalic reticular formation to the thalamus and subthalamus region.tractus tegmentalis centralis [NA], central tegmental fasciculus, tractus centralis tegmenti;
cerebellorubral t. that component of the superior cerebellar peduncle (brachium conjunctivum) which distributes fibers within the red nucleus of the opposite side.tractus cerebellorubralis [NA];
cerebellothalamic t. that component of the superior cerebellar peduncle (brachium conjunctivum) which originates in the cerebellar nuclei, crosses completely in the decussation of the brachia conjunctiva, bypasses the red nucleus, and terminates in parts of the ventral anterior, ventral intermediate, ventral posterolateral, and central lateral nuclei of the thalamus.tractus cerebellothalamicus [NA], dentatothalamic t;
Collier's t. medial longitudinal fasciculus
comma t. of Schultze semilunar fasciculus
corticobulbar t. collective term for those fibers (corticonuclear fibers) which separate from the corticospinal tract in the course of the latter's descent through the pons and medulla oblongata. Fibers of this t. innervate the motor nuclei of the trigeminal, facial, and hypoglossal nerves (perhaps also the nucleus ambiguus), directly and by way of interneurons in the lateral part of the rhombencephalic tegmentum. No direct supranuclear cortical innervation of the motor nuclei innervating the external eye muscles (oculomotor, trochlear, abducens) has been identified. Fibers of the corticobulbar t. also project into the formatio reticularis (i.e., corticoreticular fibers) and terminate upon sensory relay nuclei (e.g., gracile and cuneate nuclei, nucleus spinalis trigeminalis and nucleus solitarius).tractus corticobulbaris;
corticopontine t. collective term for the multitude of fibers which, originating in all of the major subdivisions of the cerebral cortex, descend in the internal capsule and crus cerebri to terminate in the nuclei of the ventral part of the pons. Individual components of this massive fiber system are indicated, according to their origin in the cerebral cortex, as the frontopontine t., parietopontine t., occipitopontine t., and temporopontine t.tractus corticopontini [NA];
corticospinal t. pyramidal t
crossed pyramidal t. lateral pyramidal t
cuneocerebellar t. the nerve fiber system originating from the accessory cuneate nucleus and entering the cerebellum as a component of the restiform body, the larger part of the inferior cerebellar peduncle.
dead t.'s dentin areas characterized by degenerated odontoblastic processes; may result from injury caused by caries, attrition, erosion, or cavity preparation.
deiterospinal t. vestibulospinal t
dentatothalamic t. cerebellothalamic t
descending t. of trigeminal nerve spinal t. of trigeminal nerve
digestive t. the passage leading from the mouth to the anus through the pharynx, esophagus, stomach, and intestine.alimentary canal, alimentary t., digestive tube, tubus digestorius;
direct pyramidal t. anterior pyramidal t
dorsolateral t. dorsolateral fasciculus
fastigiobulbar t. a fiber bundle originating in the fastigial nucleus (nucleus tecti) of both sides, passing out of the cerebellum in the inferior cerebellar peduncle (corpus restiforme), and distributing its fibers to the vestibular nuclei and other cell groups in the medulla oblongata. Prominent crossed fibers loop over the dorsal surface of the superior cerebellar peduncle before turning ventrally, forming the uncinate bundle of Russell.tractus fastigiobulbaris;
Flechsig's t. posterior spinocerebellar t
frontopontine t. a large group of fibers arising from the frontal lobe of the cerebral hemisphere, especially the precentral gyrus, descending in the capsula interna, farther caudally composing the medial part of the crus cerebri in which they extend caudalward to end in the gray matter (pontine nuclei) of the ventral part of the pons.tractus frontopontinus [NA];
frontotemporal t. unciform fasciculus
gastrointestinal t. (G.I. t.) the stomach, small intestine, and large intestine; often used as a synonym of digestive t.
geniculocalcarine t. optic radiation
genital t. the genital passages of the urogenital apparatus.genital duct;
t. of Goll fasciculus gracilis
Gowers' t. anterior spinocerebellar t
habenulointerpeduncular t. retroflex fasciculus
habenulopeduncular t. tractus habenulopeduncularis;
Hoche's t. See semilunar fasciculus.
