Describe the events which normally occur between the arrival of an action potential at the synaptic knob and its transmission across a neuromuscular junction.

Voltage gated calcium channels open in response to the action potential reaching the presynaptic knob. Calcium ions diffuse into the celll down their concentration gradient. This results in synaptic vesicels moving towards the presynaptic membrane, where they fuse with the membrane, releasing their contents- the neurotransmitter Acetylcholine- into the synaptic cleft. The acetlycholine diffuses across the membrane and binds to acetylcholine receptors on the postsynaptic neuron. This triggers sodium ion channels to open on the postsynaptic neuron, allowing influx of sodium, down it's concentration gradient into the postsynaptic neuron which results in an action potential being generated in the postsynaptic neuron.