= Motor neuron
A <motor neuron> is a <neuron> whose output drives or regulates an effector, commonly <muscle>. A somatic <motor neuron> carries <action potentials> along its <axon> to a <neuromuscular junction>, where release of <acetylcholine> promotes excitation of a <muscle> fibre. Neural excitation, transmitter release and <muscle> force are successive steps. <Anatomy and Physiology 2e by J. Gordon Betts and others>[Sections 10.3 and 12.2: neuromuscular junction and functional neuron types]{ref}
A <reflex> illustrates the distinction between a sensory input and a motor output: a circuit converts an incoming signal into activity of an efferent <neuron>. The number and timing of motor-neuron impulses can change force without changing the identity of the contacted <muscle>. Clinical distinctions between upper and lower <motor neurons> refer to different positions in a motor pathway, so not every <neuron> involved in motor control directly innervates <muscle>.
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