If a certain threshold level is exceeded within the Na+
influx, the depolarization of the membrane causes an
Action potential to quickly change from – 80 mV up
to + 30 mV (Fig. 7). It is a monopolar electrical burst
that is immediately restored by the repolarization
phase and followed by an After Hyperpolarization
period of the membrane. Starting from the motor end
plates, the action potential spreads along the muscle
fiber in both directions and inside the muscle fiber
through a tubular system.