An elongated area, e.g., path, track, way. SEE ALSO: fascicle. SYN: tractus. [L. tractus, a drawing out]
- alimentary t. SYN: digestive t..
- anterior corticospinal t. uncrossed fibers forming a small bundle in the anterior funiculus of the spinal cord. See pyramidal t.. SEE ALSO: corticospinal t.. SYN: tractus corticospinalis anterior [TA], anterior pyramidal fasciculus, anterior pyramidal t., direct pyramidal t., fasciculus corticospinalis anterior, fasciculus pyramidalis anterior, tractus pyramidalis anterior, Türck bundle, Türck column, Türck t..
- anterior raphespinal t. [TA] a group of axons that originate in the raphe nuclei, primarily of the medulla oblongata and caudal pons, and descend in the anterior funiculus. SYN: tractus raphespinalis anterior [TA], ventral raphespinal t. [TA].
- anterior spinocerebellar t. [TA] 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 t. 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, although some of its fibers recross in the cerebellum. SYN: tractus spinocerebellaris anterior [TA], ventral spinocerebellar t., Gowers column, Gowers t..
- anterior spinothalamic t. [TA] the more anterior or ventral part of the composite bundle, the anterolateral system, formed by the anterior and lateral spinothalamic tracts. These specific fibers are involved in tactile sensation. See spinothalamic t.. SEE ALSO: anterolateral system. SYN: tractus spinothalamicus anterior [TA], ventral spinothalamic t..
- anterior trigeminothalamic t. [TA] fibers that originate from the spinal trigeminal nucleus, cross the midline, and ascend on the contralateral side to terminate in the ventral posteromedial nucleus (VPM). This t. also contains, in the rostral pons and in the midbrain, fibers that originate in the contralateral principal sensory nucleus and that also terminate in the VPM. SYN: tractus trigeminothalamicus anterior [TA], ventral trigeminothalamic t. [TA].
- anterolateral t. SYN: anterolateral system.
- Arnold t. SYN: temporopontine t..
- association t. association system.
- bulboreticulospinal t. [TA] a t. that originates from the gigantocellular reticular nucleus of the medulla, descends primarily as an uncrossed t., and terminates mainly in spinal laminae VII and VIII. SYN: lateral reticulospinal t. [TA], medullary reticulospinal t. [TA], tractus bulboreticulospinalis [TA].
- caerulospinal t. [TA] a collection of axons that originate from the nucleus caeruleus and subcaeruleus area and project bilaterally to the gray matter of the spinal cord to all spinal levels; they are a major source of noradrenergic input to the spinal cord. SYN: tractus caeruleospinalis [TA].
- central tegmental t. [TA] 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. SYN: tractus tegmentalis centralis [TA], central tegmental fasciculus.
- cerebellorubral t. that component of the superior cerebellar peduncle (brachium conjunctivum) which distributes fibers within the red nucleus of the opposite side. SYN: tractus cerebellorubralis.
- 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. SYN: dentatothalamic t., tractus cerebellothalamicus.
- corticobulbar t. See corticonuclear fibers, under fiber. SYN: 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 basilar part of the pons. Individual components of this massive fiber system are indicated, according to their origin in the cerebral cortex, as the frontopontine fibers [TA], parietopontine fibers [TA], occipitopontine fibers [TA], and temporopontine fibers [TA]. SYN: tractus corticopontinus [TA].
- corticospinal t. a composite bundle of corticospinal fibers [TA] that descend into and through the medulla to form the lateral corticospinal t. [TA] and the anterior corticospinal t. [TA]. This massive bundle of fibers originates 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 pyramid. 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 corticospinal 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 corticospinal 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 corticospinal fibers 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 sign is associated with this condition of hemiplegia. SYN: pyramidal t. [TA], tractus pyramidalis [TA], tractus corticospinalis.
- 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. SYN: cuneocerebellar fibers [TA], fibrae cuneocerebellares [TA].
- dead tracts dentin areas characterized by degenerated odontoblastic processes; may result from injury caused by caries, attrition, erosion, or cavity preparation.
- deiterospinal t. SYN: lateral vestibulospinal t..
- dentatothalamic t. SYN: cerebellothalamic t..
- digestive t. the passage leading from the mouth to the anus through the pharynx, esophagus, stomach, and intestine. SYN: alimentary canal, alimentary t., digestive tube, tubus digestorius.
- 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 medial portion of the inferior cerebellar peduncle (corpus juxtarestiforme), 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. SYN: tractus fastigiobulbaris.
