motor neuron

Photomicrograph of the body of a motor neuron. The cell nucleus and the sensory dendrites are clearly visible. The motor axon leaves at the bottom of the picture

One of the nerve cells (neurons) that goes to make up the nerve pathway (motor nerves) between the brain and an effector organ, such as a skeletal muscle. An upper motor neuron has a cell body in the brain and an axon that extends into the spinal cord, where it ends in synapses. It is thus entirely within the central nervous system. A lower motor neuron, on the other hand, has a cell body in the spinal cord or brainstem and an axon that extends outwards in a cranial or spinal motor nerve to reach an effector. See also sensory nerve.

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• ANATOMY AND PHYSIOLOGY

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