Corticospinal pathways > Lateral corticospinal tract

This image is of the corticospinal pathway through the brainstem, shown in a series of transverse cross sections - note the position of the lateral corticospinal tract.

Lateral corticospinal tract:

• Consists of descending axons of neurons located in the motor cortex and (unexpectedly) some neighbouring areas of the cortex (premotor and somatosensory cortices which together contribute about 50% of its axons, the other 50% coming from the motor cortex itself).
  
• The axons of this tract terminate on motor neurons in the spinal cord ventral (anterior) horns either directly, or (more usually) indirectly via interneurons (enabling inhibition of spinal cord motor neurons as well as excitation).
• The corticospinal tract neurons are upper motor neurons, i.e. they are entirely within the CNS. The spinal motor neurons are lower motor neurons whose axons pass into the peripheral nerves and innervate muscles.
• From cortical neurons, axons pass through the posterior limb of the internal capsule, then the crus cerebri of the midbrain, then the pons and into the medulla (in the pyramids) where the tract divides into the large lateral corticospinal tract and a much smaller anterior (ventral) corticospinal tract.
• Is by far the largest (85%) of the two and is the main pathway for executing voluntary movements. It decussates in the ventral part of the medulla to descend in the spinal cord in the lateral white column on the opposite side. In most cases its axons synapse with motor neurons via interneurons, but those serving hand and some arm muscles end directly, providing very precise control (fractionating control).