| tractus habenulopeduncularis | tractus habenulopeduncularis |
|---|---|
| tractus iliotibialis | 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. Synonym: tractus iliotibialis, iliotibial band, Maissiat's band. (05 Mar 2000) |
| tractus occipitopontinus | A group of fibres 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. Synonym: tractus occipitopontinus. (05 Mar 2000) |
| tractus olfactorius | A nervelike, white band composed primarily of nerve fibres originating from the mitral cells and tufted cells of the olfactory bulb but also containing the scattered cells of the anterior olfactory nucleus. The tract 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 fibres to the olfactory tubercle and, in largest number, to the olfactory cortex on and around the uncus of the parahippocampal gyrus. See: olfactory nerves. Synonym: tractus olfactorius, olfactory peduncle. (05 Mar 2000) |
| tractus olivocerebellaris | Synonym: olivocerebellar tract. (05 Mar 2000) |
| tractus opticus | The continuation of the optic nerve fibres beyond (behind) the latter's hemidecussation in the optic chiasm; each of the two symmetrical optic tracts is composed of fibres originating from the temporal half of the retina of the ipsilateral eye and a nearly equal number of fibres from the nasal half of the contralateral retina; it forms a compact, somewhat flattened fibre band passing caudolaterally alongside the base of the hypothalamus and over the basal surface of the crus cerebri; most of its fibres terminate in the lateral geniculate body; a smaller number of fibres enter the brachium of the superior colliculus, to terminate in the superior colliculus and the pretectal region. Synonym: tractus opticus. (05 Mar 2000) |
| tractus parietopontinus | A system of fibres 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. Synonym: tractus parietopontinus. (05 Mar 2000) |
| tractus pyramidalis | A massive bundle of fibres 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. Fibres 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 fibres 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 tract, which distributes its fibres 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, fibres also pass directly to motoneuronal groups that innervate distal extremity muscles subserving particular hand-and-finger or foot-and-toe movements. The uncrossed fibres form a small bundle, the anterior pyramidal tract, 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; characterised 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. Synonym: tractus corticospinalis, tractus pyramidalis, corticospinal tract. (05 Mar 2000) |
| tractus pyramidalis anterior | Uncrossed fibres forming a small bundle in the pyramidal tract. See: pyramidal tract. Synonym: tractus corticospinalis anterior, tractus pyramidalis anterior, anterior corticospinal tract, anterior pyramidal fasciculus, direct pyramidal tract, fasciculus corticospinalis anterior, fasciculus pyramidalis anterior, Turck's bundle, Turck's column, Turck's tract. (05 Mar 2000) |
| tractus pyramidalis lateralis | Those fibres of the pyramidal tract 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 tract. Synonym: tractus corticospinalis lateralis, tractus pyramidalis lateralis, crossed pyramidal tract, fasciculus corticospinalis lateralis, fasciculus pyramidalis lateralis, lateral corticospinal tract, lateral pyramidal fasciculus. (05 Mar 2000) |
| tractus reticulospinalis | Collective term denoting a variety of fibre tracts descending to the spinal cord from the reticular formation of the pons and medulla oblongata. Part of these fibres 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. Synonym: tractus reticulospinalis. (05 Mar 2000) |
| tractus rubrospinalis | A somatotopically organised fibre 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 tract. It terminates in the zona intermedia of the spinal cord where its distribution coincides with that of the lateral pyramidal tract; in contrast to the latter it appears not to have direct connections with spinal motor neurons. Impulses conveyed by this tract indirectly increase flexor muscle tone. Synonym: tractus rubrospinalis, Monakow's bundle, Monakow's tract, prepyramidal tract. (05 Mar 2000) |
| tractus solitarius | A slender, compact fibre bundle extending longitudinally through the dorsolateral region of the medullary tegmentum, surrounded by the nucleus of the solitary tract, 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 fibres 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 fibres are distributed to the nucleus of the solitary tract. Synonym: tractus solitarius, fasciculus rotundus, fasciculus solitarius, funiculus solitarius, Gierke's respiratory bundle, Krause's respiratory bundle, round fasciculus, solitary bundle, solitary fasciculus. (05 Mar 2000) |
| tractus spinocerebellaris anterior | A bundle of fibres 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 fibres in the granular layer of the cortex of the cerebellar vermis. The bundle conveys proprioceptive and exteroceptive information largely from the opposite lower extremity. Synonym: tractus spinocerebellaris anterior, Gowers' column, Gowers' tract, ventral spinocerebellar tract. (05 Mar 2000) |
| tractus spinocerebellaris posterior | A compact bundle of heavily myelinated, thick fibres 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 fibres 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. Synonym: tractus spinocerebellaris posterior, Flechsig's tract. (05 Mar 2000) |