<P> At the primary motor cortex , motor representation is orderly arranged ( in an inverted fashion ) from the toe ( at the top of the cerebral hemisphere ) to mouth ( at the bottom ) along a fold in the cortex called the central sulcus . However , some body parts may be controlled by partially overlapping regions of cortex . Each cerebral hemisphere of the primary motor cortex only contains a motor representation of the opposite ( contralateral ) side of the body . The amount of primary motor cortex devoted to a body part is not proportional to the absolute size of the body surface , but , instead , to the relative density of cutaneous motor receptors on said body part . The density of cutaneous motor receptors on the body part is generally indicative of the necessary degree of precision of movement required at that body part . For this reason , the human hands and face have a much larger representation than the legs . </P>
the map size in the motor cortex is proportional to
the relative density of cutaneous motor receptors on said body part