Structurally, it encompasses the precentral gyrus in the cortical area frontal to the central sulcus in each hemisphere and extends in an anterior direction across the frontal lobes. A distinctive anatomical feature of the primary motor cortex is the presence of giant pyramidal cells in the fifth layer of the cerebral cortex [the largest neurons in the cortex and also referred to as Betz cells after their discoverer Vladimir Aleksandrovich Betz (1834-1894)]. Its axons form the corticospinal tract. As these neurons project to several other neurons, the ‘motor maps’ are rather imprecise in that stimulation of a cortical region results in activity in a large number of muscles, and a given muscle can be activated by stimulation across a wide range of the cortex. The premotor cortex and supplementary motor area together form the secondary motor cortex. Functionally, expressed in terms of topographical representations (or motor maps), it generates contralateral face, arm, trunk, and leg movements. Furthermore, it is involved in the control of voluntary movements. Having extensive connections with the somatosensory cortex in the parietal lobe, it ensures that movements can be modulated via fast sensory feedback. Like the visual cortex, if has a columnar organization such that cells in each column control the same group of muscles while adjacent columns control opposing muscle groups. Such an arrangement facilitates lateral inhibitory interactions among adjacent columns (e.g., the ‘biceps column’ inhibits the ‘triceps column’ and vice versa).
See Agonist muscle, Antagonist muscle, Cortical lobes, Corticospinal tract (CST), Direct corticomotoneuronal connections or tracts, Extrapyramidal system, Gyrus, Motor cortex, Premotor cortex, Somatosensory cortex, Supplementary motor area (SMA), Visual cortex