At the neuromuscular junction, acetylcholine release leads to sodium influx and depolarization, creating an end-plate potential. This sequence is described as which event?

• A. Generation of an end-plate potential
• B. End-plate depolarization
• C. Action potential
• D. Resting potential

Answer: (A)

The event described is the generation of an end-plate potential. When acetylcholine is released at the neuromuscular junction, it binds to nicotinic receptors on the motor end plate, opening Na+ (and other cation) channels. The resulting influx of sodium locally depolarizes the muscle fiber membrane right under the nerve terminal, creating a graded potential called the end-plate potential. This is a local, non-propagated depolarization that can trigger a muscle fiber action potential if it reaches threshold, but on its own it is the generation of the end-plate potential, not the action potential itself. Resting potential is simply the baseline membrane potential when no transmitter signal is present.