ABSTRACT

A large class of behaviors that fall between the intentional, voluntary movements controlled by the cerebral cortex and the reflexes controlled by the spine are programmed by various centers in the brain stem. The pathways by which the brain controls these motor neurons are complex, and what follows is a simplification. One major pathway is the pyramidal system. In one part of this, the corticospinal tract, axons from cortical neurons pass through the brain stem and down the spinal cord before synapsing with motor neurons. Individual movements are controlled by the primary motor cortex. This occupies the precentral gyrus, parallel to the somatosensory cortex in the postcentral gyrus. The main inputs to the primary motor cortex come from the premotor cortex and the supplementary motor area located in the gyrus anterior to the primary motor cortex. Together, these are sometimes called the secondary motor cortex.