Britannica Sources used in this answer

Why does the left cerebral hemisphere control the right side of the body?

Created from Britannica articles using AI. AI can make mistakes, so verify using Britannica articles.

Diagram comparing action potential conduction in myelinated and unmyelinated axons, showing a neuron with labeled cell body, myelin sheath, nodes of Ranvier, and the flow of electrical signals along each type of axon. — nervous system In a myelinated axon, the myelin sheath prevents the local current (small black arrows) from flowing across the membrane. This forces the current to travel down the nerve fibre to the unmyelinated nodes of Ranvier, which have a high concentration of ion channels. Upon stimulation, these ion channels propagate the action potential (large green arrows) to the next node. Thus, the action potential jumps along the fibre as it is regenerated at each node, a process called saltatory conduction. In an unmyelinated axon, the action potential is propagated along the entire membrane, fading as it diffuses back through the membrane to the original depolarized region.

The left cerebral hemisphere controls the right side of the body because each cerebral hemisphere supplies motor function to the opposite, or contralateral, side of the body.1

This anatomical arrangement occurs because the nerve fibers responsible for motor control cross over to the opposite side of the body. A primary pathway for this movement is the corticospinal tract, which facilitates the coordination of muscles. The crossing of these motor fibers is known as the decussation of the pyramids. Consequently, the left hemisphere receives sensory input from and sends motor commands to the right half of the body, while the right hemisphere performs the same functions for the left half.231