QS Study

Corticospinal Tract

Tracts are a bundle of nerve fibers within CNS have the same origin, same destination, and the same function.


Fibers of the corticospinal tract arise as axons of the pyramidal cell of Betz situated is the fifth layer of the cerebral cortex. It originates about 30% from the primary motor cortex, 30% from the premotor and supplementary motor areas and 40% from the somatosensory areas posterior to the central sulcus. They receive the same inputs as the corticospinal tracts. The fibers converge and pass through the internal capsule to the brainstem. Corticospinal tract arises from long axons of the pyramidal cells (extrapyramidal layer) of the precentral gyrus (primary motor center of the cerebral cortex).

The corticospinal tracts begin in the cerebral cortex, from which they receive a range of inputs:

  • Primary motor cortex
  • Premotor cortex
  • Supplementary motor area

They also receive nerve fibers from the somatosensory area, which play a role in regulating the activity of the ascending tracts. The primary purpose of the corticospinal tract is for voluntary motor control of the body and limbs.


After leaving cortex it passes through corona radiata then its course is started.

  • In internal capsule: Passes through the posterior limb of the internal capsule.
  • In Midbrain: Through middle 2/3rd of crus cerebral.
  • In pons: The track is broken into many bundles by the transverse pontocerebellar fibers.
  • In medulla: Forms the pyramid in the lower part of the medulla.
  • By far the majority fiber crosses the midline and a few fibers do not cross the opposite side.

Fig: Course of Corticospinal Tract

In spinal cord:

  • The crossed fibers descend lateral corticospinal tract.
  • Uncrossed fibers descend ipsilaterally as ventral corticospinal tract.
  • Some uncrossed fibers also descend through the lateral corticospinal tract.


Finally terminating –

Lateral corticospinal tract:

  • Principally or the interneurons in the intermediate regions of the cord gray matter.
  • A few on sensory relay neurons m the dorsal horn.
  • A very few directly on the anterior motor neurons that cause muscle contraction.

Ventral corticospinal tract: Most of these fibers also cross the minute and terminate in the anterior gray column of the spinal cord segments in the cervical and upper thoracic region.