corticospinal tract
Jump to navigation
Jump to search
Structure
- massive bundle of myelinated nerve fibers
Origin
- originates from pyramidal cells in the 5th layer of the motor cortex (Brodman's areas 4 [including Betz cells] & 6) & to a lesser extent, the postcentral gyrus (somatosensory)
Innervation
- fibers from the lateral corticospinal tract are distributed throughout the length of the spinal cord to interneurons of the zona intermedia (spinal cord gray matter)
- fibers from the anterior corticospinal tract are distributed to interneurons in the medial aspect of the anterior horn on both sides
Course
- fibers from the cerebral cortex descend through the internal capsule, the middle 1/3 of the crus cerebri & the ventral part of the pons, emerging on the ventral surface of the medulla oblongata as the pyramids
- continuing caudally, most fibers cross the midline in the decussation of the pyramids, then descend in the lateral 1/2 of the spinal cord as the lateral corticospinal tract
- uncrossed fibers form a smaller anterior corticospinal tract, which descends in the anteromedial spinal cord
Pathology
- interruption of the corticospinal tract above the decussation of the pyramids in the medulla causes impairment of movement on the opposite side of the body (hemiplegia), especially severe in the extremities
- below the decussation of the pyramids, lesions of the lateral corticospinal tract cause ipsilateral hemiplegia
- a lesion of the corticospinal tract is characterized by muscular weakness, spasticity, hyper-reflexia & a positive Babinski sign
- a loss of sensation at or below the site of injury may occur[2]