When Ach is released from the presynaptic membrane, it binds to channel-shaped receptor molecules on the end plate, opening the channels and allowing positively charged sodium ions to flow into the muscle cell, which causes the membrane to depolarise slightly. An enzyme called acetylcholinesterase then rapidly degrades the acetylcholine, so they can diffuse back to the presynaptic knob, closing the channels and allowing the membrane to return to its previous polarised state. 
- ↑ Alberts, Johnson, Lewis, Morgan, Raff, Roberts and Walter (2015) Molecular biology of the cell 6th Edition. New York. Garland Science, Taylor and Francis Group.