hypothalamohypophysial t. supraopticohypophysial t
iliopubic t. thickened inferior margin of the transversalis fascia seen as a fibrous band running parallel and posterior (deep) to the inguinal ligament, contributing to the posterior wall of the inguinal canal as it bridges the external iliac-femoral vessels from the iliopectineal arch to the superior pubic ramus. It marks the inferior edge of the deep inguinal ring and the medial margin of the femoral canal. Seen only when the inguinal region is viewed from its internal aspect, it is a useful landmark in laparoscopy of this region, as for repair of inguinal herniae.deep crural arch, Thompson's ligament;
iliotibial t. a fibrous reinforcement of the fascia lata on the lateral surface of the thigh, extending from the crest of the ilium to the lateral condyle of the tibia.tractus iliotibialis [NA], iliotibial band, Maissiat's band;
James t.'s James fibers, under fiber
lateral corticospinal t. lateral pyramidal t
lateral pyramidal t. those fibers of the pyramidal t. that cross to the opposite side in the pyramidal decussation and descend in the dorsal half of the lateral funiculus of the spinal cord; they are distributed throughout the length of the spinal cord to interneurons of the zona intermedia of the spinal gray matter. See pyramidal t.tractus corticospinalis lateralis [NA], tractus pyramidalis lateralis [NA], crossed pyramidal t., fasciculus corticospinalis lateralis, fasciculus pyramidalis lateralis, lateral corticospinal t., lateral pyramidal fasciculus;
lateral spinothalamic t. the dorsal part of the spinothalamic t., which conveys impulses associated with pain and temperature sensation. See spinothalamic t.tractus spinothalamicus lateralis [NA];
Lissauer's t. dorsolateral fasciculus
Loewenthal's t. tectospinal t
mamillothalamic t. mamillothalamic fasciculus
Marchi's t. tectospinal t
mesencephalic t. of trigeminal nerve located alongside the central substance of the midbrain and composed of primary sensory fibers, the cells of origin of which compose the mesencephalic nucleus of the trigeminus.tractus mesencephalicus nervi trigemini [NA];
Monakow's t. rubrospinal t
t. of Münzer and Wiener tectopontine t
nerve t. a bundle or group of nerve fibers in the brain or spinal cord.
occipitocollicular t. occipitotectal t
occipitopontine t. a group of fibers originating in the occipital lobe of the cerebral hemisphere and descending in the internal capsule and lateral part of the crus cerebri to the pontine nuclei or ventral part of the pons.tractus occipitopontinus [NA];
occipitotectal t. the system of nerve fibers by which the occipital cortex projects to the superior colliculus.occipitocollicular t;
olfactory t. a nervelike, white band composed primarily of nerve fibers originating from the mitral cells and tufted cells of the olfactory bulb but also containing the scattered cells of the anterior olfactory nucleus. The t. is closely applied to the ventral surface of the frontal lobe, and attaches itself to the base of the cerebral hemisphere at the olfactory trigone, beyond which it extends in the form of the olfactory striae which distribute their fibers to the olfactory tubercle and, in largest number, to the olfactory cortex on and around the uncus of the parahippocampal gyrus. See also olfactory nerves, under nerve.tractus olfactorius [NA], olfactory peduncle;
olivocerebellar t. a large group of loosely arranged fiber fascicles emerging from the hilus of the olivary nucleus, crossing to the opposite side of the medulla oblongata through the stratum interolivare lemnisci and the contralateral olive, and joining the restiform body, the larger part of the contralateral inferior cerebellar peduncle; its fibers terminate in all parts of the cerebellar cortex as climbing fibers.tractus olivocerebellaris [NA];
olivocochlear t. See olivocochlear bundle.
