Corticospinal tract or Pyramidal tract

 The corticospinal tract is a descending tract the fibers of which arise as axons from the cells situated in the fifth layer of cerebral cortex.

About one third i.e 30% fibers of the corticospinal tract arise from the Primary motor cortex and 30% fibers arise from both premotor and supplementary area, while the remaining 40% arise from the somatosensory area i.e postcentral gyrus lies posterior to the central sulcus.

Corticospinal tract in corona radiata:

  The corticospinal tract fibers after originating from the cerebral cortex descend downward and converge in the corona radiata and pass through posterior limb of the internal capsule.

Corticospinal tract in midbrain:

After leaving the forebrain the corticospinal tract enters the midbrain moves downward through a region of the midbrain called crus cerebri , in the middle three fourth of basis pedunculi of the midbrain.

Corticospinal tract in pons:

The corticospinal tract is broken down into many bundles by the transverse pontocerebral fibers as soon as it enters the pons.

Corticospinal tract in medulla:

After leaving the pons the corticospinal tract fibers are converged along the anterior border of medulla oblongata to form a swelling called pyramid that is why corticospinal tract is also called pyramidal tract. Majority of these fibers then cross to the opposite sides at the junction between medulla oblongata and spinal cord and descend downward as a Lateral corticospinal tract of the spinal cord. It terminate in the intermediate region of the cord gray matter.

Ventral corticospinal tract:

A few fibers of the corticospinal tract do not cross each other at the junction between the medulla oblongata and spinal cord and move downward on the same side of the spinal cord as a ventral corticospinal tract. It terminates in the anterior white column of the spinal cord.

Branches of corticospinal tract:

It gives lateral branches.

Branches to caudate and lentiform nuclei

Branches to red nuclei and olivary nuclei

Branches of the reticular formation.

These branches keep the subcortical region of brain informed of the cortical motor activity.