Corticospinal Tract Lesion

The corticospinal tract controls primary motor activity for the somatic motor system from the neck to the feet. It is the major spinal pathway involved in voluntary movements. The tract begins in the primary motor cortex, where the soma of pyramidal neurons are located within cortical layer V. Axons for these neurons travel in bundles through the internal capsule, cerebral peduncles, and ventral pons. They stay in the ventral position within the medulla as the pyramids. A majority of the axons cross the midline at the pyramidal decussation between the brainstem and spinal cord to form the lateral corticospinal tract (Figure 1A). This crossover causes the left side of the brain to control the right side of the spinal cord and the right side of the brain to control the left side of the spinal cord. A small number of axons remain on the ipsilateral side to form the anterior corticospinal tract. Axons of both anterior and lateral corticospinal tracts move into the gray matter of the ventral horn to synapse onto lower motor neurons. These lower motor neurons exit the spinal cord to contract muscle. While the anterior corticospinal tract assists with axial muscle motor control, the lateral corticospinal tract is the primary pathway for motor information to the body. Injuries to the lateral corticospinal tract results in ipsilateral paralysis (inability to move), paresis (decreased motor strength), and hypertonia (increased tone) for muscles innervated caudal to the level of injury. The lateral corticospinal tract can suffer damage in a variety of ways. The most common types of injury are central cord syndrome, Brown-Sequard syndrome, and anterior spinal cord syndrome.