<P> The primary motor cortex ( Brodmann area 4 ) is a brain region that in humans is located in the dorsal portion of the frontal lobe . It is the primary region of the motor system and works in association with other motor areas including premotor cortex , the supplementary motor area , posterior parietal cortex , and several subcortical brain regions , to plan and execute movements . Primary motor cortex is defined anatomically as the region of cortex that contains large neurons known as Betz cells . Betz cells , along with other cortical neurons , send long axons down the spinal cord to synapse onto the interneuron circuitry of the spinal cord and also directly onto the alpha motor neurons in the spinal cord which connect to the muscles . </P>
which body part ( s ) occupy the greatest portion of the primary motor cortex
a brain region that in humans is located in the dorsal portion of the frontal lobe