A-Level AQA Biology Nucleic Acids: Structure & DNA Replication: Describe the sequence of events

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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Answer

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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Answer

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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Answer

Finally, acetylcholine binds to specific receptors on the postsynaptic membrane, triggering the opening of sodium ion channels.

Describe the sequence of events involved in transmission across a cholinergic synapse - AQA - A-Level Biology - Question 5 - 2020 - Paper 2

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

Depolarisation of presynaptic membrane

Calcium channels open and calcium ions enter (synaptic knob)

(Calcium ions cause) synaptic vesicles move to fuse with presynaptic membrane and release acetylcholine/neurotransmitter

Acetylcholine/neurotransmitter diffuses across (synaptic cleft)

(Acetylcholine attaches to) receptors on the postsynaptic membrane

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