Describe the sequence of events involved in transmission across a cholinergic synapse - AQA - A-Level Biology - Question 5 - 2020 - Paper 2
Question 5
Describe the sequence of events involved in transmission across a cholinergic synapse.
Do not include details on the breakdown of acetylcholine in your answer.
Worked Solution & Example Answer:Describe the sequence of events involved in transmission across a cholinergic synapse - AQA - A-Level Biology - Question 5 - 2020 - Paper 2
Step 1
Depolarisation of presynaptic membrane
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Answer
The process begins with the depolarisation of the presynaptic membrane, often initiated by an action potential reaching the synaptic knob.
Step 2
Calcium channels open and calcium ions enter (synaptic knob)
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As the membrane depolarises, voltage-gated calcium channels open, allowing calcium ions (Ca²⁺) to flow into the presynaptic terminal.
Step 3
(Calcium ions cause) synaptic vesicles move to fuse with presynaptic membrane and release acetylcholine/neurotransmitter
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Answer
The influx of calcium ions triggers synaptic vesicles containing acetylcholine to move towards the presynaptic membrane, where they fuse and release the neurotransmitter into the synaptic cleft.
Step 4
Acetylcholine/neurotransmitter diffuses across (synaptic cleft)
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Acetylcholine then diffuses across the synaptic cleft to the postsynaptic membrane.
Step 5
(Acetylcholine attaches to) receptors on the postsynaptic membrane
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Finally, acetylcholine binds to specific receptors on the postsynaptic membrane, triggering the opening of sodium ion channels.
