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, which typically occurs due to an action potential firing down the axon.
Step 2
Calcium channels open and calcium ions enter (synaptic knob)
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As the presynaptic membrane depolarises, voltage-gated calcium channels open, allowing calcium ions (Ca2+) to flow into the synaptic knob.
Step 3
Calcium ions cause synaptic vesicles to move to fuse with presynaptic membrane and release acetylcholine/neurotransmitter
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Answer
The influx of calcium ions triggers synaptic vesicles filled with acetylcholine to move toward and fuse with the presynaptic membrane, releasing their contents into the synaptic cleft.
Step 4
Acetylcholine/neurotransmitter diffuses across (synaptic cleft)
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Once released, acetylcholine diffuses across the synaptic cleft towards the postsynaptic membrane.
Step 5
Acetylcholine attaches to receptors on the postsynaptic membrane
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The acetylcholine then binds to specific receptors on the postsynaptic membrane, leading to further depolarisation.
Step 6
Sodium ions enter (postsynaptic neurone) leading to depolarisation
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This binding causes sodium channels on the postsynaptic membrane to open, allowing sodium ions (Na+) to enter the postsynaptic neuron, further depolarising the membrane and potentially generating a new action potential.
