pyramidal tract

tract (trakt)

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.

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alimentary tract  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.

digestive tract  alimentary canal.

dorsolateral tract  a group of nerve fibers in the lateral funiculus of the spinal cord dorsal to the posterior column.

extracorticospinal tract , extrapyramidal tract extrapyramidal system.

Flechsig's tract  posterior spinocerebellar t.

gastrointestinal tract  the stomach and intestine in continuity.

genitourinary tract  urogenital system.

Gowers' tract  anterior spinocerebellar t.

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.

respiratory tract  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.

urinary tract 

1. see under system.

2. sometimes more specifically the conduits leading from the pelvis of the kidneys to the urinary meatus.

urogenital tract  see under system.

uveal tract  the vascular tunic of the eye, comprising the choroid, ciliary body, and iris.

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pyramidal tract

n.

A massive bundle of fibers that originates from the motor cortex and the postcentral gyrus and emerges on the ventral surface of the medulla oblongata. Most of the fibers cross to the opposite side in the pyramidal decussation and descend the length of the spinal cord to innervate muscles of the extremities.

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pyramidal tract,

a pathway composed of groups of nerve fibers in the white matter of the spinal cord through which motor impulses are conducted to the anterior horn cells from the opposite side of the brain. These descending fibers, the nerve cell bodies of which are found in the precentral cortex, regulate the voluntary and reflex activity of the muscles through the anterior horn cells.