Describe the sequence of events involved in transmission across a cholinergic synapse - AQA - A-Level Biology - Question 5 - 2020 - Paper 1
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 1
Step 1
Depolarisation of presynaptic membrane
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Answer
The process begins with the depolarisation of the presynaptic membrane, triggered by an action potential that travels down the axon.
Step 2
Calcium channels open and calcium ions enter
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Answer
Following depolarisation, voltage-gated calcium channels open, allowing calcium ions ( ext{Ca}^{2+}) to flow into the presynaptic neuron.
Step 3
Synaptic vesicles fuse with presynaptic membrane
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The influx of calcium ions causes synaptic vesicles to move towards and fuse with the presynaptic membrane, leading to the release of acetylcholine (neurotransmitter) into the synaptic cleft.
Step 4
Acetylcholine diffuses across synaptic cleft
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Once released, acetylcholine diffuses across the synaptic cleft, the small gap between the presynaptic and postsynaptic membranes.
Step 5
Acetylcholine attaches to receptors on the postsynaptic membrane
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Acetylcholine then binds to specific receptors on the postsynaptic membrane, triggering a response in the postsynaptic neuron.
Step 6
Sodium ions enter leading to depolarisation
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This binding of acetylcholine opens sodium channels, allowing sodium ions ( ext{Na}^+) to enter the postsynaptic neuron, leading to its depolarisation.
