Generatie van actiepotentiaal in skeletspieren

The resting membrane potential of a muscle cell is the difference in electrical charge across its membrane at rest. It is typically around -85 mV.

At a neuromuscular junction, when the acetylcholine released from the axon terminals binds the nicotinic receptors on the motor end plate, it allows sodium ion influx into the muscle fiber.

This influx makes the membrane potential less negative, leading to local depolarization at the motor end plate.

If this potential change crosses a threshold of -50 to -55 mV, it opens voltage-gated sodium channels, triggering an action potential — a self-propagating electrical signal.

The action potential starts a depolarization wave by opening adjacent voltage-gated sodium ion channels, propagating the signal along the entire muscle fiber.

After the depolarization of the membrane reaches its highest point of about +40 mV, also known as the overshoot, the voltage-gated sodium channels shut down.

Simultaneously, the overshoot potential opens the voltage-gated potassium channels for the exit of potassium ions, dropping the electric charge of the membrane back to its resting potential. This phase is called repolarization.