The steps of neuromuscular transmission are as follows:

(1) An action potential is conducted down the motor axon to the prejunctional axon terminal.

(2) Depolarization of the terminal buttons opens up voltage-gated Ca2+ channels in its membranes. Ca2+ moves into the terminals along an electrochemical gradient.

(3) Elevated Ca2+ concentration in the terminal button causes exocytosis of the ACh-containing synaptic vesicles in the terminal button into the myoneural cleft.

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(4) The acetylcholine released from the axon terminal then diffuses across the myoneural cleft and binds to a specific acetylcholine receptors on the motor end- plate.

(5) The binding of ACh with the ACh receptor (ACh-R) increases the conductance of the postjunctional membrane to Na+ and K+, resulting in a transient depolarization of the post­junctional membrane. This depolarization is called the endplate potential (EPP).

(6) The EPP is transient because acetylcholine is quickly hydrolyzed by the enzyme acetylcholinesterase (ACh-E) into choline and acetate. AChE is present in high concentration in the junctional cleft.

(7) The postjunctional membrane cannot generate action potentials.

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However, the EPP depolarizes the adjacent muscle membrane by electro tonic conduction. When the depolarization exceeds the threshold, an action potential is triggered in the adjacent muscle membrane.