olivospinal t. a slender bundle of nerve fibers in the peripheral zone of the lateral funiculus of the spinal cord, composed of spino-olivary fibers more likely than olivospinal fibers.Helweg's bundle;
optic t. the continuation of the optic nerve fibers beyond (behind) the latter's hemidecussation in the optic chiasm; each of the two symmetrical optic t.'s is composed of fibers originating from the temporal half of the retina of the ipsilateral eye and a nearly equal number of fibers from the nasal half of the contralateral retina; it forms a compact, somewhat flattened fiber band passing caudolaterally alongside the base of the hypothalamus and over the basal surface of the crus cerebri; most of its fibers terminate in the lateral geniculate body; a smaller number of fibers enter the brachium of the superior colliculus, to terminate in the superior colliculus and the pretectal region.tractus opticus [NA];
parietopontine t. a system of fibers originating in the parietal lobe of the cerebral hemisphere which descend in the internal capsule and lateral part of the crus cerebri to terminate in the pontine nuclei or ventral part of the pons.tractus parietopontinus [NA];
posterior spinocerebellar t. a compact bundle of heavily myelinated, thick fibers at the periphery of the dorsal half of the lateral funiculus of the spinal cord, originating in the ipsilateral thoracic nucleus (column of Clarke) and ascending by way of the inferior cerebellar peduncle. Terminals end as mossy fibers in the granular layer of the cortex of the cerebellar vermis. The bundle conveys largely proprioceptive information originating from the annulospiral nerve endings surrounding muscle spindles and from Golgi tendon organs.tractus spinocerebellaris posterior [NA], Flechsig's t;
prepyramidal t. rubrospinal t
pyramidal t. a massive bundle of fibers originating from pyramidal cells of various sizes in the fifth layer of the precentral motor (area 4), the premotor area (area 6), and to a lesser extent from the postcentral gyrus. Cells of origin in area 4 include the gigantopyramidal cells of Betz. Fibers from these cortical regions descend through the internal capsule, the middle third of the crus cerebri, and the ventral part of the pons to emerge on the ventral surface of the medulla oblongata as the pyramis. Continuing caudally, most of the fibers cross to the opposite side in the pyramidal decussation and descend in the dorsal half of the lateral funiculus of the spinal cord as the lateral pyramidal t., which distributes its fibers throughout the length of the spinal cord to interneurons of the zona intermedia of the spinal gray matter. In the (extremity-related) spinal cord enlargements, fibers also pass directly to motoneuronal groups that innervate distal extremity muscles subserving particular hand-and-finger or foot-and-toe movements. The uncrossed fibers form a small bundle, the anterior pyramidal t., which descends in the anterior funiculus of the spinal cord and terminates in synaptic contact with interneurons in the medial half of the anterior horn on both sides of the spinal cord. Interruption of the pyramidal tract at or below its cortical origin causes impairment of movement in the opposite body-half, especially severe in the arm and leg; characterized by muscular weakness, spasticity and hyperreflexia, and a loss of discrete finger and hand movements. Babinski's sign is associated with this condition of hemiplegia.tractus corticospinalis [NA], tractus pyramidalis [NA], corticospinal t;
respiratory t. the air passages from the nose to the pulmonary alveoli, through the pharynx, larynx, trachea, and bronchi.
reticulospinal t. collective term denoting a variety of fiber tracts descending to the spinal cord from the reticular formation of the pons and medulla oblongata. Part of these fibers conduct impulses from the neural mechanisms regulating autonomic functions to the corresponding somatic and visceral motor neurons of the spinal cord; others form links in nonpyramidal motor mechanisms affecting muscle tonus, reflex activity, and somatic movement.tractus reticulospinalis [NA];
rubrobulbar t. 1. that component of the rubrospinal t. which distributes its fibers to lateral parts of the rhombencephalic tegmentum rather than the spinal cord; 2. uncrossed rubro-olivary fibers.
rubroreticular t. fibers that pass from the red nucleus to the reticular formation of the pons and medulla.