- fastigiospinal t. [TA] See fastigiospinal fibers, under fiber. SYN: tractus fastigiospinalis [TA].
- frontopontine t. [TA] See frontopontine fibers, under fiber. SYN: tractus frontopontinus.
- frontotemporal t. SYN: unciform fasciculus.
- gastrointestinal t. (G.I. t.) the stomach, small intestine, and large intestine; often used as a synonym of digestive t..
- geniculocalcarine t. SYN: optic radiation.
- t. of Goll SYN: gracile fasciculus.
- habenulointerpeduncular t., habenulopeduncular t. [TA] SYN: retroflex fasciculus.
- hypothalamohypophysial t. [TA] SYN: supraopticohypophysial t..
- iliopubic t. [TA] 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. SYN: tractus iliopubicus [TA], deep crural arch, Thompson ligament.
- iliotibial t. [TA] a fibrous reinforcement of the fascia lata on the lateral surface of the thigh, extending from the crest of the ilium (especially the tuberculum of the crest) to the anterolateral aspect of the lateral condyle of the tibia (Gerdy tubercle). SYN: tractus iliotibialis [TA], iliotibial band, Maissiat band.
- interpositospinal t. [TA] a group of axons that originate in the anterior and posterior interposed cerebellar nuclei, primarily the latter, and descend to the spinal cord. SYN: tractus interpositospinalis [TA].
- interstitiospinal t. [TA] a group of axons that originate in the interstitial nucleus of the midbrain, descend ipsilaterally, and terminate primarily in spinal laminae VII, VIII of Rexed. SYN: tractus interstitiospinalis [TA].
- lateral corticospinal t. [TA] those fibers that cross to the opposite side in the corticospinal (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, to some of the nuclei of the posterior horn, and to interneuron pools of the anterior horn. SEE ALSO: corticospinal t.. SYN: tractus corticospinalis lateralis [TA], crossed pyramidal t., fasciculus corticospinalis lateralis, fasciculus pyramidalis lateralis, lateral pyramidal fasciculus, lateral pyramidal t., tractus pyramidalis lateralis.
- lateral raphespinal t. [TA] a group of axons that arise in the nucleus raphe magnus, descend in the posterior portion of the lateral funiculus, and terminate primarily in the posterior (dorsal) horn. These serotoninergic fibers are involved in the inhibition of transmission of nociceptive information through the dorsal horn. SYN: tractus raphespinalis lateralis [TA].
- lateral reticulospinal t. [TA] SYN: bulboreticulospinal t..
- lateral spinothalamic t. [TA] the more dorsal or dorsolateral part of the composite bundle, the anterolateral system, formed by the lateral and anterior spinothalamic tracts; these specific fibers convey impulses associated with pain and temperature sensation. See spinothalamic t.. SYN: tractus spinothalamicus lateralis [TA].
- lateral 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 tractus 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. SYN: tractus vestibulospinalis lateralis [TA], deiterospinal t., tractus vestibulospinalis.
- Lissauer t. SYN: dorsolateral fasciculus.
- Loewenthal t. SYN: tectospinal t..
- mamillothalamic t. SYN: mammillothalamic fasciculus.
- Marchi t. SYN: tectospinal t..
- medial reticulospinal t. [TA] SYN: pontoreticulospinal t..
- medial vestibulospinal t. [TA] fibers that originate from the medial vestibular nucleus and descend in the spinal cord as a component of the medial longitudinal fasciculus. SYN: tractus vestibulospinalis medialis [TA], tractus vestibulospinalis medialis [TA].
- medullary reticulospinal t. [TA] SYN: bulboreticulospinal t..
- mesencephalic t. of trigeminal nerve [TA] 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. SYN: tractus mesencephalicus nervi trigemini [TA].
- Monakow t. SYN: rubrospinal t..
- t. of Münzer and Wiener SYN: tectopontine t..
- occipitocollicular t. SYN: occipitotectal t..
- occipitopontine t. See occipitopontine fibers, under fiber. SYN: tractus occipitopontinus.
- occipitotectal t. See occipitotectal fibers, under fiber. SYN: occipitocollicular t..
- olfactory t. [TA] 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 [CN I], under nerve. SYN: tractus olfactorius [TA], olfactory peduncle.
- olivocerebellar t. [TA] 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 and in the cerebellar nuclei; all olivocerebellar projections are crossed. SYN: tractus olivocerebellaris [TA].
