The motor cortex is a brain area that controls voluntary movements. It is fundamental for almost every physical action, from walking to speaking.
Anatomical Location
The motor cortex resides in the frontal lobe of the brain, positioned just in front of a significant groove known as the central sulcus. This places it on the brain’s surface, like a band extending over the top of the head. It is part of the cerebral cortex.
Within this broader motor cortex region, there are distinct areas, including the primary motor cortex (M1), the premotor cortex, and the supplementary motor area (SMA). The primary motor cortex is situated on the precentral gyrus. The premotor cortex lies immediately in front of the primary motor cortex, while the supplementary motor area is found on the medial surface of the longitudinal fissure. Each hemisphere of the motor cortex largely controls muscles on the opposite side of the body.
Functions of the Motor Cortex
The motor cortex is involved in the planning, initiation, and execution of voluntary movements. The primary motor cortex (M1) is the main area responsible for generating the neural impulses that travel down to the spinal cord to control movement execution. It sends direct commands to muscles through nerve cells that transmit instructions for body, facial, jaw, and tongue movements. The primary motor cortex is organized in a somatotopic manner, meaning specific areas correspond to different body parts; for instance, areas controlling the hands and face are disproportionately large due to their involvement in skilled, precise movements.
The premotor cortex and supplementary motor area contribute to more complex aspects of motor control, primarily involved in preparing and sequencing movements. The premotor cortex anticipates and plans movements based on external sensory cues, such as visual or auditory information, and helps guide movements by integrating sensory data. The supplementary motor area, by contrast, focuses on selecting and planning complex movements based on internal cues, such as memory or spontaneously learned actions, and is involved in coordinating bilateral movements. Both the premotor cortex and supplementary motor area send information to the primary motor cortex for execution, with some signals also traveling directly to the spinal cord.
The Motor Cortex and Coordinated Movement
The motor cortex does not function in isolation; it collaborates with other brain regions to produce smooth and coordinated movements. It forms intricate connections with areas like the cerebellum and the basal ganglia, which are also involved in motor control. The cerebellum plays a role in timing motor activities, ensuring a rapid and smooth progression between muscle movements, and is also involved in motor coordination and learning by detecting errors and generating corrective signals.
The basal ganglia, a group of subcortical nuclei, are involved in the selection and initiation of actions, as well as the execution of complex motor patterns. While traditionally thought to interact with the motor cortex primarily at the cortical level, recent research indicates direct communication pathways between the basal ganglia and the cerebellum, forming an integrated network. This interconnected system allows for the fine-tuning of movements, balance, and overall coordination, with the motor cortex acting as a central command hub within this complex network.