rubrospinal t. a somatotopically organized fiber bundle, relatively small in humans, arising from the red nucleus, immediately crossing in the ventral tegmental decussation, descending near the lateral surface of the brainstem into the lateral funiculus of the spinal cord at the ventral border of the lateral pyramidal t. It terminates in the zona intermedia of the spinal cord where its distribution coincides with that of the lateral pyramidal t.; in contrast to the latter it appears not to have direct connections with spinal motor neurons. Impulses conveyed by this t. indirectly increase flexor muscle tone.tractus rubrospinalis [NA], Monakow's bundle, Monakow's t., prepyramidal t;
t. of Schütz dorsal longitudinal fasciculus
sensory t. See lemniscus.
septomarginal t. See semilunar fasciculus.
solitary t. a slender, compact fiber bundle extending longitudinally through the dorsolateral region of the medullary tegmentum, surrounded by the nucleus of the solitary t., below the obex decussating over the central canal, and descending over some distance into the upper cervical segments of the spinal cord. It is composed of primary sensory fibers that enter with the vagus, glossopharyngeal, and facial nerves, and in part convey information from stretch receptors and chemoreceptors in the walls of the cardiovascular, respiratory, and intestinal tracts; in rostral parts of the tract impulses are generated by the receptor cells of the taste buds in the mucosa of the tongue. Its fibers are distributed to the nucleus of the solitary tract.tractus solitarius [NA], fasciculus rotundus, fasciculus solitarius, funiculus solitarius, Gierke's respiratory bundle, Krause's respiratory bundle, round fasciculus, solitary bundle, solitary fasciculus;
sphincteroid t. of ileum basal sphincter
spinal t. any one of a multitude of fiber bundles ascending or descending in the spinal cord.
spinal t. of trigeminal nerve a compact fiber bundle, comma-shaped on transverse section, composed of primary sensory fibers of the portio major of the trigeminal nerve, descending from the level of the entrance of the trigeminus in the upper pons down through the dorsolateral region of the rhombencephalic tegmentum along the lateral side of the descending or spinal nucleus of the trigeminus, emerging on the dorsolateral surface of the lower medulla oblongata as the tuberculum cinereum, and continuing as far as the second cervical segment of the spinal cord. Its fibers are distributed to the descending or spinal nucleus of the trigeminus.tractus spinalis nervi trigemini [NA], descending t. of trigeminal nerve, tractus descendens nervi trigemini;
spinocerebellar t.'s See anterior spinocerebellar t., posterior spinocerebellar t.
spinocervicothalamic t. a t. composed of axons that originate from laminae III-V, ascend ipsilaterally to the lateral cervical nucleus (LCN) where they synapse, LCN neurons project to the contralateral thalamus via the medial lemniscus.
spino-olivary t. multiple spinal tracts terminating in the accessory olivary nuclei. See olivospinal t.
spinoreticular t. spinoreticular fibers, under fiber
spinotectal t. the relatively small component of the spinothalamic t. that terminates in the intermediate and deep layers of the superior colliculus and in parts of the periaqueductal gray.tractus spinotectalis [NA];
spinothalamic t. a large ascending fiber bundle in the ventral half of the lateral funiculus of the spinal cord, arising from cells in the posterior horn at all levels of the cord, which cross within their segments of origin in the white commissure. In their contralateral ascent, the bundle is intermingled with numerous intersegmental fibers. The spinothalamic t. continues from the spinal cord into the brainstem, occupying a ventrolateral position and issuing numerous fibers to the rhombencephalic and mesencephalic reticular formation, to the lateral part of the central gray substance of the mesencephalon, and to the deep and intermediate layers of the superior colliculus; the relatively few fibers (10 to 20%) that remain form the true spinothalamic t. which enters the diencephalon and ends in the nucleus ventralis posterior (caudal part) and intralaminar nuclei of the thalamus. In its ascent in the spinal cord the t. is composed of a dorsal part, the lateral spinothalamic t., which conveys impulses associated with pain and temperature sensation, and a more ventral part, the anterior spinsothalamic t., involved in tactile sensation.lemniscus spinalis [NA], spinal lemniscus, tractus spinothalamicus;
spiral foraminous t. openings in the cochlear area of the bottom of the internal acoustic meatus through which the fibers of the cochlear nerve leave the bony labyrinth to enter the cranial cavity.tractus spiralis foraminosus [NA];
Spitzka's marginal t. dorsolateral fasciculus
sulcomarginal t. collective term for those fiber t.'s which descend in the anterior funiculus of the spinal cord along the wall of the anterior median fissure: tectospinal t., medial longitudinal fasciculus, and anterior pyramidal t.
