Motor Nerve or Motor Neuron
The motor nerve, also call a motor neuron consists of four main parts: the dendrite, cell body, nucleus and axon. The dendrites branch out from the cell body and receive electrochemical signals from the brain and spinal cord. These signals control the triggering of the motor neuron. The cell body contains all of the functions that keep the cell alive and operating, including the nucleus that controls the activities of the cell. The axon, or nerve fiber, is a long, thin fiber. It conducts electrical impulses that signals the muscles to contract.
In humans and other vertebrates, a motor neuron can only cause muscle contraction. Motor neurons can not directly cause muscles to relax. Muscle relaxation is caused by inhibiting the motor neurons from firing.