The motor area or motor cortex is the side of the brain that controls voluntary muscles. The motor cortex governs the body’s response to messages from the outside world. The motor nerves twine through muscle fibers like a root system that ends in clusters called motor end plates. These fibers start muscle contractions by means of chemical messengers. The motor area is divided between the two sides of the brain, called hemispheres, which are different in size, shape and the roles they play. The right hemisphere controls the motor responses in the left side of the body and the left hemisphere controls the right side.