Point 4 Intro Pathway Deficits Spindles Summary Problems Contents Anatomy

Cells in the cerebral cortex, especially the motor cortex (area 4; precentral gyrus) possess very long axons that descend through an extensive region of the brain to eventually reach the spinal cord. Right before entering the cord these corticospinal fibers cross or decussate (L., to make an X) and enter the LATERAL FUNICULUS where they travel medial to the DSCT. These fibers, which are now called the lateral (they are in the lateral funiculus) corticospinal tract (LCST), innervate neurons in the spinal cord along its entire length. Once in the grey matter (where the cells are) LCST axons synapse upon cells in the ventral horn. This is the first synapse in a pathway over which the cerebral cortex informs cells in the CONTRALATERAL spinal cord about a voluntary movement that it wishes to perform. Once the cells in the ventral horn receive this cortical information, they directly drive the muscles via axons that pass out the ventral root. The fastest way you can move a body muscle voluntarily is by utilizing 2 neurons. The first one lies in the cerebral cortex, the second in the contralateral or opposite ventral horn. Descending fibers in the LCST are somatotopically organized such that the most medially located fibers in the tract terminate before (rostral to) the more the laterally placed fibers.