The primary motor area is a group of networked cells in mammalian brains that controls movements of specific body parts associated with cell groups in that area of the brain. The area is closely linked by neural networks to corresponding areas in the primary somesthetic sensory area.
The primary motor area comprises the precentral gyrus and the related cortical tissue that folds into the central sulcus between the frontal lobes and the parietal lobes
Scientists have long considered arrangement of the primary motor area to be about the same in all mammals. In neurological terms, the area is described as M1.
In humans, the lateral area of the posterior prefrontal cortex (the side toward the back) is arranged from top to bottom in areas that correspond to the buttocks, torso, shoulder, elbow, wrist, fingers, thumb, eyelids, lips and jaw. Interior sections of the motor area folding into the medial longitudinal fissure correspond with the legs.
This arrangement, elucidated by Wilder Penfield and others, is called a motor homunculus (Latin: little man).
Not all body parts are equally represented by cell density in the motor area in proportion to their size in the body. Lips, parts of the face and hands enjoy especially large areas of cells in the motor area. Evidence suggests motor cells not used can be recruited by other cells to account for deficiencies arising from trauma such as amputation or paralysis.
The primary motor cortex (also known as M1) works in association with pre-motor areas to plan and execute movements. M1 contains large neurons known as Betz cells which send long axons down the spinal cord to synapse directly onto alpha motor neurons which connect to the muscles. Pre-motor areas are involved in planning actions (in concert with the basal ganglia) and refining movements based upon sensory input (this requires the cerebellum).