Which cortex controls voluntary movements on either side of the body, depending on the hemisphere?

• A. Primary Motor Cortex
• B. Premotor Cortex
• C. Parietal Cortex
• D. Frontal Lobe

Answer: (A)

The primary motor cortex is the brain region that directly commands voluntary movements. It sits in the precentral gyrus of the frontal lobe and sends signals to the muscles to produce motion.

Each hemisphere controls the opposite side of the body because the motor pathways cross over (decussate) in the brainstem. So stimulating or activating the left primary motor cortex would produce movement on the right side, and vice versa. This area also has a rough map of the body—the motor homunculus—showing which parts of the cortex control different muscles.

Other regions have related roles but not the direct command of voluntary movement. The premotor cortex helps plan and coordinate movements before they occur; the parietal cortex handles sensory integration and spatial processing; the frontal lobe is a broad region that includes motor areas but isn’t itself the specific site for issuing the direct movement commands.