Explain the process of synaptic transmission (6 marks).

When the action potential reaches the pre-synaptic knob, voltage gated Ca²⁺ channels open which allows Ca²⁺ into the pre-synaptic knob - This causes vesicles which contain neurotransmitter such as acetylcholine to migrate to the cell membrane where they fuse and release the neurotransmitter into the synaptic cleft -The neurotransmitter diffuses across the cleft and binds to receptos on the post-synaptic neuron -This causes Na⁺ channels to open which allows Na⁺into the post-synaptic neuron which causes cell depolarisation -If threshold is reached then then the action potential will be propegated along the post-synaptic neuron - The neurotransmitter then needs to be cleared from the cleft in order for further signals to be transmitted - This can be done by enzymes such as acetylecholinesterase wgicg hydrolyses (breaks down) acetylcholine -Neurotransmitters may also be transported back into the pre-synaptic knob by pumps