- olivocochlear t. [TA] fibers that originate from the periolivary nuclei bilaterally, exit the brianstem on the vestibular nerve, join the cochlear nerve in the inner ear, and terminate on outer hair cells. SYN: tractus olivocochlearis [TA], bundle of Rasmussen.
- olivospinal t. See olivospinal fibers, under fiber. SYN: Helweg bundle.
- optic t. [TA] the continuation of the optic nerve fibers beyond (behind) the latter's hemidecussation in the optic chiasm; each of the two symmetric optic tracts 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. SYN: tractus opticus.
- parietopontine t. See parietopontine fibers, under fiber. SYN: tractus parietopontinus.
- pontoreticulospinal t. [TA] a t. that originates from oral and caudal pontine reticular nuclei, descends bilaterally but with an ipsilateral preponderance, and terminates mainly in spinal laminae VII and VIII. SYN: medial reticulospinal t. [TA], tractus pontoreticulospinalis [TA].
- posterior spinocerebellar t. [TA] 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 and, via collaterals, in the cerebellar nuclei. The bundle conveys largely proprioceptive information originating from the annulospiral nerve endings surrounding muscle spindles and from Golgi tendon organs. SYN: tractus spinocerebellaris posterior [TA], dorsal spinocerebellar t., Flechsig t..
- posterior trigeminothalamic t. [TA] fibers that originate primarily in dorsomedial portion of the principal sensory nucleus and ascend on the ipsilateral side to terminate in the ventral posteromedial nucleus. SYN: dorsal trigeminothalamic t. [TA], tractus trigeminothalamicus posterior [TA].
- posterolateral t. [TA] SYN: dorsolateral fasciculus.
- prepyramidal t. SYN: rubrospinal t..
- pyramidal t. [TA] SYN: 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. SEE ALSO: bulboreticulospinal t., pontoreticulospinal t.. SYN: tractus reticulospinalis.
- rubrobulbar t. [TA] 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. SYN: tractus rubrobulbaris [TA], tractus rubrobulbaris.
- rubropontine t. [TA] axons arising in cells of the red nucleus of the midbrain and terminating in the pontine nuclei of the basilar pons. SYN: tractus rubropontinus [TA].
- rubroreticular t. fibers that pass from the red nucleus to the reticular formation of the pons and medulla.
- rubrospinal t. [TA] 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. SYN: tractus rubrospinalis [TA], Monakow bundle, Monakow t., prepyramidal t..
- t. of Schütz SYN: dorsal longitudinal fasciculus.
- septomarginal t. semilunar fasciculus.
- solitariospinal t. [TA] a group of axons that arise in the solitary nucleus and descend bilaterally, mainly in dorsal regions of the lateral funiculus. SYN: tractus solitariospinalis [TA].
- solitary t. [TA] 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 t. 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 t.. SYN: tractus solitarius [TA], fasciculus rotundus, fasciculus solitarius, funiculus solitarius, Gierke respiratory bundle, Krause respiratory bundle, round fasciculus, solitary bundle, solitary fasciculus.
- spinal t. of trigeminal nerve [TA] 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. SYN: tractus spinalis nervi trigemini [TA], descending t. of trigeminal nerve, tractus descendens nervi trigemini.
- spinocervical t. [TA] a t. composed of axons that originate from laminae III-V and ascend ipsilaterally to the lateral cervical nucleus (LCN) where they synapse, LCN neurons project to the contralateral thalamus via the medial lemniscus. SYN: tractus spinocervicalis [TA], spinocervicothalamic t., tractus spinocervicalis.
- spinocervicothalamic t. SYN: spinocervical t..
- spinoolivary t. [TA] multiple spinal tracts terminating in the dorsal and medial accessory olivary nuclei. SEE ALSO: olivospinal t.. SYN: tractus spinoolivaris [NA].
- spinoolivary t. [TA] a collection of axons, actually comprising several bundles, that originate from the spinal gray, ascend ipsilaterally to terminate in the accessory olivary nuclei. SYN: tractus spinoolivaris [TA].
- spinoreticular t. [TA] SYN: spinoreticular fibers, under fiber.
- spinotectal t. [TA] the relatively small component of the anterolateral system that terminates in the intermediate and deep layers of the superior colliculus; part of a larger population of spinomesencephalic fibers that also includes spinal projections to the periaqueductal gray substance (spinoperiaqueductal fibers). SYN: tractus spinotectalis [TA].
