Put the following events of the neuromuscular junction in the order in which they occur.
1) Action potential is propagated in the sarcolemma.
2) Acetylcholine binds to ligand gated sodium channels.
3) Action potential arrives at the neuromuscular junction.
4) Vesicles full of acetylcholine are stored at the axon terminal.
5) Acetylcholine is released into the synaptic cleft.