How does a nerve impulse cross a neuromuscular junction

When an action potential arrives at the junction, the depolarisation causes voltage-gated calcium channels to open resulting in the influx of calcium ions in to the pre-synaptic neurone. This triggers the movement of vesicles containing Acetylcholine to the membrane, leading to exocytosis of the neurotransmitter into the synapse. Acetylcholine diffuses across the synapse and binds to receptors on the muscle cell, this causes sodium channels to open. Sodium floods in to the muscle fibre causing a depolarisation. The action potential is then carried along the fibre to the T-tubles which help co-ordinate the muscle contraction. Acetylcholinesterase breaks down the neurotransmitter in the synapse ready for the next action potential.