Electrophysiologic testing of neuromuscular transmission

Abstract

The number of ACh-containing vesicles released by the presynaptic neuron is dependent on the existing number of vesicles ready for immediate release before depolarization, the concentration of calcium in the extra- and intracellular milieu, and the amplitude and duration of the presynaptic membrane depolarization. When the presynaptic membrane is depolarized, calcium enters the cell and activates the intracellular protein calmodulin. Activated calmodulin binds with a protein receptor next to the active zone, allowing movement of the vesicles toward the active zone. The number of vesicles released far exceeds the number needed to activate a propagated action potential in the muscle cell membrane (safety factor).