1. a region, principally one of some length.
2. a bundle of nerve fibers having a common origin, function, and termination.
3. a number of organs, arranged in series and serving a common function.
see under canal.
atriohisian tracts myocardial fibers that bypass the physiologic delay of the atrioventricular node and connect the atrium directly to the bundle of His, allowing preexcitation of the ventricle.
biliary tract the organs, ducts, etc., participating in secretion (the liver), storage (the gallbladder), and delivery (hepatic and bile ducts) of bile into the duodenum.
dorsolateral tract a group of nerve fibers in the lateral funiculus of the spinal cord dorsal to the posterior column.
gastrointestinal tract the stomach and intestine in continuity.
iliotibial tract a thickened longitudinal band of fascia lata extending from the tensor muscle downward to the lateral condyle of the tibia.
intestinal tract the small and large intestines in continuity.
nigrostriatal tract a bundle of nerve fibers extending from the substantia nigra to the globus pallidus and putamen in the corpus striatum; injury to it may be a cause of parkinsonism.
optic tract the nerve tract proceeding backward from the optic chiasm, around the cerebral peduncle, and dividing into a lateral and medial root, which end in the superior colliculus and lateral geniculate body, respectively.
pyramidal tract two groups of nerve fibers arising in the brain and passing down through the spinal cord to motor cells in the anterior horns.
see under system.
reticulospinal tract a group of fibers arising mostly from the reticular formation of the pons and medulla oblongata; chiefly homolateral, the fibers descend in the ventral and lateral funiculi to most levels of the spinal cord.
spinocerebellar tract, anterior a group of nerve fibers in the lateral funiculus of the spinal cord, arising mostly in the gray matter of the opposite side, and ascending to the cerebellum through the superior cerebellar peduncle.
spinocerebellar tract, posterior a group of nerve fibers in the lateral funiculus of the spinal cord, arising mostly from the nucleus thoracicus, and ascending to the cerebellum through the inferior cerebellar peduncle.
spinothalamic tract a group of nerve fibers in the lateral funiculus of the spinal cord that arise in the opposite gray matter and ascend to the thalamus, carrying the sensory impulses activated by pain and temperature.
2. sometimes more specifically the conduits leading from the pelvis of the kidneys to the urinary meatus.
see under system.
uveal tract the vascular tunic of the eye, comprising the choroid, ciliary body, and iris.
tract (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.
The anatomic region in the oral cavity and throat through which both air and food pass.
Any axon tract that carries information toward a particular target area.
alimentary tractDigestive tract.
anterior spinocerebellar tractVentral spinocerebellar tract.
An axon tract running rostrally in the spinal cord or brain, often a sensory pathway.
BILIARY TRACT (IN RELATION TO LIVER, PANCREAS, AND DUODENUM)
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: illustration; bile ducts; gallbladder; liver
Burdach tract See: Burdach, Karl
central tegmental tract
An axon tract connecting the subthalamus and the midbrain reticular formation with the inferior olivary nucleus.
An axon tract from the motor cortex that innervates the reticular formation and the cranial nerve nuclei in the hindbrain.
An axon tract from the frontal, parietal, and occipital cortices that innervates the hypothalamus.
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.
An axon tract originating in the external cuneate nucleus and synapsing in the ipsilateral cerebellum.
Any axon tract running caudally in the spinal cord or brain, often a motor pathway.
The continuous set of tubes that move food from the mouth to the anus. Synonym: alimentary tract
direct cerebellar tractDorsal spinocerebellar tract.
dorsal spinocerebellar tract
An ipsilateral (uncrossed) axon tract originating throughout Clarke's column in the spinal cord. The tract runs in the lateral funiculus of the spinal cord and terminates in the ipsilateral vermis of the cerebellum. Synonym: direct cerebellar tract
dorsolateral tractLissauer's tract.
Any axon tract that carries information away from a particular target area.
Any of the axon tracts of the extrapyramidal system. See: extrapyramidal system
A tract that passes from the cerebral cortex of the frontal lobe through the internal capsule and cerebral peduncle to the pons. Synonym: Arnold's bundle
The esophagus, stomach, and intestines.
