(trakt )

[L. tractus, extent]

1. A pathway, course, or channel.
2. A bundle of parallel axons in the central nervous system (CNS) that runs along a stereotyped course from a common originating area to a common termination area.
3. A group of organs or parts that form a continuous pathway.

aerodigestive t.The anatomic region in the oral cavity and throat through which both air and food pass.

afferent t.Any axon tract that carries information toward a particular target area.

alimentary t.Digestive tract.

anterior spinocerebellar t.Ventral spinocerebellar tract.

ascending t.An axon tract running rostrally in the spinal cord or brain, often a sensory pathway.

biliary t.The organs and ducts through which bile travels on its way to the duodenum. These are the bile canaliculi, right and left hepatic ducts, common hepatic duct, gallbladder, cystic duct, bile duct, and hepatopancreatic ampulla.

SEE: bile ducts; gallbladder; liver.

TabersPlus.

Burdach t.

SEE: under Burdach, Karl.

central tegmental t.An axon tract connecting the subthalamus and the midbrain reticular formation with the inferior olivary nucleus.

corticobulbar t.An axon tract from the motor cortex that innervates the reticular formation and the cranial nerve nuclei in the hindbrain.

corticohypothalamic t.An axon tract from the frontal, parietal, and occipital cortices that innervates the hypothalamus.

corticospinal t.An axon tract from the motor cortex that travels into the spinal cord, synapsing at all levels. Axons of the corticospinal tract first converge into a bundle in the posterior limb of the internal capsule and continue as a compact bundle through the cerebral peduncle. In the pons, the corticospinal tract separates into several bundles that converge more caudally in the hindbrain as the pyramid. In the caudal hindbrain, the corticospinal tract crosses the midline in the pyramidal decussation and continues down the spinal cord as the lateral corticospinal tract.

cuneocerebellar t.An axon tract originating in the external cuneate nucleus and synapsing in the ipsilateral cerebellum.

descending t.Any axon tract running caudally in the spinal cord or brain, often a motor pathway.

digestive t.The continuous set of tubes that move food from the mouth to the anus. SYN: alimentary tract.

direct cerebellar t.Dorsal spinocerebellar tract.

dorsal spinocerebellar t.An ipsilateral (uncrossed) axonal tract originating throughout the posterior thoracic nucleus of the spinal cord. The tract runs in the lateral funiculus of the spinal cord and terminates in the ipsilateral vermis of the cerebellum. SYN: direct cerebellar tract; posterior spinocerebellar tract.

dorsolateral t.Lissauer tract.

efferent t.Any axon tract that carries information away from a particular target area.

extrapyramidal t.Any of the axon tracts of the extrapyramidal system.

SEE: extrapyramidal system.

frontopontine t.A tract that passes from the cerebral cortex of the frontal lobe through the internal capsule and cerebral peduncle to the pons.

gastrointestinal t.The esophagus, stomach, and intestines.

geniculocalcarine t.Optic radiation.

geniculohypothalamic t.An axon tract originating in the lateral geniculate nucleus of the thalamus and innervating the suprachiasmatic nuclei of the hypothalamus. The suprachiasmatic nuclei contain pacemakers of the circadian rhythm system, and the geniculohypothalamic tract provides visual input that helps to entrain the pacemaker cells.

genital t.1 In males, the channels by which spermatozoa leave the body.2In females, the channels in which the ovum grows and is fertilized and through which the baby leaves the body. SYN: reproductive tract.

genitourinary t.The genital and urinary tracts together. SYN: urogenital tract.

habenulo-interpeduncular t.Fasciculus retroflexus.

iliopubic t.Iinguinal ligament.

iliotibial t.A thickened band in the deep fascia along the lateral thigh (the fascia lata) that extends from the tubercle of the iliac crest to the lateral condyle of the tibia. The iliotibial tract is an aponeurosis shared by both the gluteus maximus and tensor fasciae latae muscles.

internodal t.In the heart, myocardial tissue in the right atrium that preferentially carries sinoatrial impulses to the left atrium, to the intra-atrial septum, or to the atrioventricular node.

intestinal t.The small and large intestines.

Lissauer t.

SEE: Lissauer tract.

lower gastrointestinal t.The anus, rectum, colon, cecum, ileum, and jejunum.

mammillotegmental t.An axon tract originating in the mammillary body and synapsing in small nuclei near the caudal end of the midbrain tegmentum.

mammillothalamic t.An axon tract originating in the mammillary body and synapsing in the anterior nucleus of the thalamus. The mammillothalamic tract is part of the limbic system. SYN: Vicq d'Azyr tract.

medullary reticulospinal t.

