motor neuron

one of the units or fibres of a MOTOR NERVE . An upper motor neuron is contained entirely within the CENTRAL NERVOUS SYSTEM , having its CELL body in the BRAIN and its AXON (a long process) extending into the SPINAL CORD where it SYNAPSES with other neurons. A lower motor neuron has its cell body in the spinal cord or brain stem and an axon that runs outwards via a spinal or cranial motor nerve to an effector muscle or gland.