Explain the neuromuscular junction

Action potential causes depolarisation in the presynaptic bulb, this causes voltage-gated calcium channels to open. This causes vesicles containing the neurotransmitter acetycholine to move and fuse with the presynaptic membrane, hence acetylcholine is released into the synaptic cleft by exocytosis. Acetylcholine diffuses across the synapse and bind to acetylcholine receptors on the post-synaptic membrane. This causes voltage-gated sodium channels on the sarcolemma to open and sodium from the synaptic cleft to move into the sarcoplasm causing depolarisation. This depolarisation spreads across the sarcoplasm by T-tubules. This depolarisation causes the sarcoplasmic reticulum to release calcium into the sarcoplasm, which will then be used by the muscles for contraction.