SNARE proteins, present on both synaptic vesicles and the presynaptic membrane, aid in the fusion of vesicles with the presynaptic membrane, facilitating the release of acetylcholine into the synaptic cleft.

Ligand-gated ion channels are receptor proteins on the postsynaptic membrane that open in response to binding of a neurotransmitter.

They allow specific ions, like sodium ions, to pass through the membrane, leading to depolarisation.

Ligand-gated ion channels close after neurotransmitter binding to prevent continuous depolarisation of the postsynaptic neurone, ensuring that the response is not permanent.

Choline is reabsorbed into the presynaptic neurone, where it reacts with acetyl coenzyme A to reform acetylcholine.

The reformed acetylcholine is then transported into the presynaptic vesicles, ready for the next action potential.

After triggering an action potential in the postsynaptic neurone or muscle cell, the enzyme acetylcholinesterase catalyses the hydrolysis of acetylcholine into choline and ethanoic acid (acetate).

The breakdown products are reabsorbed into the presynaptic knob for recycling.

It is important to remove neurotransmitter from the synaptic cleft to prevent the stimulus from being maintained and to allow another stimulus to affect the synapse.

This prevents continuous stimulation and allows for neurotransmitter recycling.

1. An action potential reaches the presynaptic knob, depolarising the presynaptic membrane
2. Calcium ion (Ca²⁺) channels open and Ca²⁺ diffuses into the presynaptic knob
3. Synaptic vesicles fuse with the presynaptic membrane
4. Synaptic vesicles release neurotransmitter into the synaptic cleft by exocytosis, and neurotransmitters diffuse across the synaptic cleft
5. Neurotransmitters bind with specific receptors on the postsynaptic membrane and receptors change shape
6. Sodium ion (Na⁺) channels open in response to binding, and Na⁺ enters the postsynaptic neurone depolarising it
7. If this passes a threshold level, it triggers an action potential in the postsynaptic neurone

Cholinergic synapses are those that use the neurotransmitter acetylcholine.