- spinothalamic t. a general term describing 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. This t., part of a larger bundle commonly called the spinal lemniscus or anterolateral t. (anterolateral system), contains spinothalamic fibers, spinoreticular fibers, spinohypothalamic fibers, spinomesencephalic fibers (as spinotectal and spinoperiaqueductal fibers), and some projections from the spinal cord to the inferior olivary complex (spinoolivary). In their contralateral ascent, the bundle is intermingled with numerous intersegmental fibers. These fibers continue from the spinal cord into the brainstem, occupying a ventrolateral position and issuing numerous fibers to the rhombencephalic and mesencephalic reticular formation (spinoreticular fibers) to the accessory olivary nuclei (spinoolivary) fibers, to the lateral part of the central gray substance of the mesencephalon (spinoperiaqueductal fibers), and to the deep and intermediate layers of the superior colliculus (spinotectal fibers); the relatively few fibers (10–20%) that remain are the spinothalamic fibers which enter the diencephalon and ends in the nucleus ventralis posterior (caudal part) and intralaminar nuclei of the thalamus. In its ascent in the spinal cord this t. was originally described as being 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. It is now known that this division is not as obvious as originally thought. SYN: lemniscus spinalis [TA], spinal lemniscus [TA], tractus spinothalamicus.
- spinovestibular t. [TA] a group of axons that originate from neurons primarily in lumbosacral levels, ascend ipsilaterally and in close apposition to the posterior spinocerebellar t., and terminate in the lateral, medial and spinal vestibular nuclei. Some of these axons may be collaterals of posterior spinocerebellar fibers. SYN: tractus spinovestibularis [TA].
- spiral foraminous t. SYN: tractus spiralis foraminosus.
- sulcomarginal t. collective term for those fiber tracts 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. [TA] 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: pituitary gland, neurosecretion. SYN: hypothalamohypophysial t. [TA], tractus supraopticohypophysialis [TA].
- tectobulbar t. [TA] 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. SYN: tractus tectobulbaris [TA].
- tectopontine t. [TA] 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. SYN: tractus tectopontinus [TA], t. of Münzer and Wiener.
- tectospinal t. [TA] 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.. SYN: tractus tectospinalis [TA], Held bundle, Loewenthal bundle, Loewenthal t., Marchi t., predorsal bundle.
- temporofrontal t. SYN: unciform fasciculus.
- temporopontine t. See temporopontine fibers, under fiber. SYN: Arnold bundle, Arnold t., tractus temporopontinus.
- trigeminospinal t. [TA] axons that originate from neurons in the spinal nucleus of the trigeminal nerve and descend to the spinal cord primarily on the ipsilateral side. SYN: tractus trigeminospinalis [TA].
- trigeminothalamic t. general term designating projections from the spinal trigeminal and principal sensory nuclei of the trigeminal nerve to the thalamus. 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: pituitary gland, neurosecretion. SYN: tractus tuberoinfundibularis.
- Türck t. SYN: anterior corticospinal t..
- urinary t. the passage from the pelvis of the kidney to the urinary meatus through the ureters, bladder, and urethra.
- vocal t. the air passages above the glottis (including the pharynx, oral and nasal cavities, and the paranasal sinuses) that contribute to the quality of the voice.
- Waldeyer t. SYN: dorsolateral fasciculus.
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tract 'trakt n
1) a system of body parts or organs that act together to perform some function <the digestive \tract> see GASTROINTESTINAL TRACT, LOWER RESPIRATORY TRACT, UPPER RESPIRATORY TRACT
2) a bundle of nerve fibers having a common origin, termination, and function and esp. one within the spinal cord or brain called also fiber tract see CORTICOSPINAL TRACT, OLFACTORY TRACT, OPTIC TRACT, SPINOTHALAMIC TRACT compare FASCICULUS (b)
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n.
1. a group of nerve fibres passing from one part of the brain or spinal cord to another, forming a distinct pathway, e.g. the spinothalamic tract, pyramidal tract, and corticospinal tract.
2. an organ or collection of organs providing for the passage of something, e.g. the digestive tract.
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(trakt) [L. tractus] 1. a region, principally one of some length. 2. a collection or bundle of nerve fibers having the same origin, function, and termination (tractus [TA]); see also under bundle, fasciculus, and lemniscus. 3. a number of organs, arranged in series, subserving a common function.For descriptions of specific anatomic structures not listed here, see under tractus, and see under the entries listed above.
Medical dictionary. 2011.