SEE: reticulospinal tract.

mesencephalic t. of the trigeminal nerve An axon tract of the unipolar sensory neurons of the trigeminal mesencephalic nucleus. Peripheral processes of these neurons run in the mesencephalic tract to the mand ibular nerve (CN V3) and carry proprioceptive information from the face and the teeth. Axons of these neurons run in the mesencephalic tract and innervate a number of central nuclei, including the trigeminal motor nucleus. SYN: trigeminal mesencephalic tract.

motor t.Any axon tract, usually running caudally in the CNS, that transmits efferent (output) information.

olfactory t.A white ribbon-like band along the bottom (orbital) surface of each frontal lobe, composed of axons from the mitral cells in olfactory bulb. These axons terminate in the piriform cortex (the primary olfactory cortex) at the base of the cerebral hemisphere.

olivocerebellar t.An axon tract running transversely (as opposed to longitudinally) in the hindbrain from the inferior olivary nucleus to all parts of the cerebellum via the inferior cerebellar peduncle.

optic t.The main bundle of axons from the optic nerves caudal to the optic chiasm. Axons from the temporal half of the retina continue in the ipsilateral optic tract; axons from the nasal half of the retina cross the midline of the brain in the optic chiasm and join the contralateral optic tract. Most optic tract axons synapse in the lateral geniculate nucleus of the thalamus; most of the remaining optic tract axons synapse in the superior colliculus (optic tectum) of the midbrain.

outflow t.That portion of either of the heart’s ventricles through which blood flows from the heart to either the aorta (the left ventricular outflow tract), or the pulmonary arteries (the right ventricular outflow tract).

pontine reticulospinal t.

SEE: reticulospinal tract.

posterior spinocerebellar t.Dorsal spinocerebellar tract

posterolateral t.Lissauer tract.

pyramidal t.The corticobulbar and corticospinal tracts, which are the major direct outputs of the motor cortex. In cross-sections of the hindbrain, the pyramidal tract has a triangular shape.

reproductive t.Genital tract.

respiratory t.The respiratory passageway from mouth and nose to the alveoli in the lungs, divided into upper (above the vocal folds) and lower (below the vocal folds) parts.

reticulospinal t.Either of two tracts: the pontine reticulospinal tract or the medullary reticulospinal tract. The pontine reticulospinal tract contains axons originating in the pontine reticular formation; the axons run into the spinal cord along the ventral midline (the medial part of the anterior funiculus). The medullary reticulospinal tract contains axons originating in the medial two thirds of the hindbrain reticular formation; these axons run into the spinal cord in the anterior part of the lateral funiculus.

retinohypothalamic t.The retinal ganglion cell axons from the optic nerves that leave the optic tract at the optic chiasm to innervate the suprachiasmatic nucleus (in the hypothalamus), which contains the pacemaker cells for circadian rhythms.

rubrospinal t.An axon tract originating in the red nucleus of the midbrain. After leaving the red nucleus, axons cross to the contralateral side and descend into the spinal cord, where they terminate in the anterior horns. The red nucleus is innervated by axons from the motor cortices and the cerebellum, and the rubrospinal pathway is an extrapyramidal route to the spinal cord. A major function of rubrospinal axons is to set and adjust the muscle tone in the flexor muscles.

sensory t.Any axon tract, usually traveling rostrally in the CNS, that transmits information related to somatic or visceral sensation.

solitary t.Tractus solitarius.

spinal t. of the trigeminal nerve A tract of somatic sensory axons from the trigeminal nerve that runs caudally from the midpontine level of the brainstem along the spinal nucleus of the trigeminal nerve. The tract carries pain and temperature information from the face, and its axons synapse topographically in the adjacent nucleus. In the transition zone between hindbrain and spinal cord, the spinal tract of the trigeminal nerve disappears into the tract of Lissauer although a few axons of the spinal tract extend as far caudally as spinal cord segment C3-C4. SYN: trigeminal spinal tract.

spinocerebellar t.The dorsal or the ventral spinocerebellar tract.

spinothalamic t.The lateral or the anterior spinothalamic tract. Both tracts are bundles of axons running rostrally in the anterolateral quadrant (the anterior aspect of the lateral funiculus) of the spinal cord, originating from contralateral posterior horn neurons, and synapsing in the ventral posterolateral nucleus of the thalamus. The lateral spinothalamic tract carries pain and temperature information from the body; the anterior spinothalamic tract carries crude touch.

supraopticohypophyseal t.

Variant: supraopticohypophysial tract