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.
In males, the channels by which spermatozoa leave the body. In females, the channels in which the ovum grows and is fertilized and through which the baby leaves the body. Synonym: reproductive tract
The genital and urinary tracts together. Synonym: urogenital tract
A thickened band in the deep fascia along the lateral thigh (i.e., 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 lata muscles, both of which insert into it.
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.
The small and large intestines.
Lissauer's tract See: Lissauer's tract
lower gastrointestinal tract
The anus, rectum, colon, cecum, ileum and jejunum.
An axon tract originating in the mammillary body and synapsing in small nuclei near the caudal end of the midbrain tegmentum.
An axon tract originating in the mammillary body and synapsing in the anterior nucleus of the thalamus. The mammillothalamic tract is an integral component of the loop of neural circuits called the limbic system.
medullary reticulospinal tract See: reticulospinal tract
mesencephalic tract 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 reach the mandibular 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. Synonym: trigeminal mesencephalic tract
Any axon tract, usually running caudally in the CNS, that transmits output information.
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.
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.
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.
pontine reticulospinal tract See: reticulospinal tract
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 tractGenital tract.
The respiratory channel from mouth and nose to the alveoli in the lungs.
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.
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.
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 ventral 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.
Any axon tract, usually traveling rostrally in the CNS, that transmits information related to somatic or visceral sensation.
solitary tract Tractus solitarius.
spinal tract 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. Synonym: trigeminal spinal tract
The dorsal or the ventral spinocerebellar tract.
The lateral or the anterior spinothalamic tract. Both tracts are bundles of axons running rostrally in the ventrolateral quadrant (the ventral half of the lateral funiculus) of the spinal cord, originating from contralateral dorsal horn neurons, and synapsing in the ventral posterolateral (VPL) nucleus of the thalamus. The lateral spinothalamic tract carries pain and temperature information from the body; the anterior spinothalamic tract (adjacent and dorsal to the lateral tract) carries light touch information.
supraopticohypophyseal tract, supraopticohypophyial tract
A tract of fibers arising from cell bodies located in supraoptic and paraventricular nuclei of the hypothalamus and terminating in the posterior lobe of the hypophysis.
trigeminal mesencephalic tractMesencephalic tract of the trigeminal nerve.
trigeminal spinal tractSpinal tract of the trigeminal nerve.
trigeminothalamic tractTrigeminal lemniscus.
upper gastrointestinal tract
The esophagus, stomach, and duodenum.
The channel followed by urine in the body, from the glomeruli in the kidneys through the ureters, bladder, and urethra.
urogenital tractGenitourinary tract.
The vascular and pigmented tissues that constitute the middle layer of the wall of the eye. The tract comprises the iris, ciliary body, and choroid. Synonym: vascular tunic of the eye
ventral spinocerebellar tract
An axon tract originating in the contralateral dorsal and intermediate horns of the lower spinal cord, from the coccygeal through the lumbar segments. This tract runs in the lateral funiculus of the spinal cord, recrosses the midline, and terminates in the ipsilateral vermis of the cerebellum. Synonym: anterior spinocerebellar tract
ventricular outflow tract
In the heart, the pathway through which blood is normally ejected from the ventricle. For the left ventricle, it includes the walls of the ventricle, the anterior leaflet of the mitral valve, the aortic valve, the ascending aorta, and the arch of the aorta. For the right ventricle, it includes the walls of the ventricle, the pulmonic valve, the pulmonary trunk, and the pulmonary arteries.
An axon tract that conveys balance and equilibrium information to the spinal cord from the vestibular nuclei in the brainstem. The medial vestibulospinal tract is the continuation of the medial longitudinal fasciculus (MLF) caudally into the spinal cord below the cervical levels; it runs along the medial margin of the ventral quadrant of the cord. The lateral vestibulospinal tract runs caudally in an anterior band in the ventral and ventrolateral quadrant of the spinal cord.
The tissues and organs that produce human vocalizations, including lips, tongue, mouth, nasal cavities, pharynx, and larynx.