Motor cortex

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Overview of the cerebrum, the largest part of the brain.

The motor cortex is a region of the cerebral cortex involved in planning, controlling and execution of voluntary movements. It is an area of the frontal lobe located anterior to the central sulcus. 

The motor cortex comprises three different areas of the frontal lobe: the primary motor cortex (Brodmann’s area 4), the premotor cortex, and the supplementary motor area. 

The primary motor cortex or M1 is located on the precentral gyrus and anterior paracentral lobule on the medial surface of the cerebrum. It sends the majority of electrical impulses from the motor cortex and requires the least amount of electrical stimulation to elicit movements. Similar to its somatosensory counterpart, it is also somatotopically organized. This somatopic organization is represented by the motor homunculus which depicts the involvement of the primary motor cortex in producing movements of regions of the body. The representation of body parts which preform skilled and precise movements such as the hands and face are disproportionally large, therefore indicating that the primary motor cortex is involved in the control of voluntary, skilled or refined movements. Stimulation of the primary motor cortex results in the contraction of muscle groups on the opposite side of the body. 

The premotor cortex sits immediately anterior to the primary motor cortex and occupies Brodmann's area 6. Laterally, it occupies the posterior portions of the superior, middle and inferior frontal gyri. The main function of the premotor cortex is to prepare for movement, especially in proximally located musculature.

The medial surface of the premotor cortex presents another region known as the supplementary motor cortex. It is located on the medial surface of the longitudinal fissure just anterior to the 'leg' representation of the motor homunculus of the primary motor cortex. This area of the motor cortex is thought to be involved in body postural stabilization and coordination.

Stimulation of the premotor and supplementary cortical areas results in less refined, less focused movements of functionally related muscles. 

Once the motor cortex is stimulated, impulses are carried to the brainstem and spinal cord through descending tracts.