The motor areas of the brain are located in both hemispheres of the cortex. They are positioned like a pair of headphones stretching from ear to ear. The motor areas are very closely related to the control of voluntary movements, especially fine movements performed by the hand. The right half of the motor area controls the left side of the body, and the left half of the motor area controls the right side of the body.

Motor Cortex Divisions

The motor cortex is divided into three areas:

1. Primary motor cortex: Main contributor to the generation of neural impulses that control the execution of movement.

2. Premotor cortex: Located anterior to the primary motor cortex and responsible for some aspects of motor control. 

3. Supplementary motor area (SMA): Functions include internally generated planning of movement, planning of sequences of movement, and the coordination of the two sides of the body. It is located on the midline surface of the hemisphere anterior to the primary motor cortex.

Motor Cortex

$$Topography of the human motor cortex, including the premotor cortex, SMA, primary motor cortex, primary somatosensory cortex, and posterior parietal cortex.

Motor Cortex Functions

Motor functions are also controlled by these additional structures:

Posterior parietal cortex – Guides planned movements, spatial reasoning, and attention.

Dorsolateral prefrontal cortex – Important for executive functions, including working memory, cognitive flexibility, and abstract reasoning.

Buried deep in the white matter of the cerebral cortex are interconnected subcortical masses of cerebral gray matter called basal nuclei (or basal ganglia) that are involved in motor control. The basal nuclei receive input from the substantia nigra of the midbrain and motor areas of the cerebral cortex and send signals back to both of these locations. 

Motor Cortex Map

The majority of neurons in the motor cortex project to the spinal cord synapse on interneuron circuitry in the spinal cord. The view that each point in the motor cortex controls a muscle or a limited set of related muscles has been debated. Various experiments examining the motor cortex map showed that each point in motor cortex influences a range of muscles and joints, indicating significant overlapping in the map.

Cortex Map

Map of the body in the human brain.

This map of the motor cortex indicates the regions of the brain that control specific areas of the body and actions, including tongue, lips, squint, fingers, wrist, forearm, elbow, foot, and saccade.