Motor neurone

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(NB - for Motor Neurone Disease, see Motor neurone disease.)

A motor neurone (motor neuron, motorneuron, usually means lower motor neurone) is an efferent CNS neuron that innervates muscles and glands with muscles and controls their contractions. Their cell body is classically located in the spinal cord and the axon projects outside the spinal cord. However upper motor neurones of the cortex control the lower motor neurons and in the case of the facial nerve directly innervate some (facial) muscle. Human motor neurons use acetylcholine as their neurotransmitter. Subtypes of motor neurones include:

  1. Alpha motor neurones (ventral horn cells)
    • Innervate extrafusal muscle fibers, which are the main force-generating component of a muscle
  2. Beta motor neurones
    • Innervate intrafusal muscle fibers of muscle spindles
  3. Gamma motor neurones
    • Innervate intrafusal muscle fibers within the muscle spindle and regulate the sensitivity of the spindle to muscle stretching

The other main classification is into:

  1. Somatic motor neurones
  2. Special visceral motor neurones
    • project their axons to facial and neck muscles (in man)
  3. General visceral motor neurones (visceral motor neurons)
    • Indirectly innervate cardiac muscle and smooth muscles of the arteries via synapse onto neurons located in ganglia of the autonomic nervous system.
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