Motor neuron, electrophysiology

Degenerating axons in the peripheral nerves can also be examined as described below, and electrophysiological estimates of motor unit number could be informative. Motor units are defined as a single motor neuron (axon) and the muscle fibers its terminals innervate. In motor neuron diseases, the number of motor units is anticipated to decrease as motor neurons die, but the size of motor units may increase with compensatory sprouting and reinnervation (e.g., (1)). Interpretation can be further confounded by factors such as a change in muscle fiber number or innervation of muscle fibers by multiple motor axons. Therefore, the best interpretation results from corroborating evidence from the spinal cord, nerve, synapse, and the muscle. 

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