Anterior corticospinal tract

At a glance

English

Anterior corticospinal tract

Latin (TA2)

Tractus corticospinalis anterior

System

Nerve

Region

Whole body

Side

Single, on the midline

About the anterior corticospinal tract

The anterior corticospinal tract is the minor, uncrossed share of the great pyramidal pathway that runs from cortex to cord. It is also known as the ventral or direct pyramidal tract, or the bundle of Türck. In transverse section it forms a narrow strip in the anterior funiculus, pressed against the anterior median fissure. Its size varies from person to person, and it is large when the lateral corticospinal tract is small, and the reverse.

Its fibres begin as upper motor neurons in the motor cortex of the precentral gyrus. They descend through the internal capsule, the cerebral peduncle, the pons and the pyramid of the medulla together with the rest of the corticospinal system. At the pyramidal decussation, where most fibres cross, these stay on their own side and continue straight down into the anterior funiculus. The tract is present only in the cervical and upper thoracic cord; it thins as it goes and usually gives out around mid-thoracic levels.

Near the segment it serves, each fibre crosses the midline in the anterior white commissure and ends on interneurons and lower motor neurons in the anterior horn of the opposite side, so the final effect is still on the side opposite the cortex. A few fibres instead stay on the same side or pass to the lateral funiculus and the base of the posterior horn. The lower motor neuron then passes the command on to the muscle fibres.

Because its targets are the medial motor columns, the tract chiefly governs the axial and girdle muscles of the neck and trunk, whereas the lateral tract handles the fine control of the limbs. Its partly bilateral influence on trunk muscles helps explain why posture of the trunk is often relatively preserved after a one-sided cortical stroke, while hand and arm control on the opposite side is badly affected.

Course and supply

Supplies

Carries voluntary motor commands from the motor cortex to the anterior horn cells that supply the muscles of the neck and trunk, crossing at segmental level.

Blood supply

Lies in the anterior funiculus, within the territory of the anterior spinal artery.