tractus pyramidalis

1. [TA] pyramidal tract: a term generally applied to several groups of fibers (corticonuclear, corticospinal, and corticoreticular) arising chiefly in the sensorimotor regions of the cerebral cortex and descending in the internal capsule, cerebral peduncle, and pons to the medulla oblongata, the corticoreticular fibers descending with the corticospinal fibers and synapsing with cells of the reticular formation and the corticonuclear fibers synapsing with motor nuclei throughout the brainstem. Most of the corticospinal fibers cross in the decussation of the pyramids and descend in the spinal cord as the lateral corticospinal tract; most of the uncrossed fibers form the anterior corticospinal tract; both end by synapsing with internuncial and motor neurons. The pyramidal tract is a phylogenetically new tract, most prominent in humans, and provides for direct cortical control and initiation of skilled movements, especially those related to speech and involving the hand and fingers. Called also corticospinal tract of medulla oblongata, fasciculus pyramidalis medullae oblongatae, and pyramidal system. 2. either of the corticospinal tracts of the spinal cord; see t. corticospinalis anterior and t. corticospinalis lateralis.