Motor nerve

Motor nerves carry information from the central nervous system to the muscles. The signals for this originate in the motor area of the cerebrum. These signals descend via the cerebellum and the brainstem to the spinal cord. The cell body of a motor nerve remains in the central nervous system; via a long projection, it finally reaches the muscle.

To move, muscles must receive a command to do so. This control is managed by the brain and motor nerves. The senses perceive stimuli from the environment and pass these signals via sensory nerves to the central nervous system. The central nervous system then sends signals to the muscles to initiate action.

For example, consider driving a nail into a plank. First, our senses, such as the eyes, explore the environment. The sensory nerves in the arm determine the arm's position and send this information to the brain. The brain processes the signal into a movement, and via motor nerves, the appropriate muscles are tensed. The result: reaching for the hammer, lifting it, and hitting the nail with exactly the right force.

This is the voluntary part of the motor nerves. However, these nerves also play a role in the body's involuntary movements, meaning unconscious actions such as contracting the heart muscle. This happens completely automatically. It is impossible to generate a signal in the brain that travels via the motor nerve to the heart to stop it or make it work harder.

The motor cortex in the cerebrum consists of a left and a right half. The nerve tracts originating from this area cross over before entering the spinal cord. This crossing ensures that in people with a stroke in the right hemisphere of the brain, the left side of the body is affected.