supraopticohypophysial t. a bundle of unmyelinated fibers originating from all cells of the supraoptic nucleus and an estimated 20% of those of the paraventricular nucleus of the hypothalamus, which extend through the infundibulum and pituitary stalk to their endings in the posterior lobe of the hypophysis; the fibers convey neurosecretory substances, vasopressin and oxytocin, which are stored in (and can be released into the circulating blood from) their terminals. See also hypophysis, neurosecretion.tractus supraopticohypophysialis [NA], hypothalamohypophysial t;
tectobulbar t. fibers originating in the deep layers of the superior colliculus and accompanying the tectospinal t. but, unlike the latter, terminating in medial regions of the pontine and medullary tegmentum.tractus tectobulbaris;
tectopontine t. a fiber bundle arising in the superior colliculus, passing caudoventrally on the same side along the medial side of the lateral lemniscus, issuing fibers terminating in the lateral zone of the mesencephalic tegmentum, and ending in the lateral part of the gray matter of the ventral part of the pons.t. of Münzer and Wiener, tractus tectopontinus;
tectospinal t. a bundle of thick, heavily myelinated fibers originating in the deep layers of the superior colliculus, crossing to the opposite side in the dorsal tegmental decussation, descending along the median plane, between the medial longitudinal fasciculus dorsally, the medial lemniscus ventrally, into the anterior funiculus of the spinal cord. The t. ends in the medial region of the anterior horn of the cervical spinal cord, and appears to be involved in head movements during visual and auditory tracking. Throughout its course in the brainstem it is accompanied by fibers of the tectobulbar t.tractus tectospinalis [NA], Held's bundle, Loewenthal's bundle, Loewenthal's t., Marchi's t., predorsal bundle;
temporofrontal t. unciform fasciculus
temporopontine t. a fiber group originating in the cerebral cortex of the temporal lobe, particularly the superior and middle temporal gyri, following the sublenticular limb of the internal capsule into the lateral margin of the crus cerebri in which it descends to its termination in the pontine nuclei or the ventral part of the pons.tractus temporopontinus [NA], Arnold's bundle, Arnold's t;
trigeminothalamic t. general term designating projections from the spinal trigeminal and principal sensory nuclei of the trigeminal nerve to the thalamus; divided into a ventral trigeminothalamic t. (spinal trigeminal nucleus projections to the contralateral ventral posteromedial nucleus-VPM) and a dorsal trigeminothalamic t. (principal sensory nucleus projections to the ipsilateral VPM); See also trigeminal lemniscus.
tuberoinfundibular t. a system of fine, unmyelinated fibers apparently originating from small-celled nuclei of the tuber cinereum, especially the arcuate nucleus, and terminating in the median eminence of the infundibulum, in contact with modified ependymal cells and the capillary tufts from which the hypothalamohypophysial portal veins originate. See also hypophysis, neurosecretion.tractus tuberoinfundibularis;
Türck's t. anterior pyramidal t
urinary t. the passage from the pelvis of the kidney to the urinary meatus through the ureters, bladder, and urethra.
uveal t. vascular tunic of eye
ventral spinocerebellar t. anterior spinocerebellar t
ventral spinothalamic t. anterior spinothalamic t
vestibulospinal t. a somatopically organized fiber bundle originating from the lateral vestibular nucleus (nucleus of Deiters) which descends uncrossed into the anterior funiculus of the spinal cord lateral to the anterior median fissure; the t. extends throughout the length of the cord, distributing fibers at all levels to the medial part of the anterior horn. Excitatory impulses conveyed by the vestibulospinal t. increase extensor muscle tone.tractus vestibulospinalis [NA], deiterospinal t;
Waldeyer's t. dorsolateral fasciculus

 

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