Electrophysiological techniques are important in the evaluation of neuromuscular transmission. The amount of acetylcholine released by a nerve impulse--and thus the size of the endplate potential--is influenced by preceding activity in the junctional region. This normally is of little consequence, because the amount of acetylcholine released far exceeds that required to generate endplate potentials above the threshold for activating muscle fiber action potentials. Reduction in this safety factor, however, may alter the number of muscle fibers activated by an impulse and thus the size of the CMAP elicited by a supramaximal stimulus to the motor nerve. The size of the electrical response evoked in muscle by two or more supramaximal stimuli, or by a single stimulus applied after a 30-second period of maximal voluntary activity or tetanic stimulation, therefore reflects the efficacy of neuromuscular transmission.
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