What happens in the muscle postsynaptically during neuromuscular transmission?
The binding of two ACh molecules to each ACh receptor (AChR) in the muscle (postsynaptic) membrane opens a Na + channel within the receptor, allowing Na + influx, which generates subthreshold depolarizations known as miniature endplate potentials (MEPPs).
The MEPPs in each muscle fiber summate to form the endplate potential (EPP) for that fiber.
When a sufficient number of receptors are activated simultaneously, the EPP becomes large enough to trigger an action potential, which then propagates along the muscle sarcoplasmic membrane to the T-tubule system, leading to the release of Ca 2+ from the sarcoplasmic reticulum and muscle contraction.
