Lateral corticospinal tract

At a glance

English

Lateral corticospinal tract

Latin (TA2)

Tractus corticospinalis lateralis

System

Nerve

Region

Whole body

Side

Single, on the midline

About the lateral corticospinal tract

Known also as the crossed pyramidal tract, the lateral corticospinal tract carries the bulk of the corticospinal fibres. It runs the whole length of the spinal cord in the lateral funiculus. In cross-section it forms an oval field just in front of the posterior horn, with the posterior spinocerebellar tract on its outer side and the lateral fasciculus proprius between it and the grey matter. It shrinks steadily as it descends, because fibres leave it at every level.

Its axons are those of upper motor neurons in the cerebral cortex, mainly the precentral gyrus, with contributions from premotor and parietal areas. They pass down through the internal capsule, the cerebral peduncle, the basilar pons and the medullary pyramid. At the lower end of the medulla, where it joins the cord, most of them cross the midline in the pyramidal decussation and settle in the opposite lateral funiculus. The fibres for the upper limb lie nearer the grey matter and those for the lower limb nearer the surface.

At each level fibres turn medially into the grey matter. Most end on interneurons of the intermediate zone, and some synapse directly on motor neurons in the lateral part of the anterior horn, the cells that drive the distal limb muscles. This direct link is what allows independent finger movement and precise control of the hand. Axial and girdle muscles are governed mainly by the anterior corticospinal tract.

Where a lesion lies decides which side is weak. Damage above the decussation, in the cortex, internal capsule or brainstem, weakens the opposite side of the body. Damage to the tract within the cord affects the same side below the level of injury. Either way, an upper motor neuron picture follows, with spasticity, brisk reflexes and an upgoing plantar response. In amyotrophic lateral sclerosis the tract degenerates together with the lower motor neurons, so signs of both appear together.

Course and supply

Supplies

Carries voluntary motor commands from the cerebral cortex of one side to the anterior horn of the opposite side of the cord, chiefly for skilled movement of the limbs and hand.

Blood supply

Lies deep in the lateral funiculus, supplied mainly by the anterior spinal artery with a smaller share from the arterial vasocorona at the surface.