Explain the transmission of a nerve impulse across a cholinergic synapse referring to action potentials. (6)

When an action potential reaches the terminal of a pre-synaptic cleft, voltage-gated calcium channels are stimulated to open, causing an influx of Ca+ ions in the pre-synaptic neuron. This infux of Ca+ ions causes synaptic vesicles to fuse with the pre-synaptic membrane, releasing a neurotransmitter called acetyl choline by a process of exocytosis. The neurotransmitter diffuses across the synaptic cleft and binds to specific receptors in the post-synaptic membrane, stimulating sodium ion channels to open. The influx of of sodium ions causes depolarisation of the post synaptic membrane, which can initiate an action potential if the threshold is reached. Finally, the neurotransmitter is broken down by a specific enzyme in the synaptic cleft. The products of breakdown are absorbed by the pre-synaptic neuron by endosytosis and can be used to synthesise more neurotransmitter.