A synapse is the junction between two neurones, or between a neurone and an effector, across which a chemical transmitter carries the signal.

Which ion enters the presynaptic knob when an action potential arrives, and through what?

Calcium ions enter through voltage-gated calcium channels that open when the presynaptic membrane depolarises.

What does the influx of calcium ions cause in the presynaptic knob?

It causes vesicles of neurotransmitter to move to the presynaptic membrane and fuse with it, releasing their contents into the cleft by exocytosis.

What happens when acetylcholine binds to a receptor on the postsynaptic membrane?

The receptor acts as a chemically gated channel that opens, allowing sodium ions into the postsynaptic neurone and depolarising it.

Which enzyme breaks down acetylcholine, and why is its action essential?

Acetylcholinesterase hydrolyses acetylcholine in the cleft, which is essential so that the postsynaptic neurone is not stimulated continuously and the synapse can respond to the next impulse.

OCR A-Level Biology B H422

The Developing Cell: Cell Division and Cell Differentiation

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The Nervous System and the Identification and Consequences of Damage

Synapses and the integration of responses

3 things to know
Components 01, 02 and 03

Overview

Recall questions on synaptic structure, calcium ions and neurotransmitter release, acetylcholine and acetylcholinesterase, one-way transmission, excitatory and inhibitory postsynaptic potentials, spatial and temporal summation, and divergence in integrating responses.

What you need to know

Answer each one before you reveal it.

Your recallNot started

Process

Describe what happens at a cholinergic synapse from the arrival of an impulse to the recycling of the transmitter.

Key term

What is a synapse?

Key term

Why does a presynaptic knob contain many mitochondria?

Questions from this subtopic

Each one with the model answer underneath.

1
What is a synapse?
Model answer
A synapse is the junction between two neurones, or between a neurone and an effector, across which a chemical transmitter carries the signal.
2
Why does a presynaptic knob contain many mitochondria?
Model answer
ATP from the mitochondria is needed to synthesise neurotransmitter, load it into vesicles and recycle the breakdown products.
3
Which ion enters the presynaptic knob when an action potential arrives, and through what?
Model answer
Calcium ions enter through voltage-gated calcium channels that open when the presynaptic membrane depolarises.
4
What does the influx of calcium ions cause in the presynaptic knob?
Model answer
It causes vesicles of neurotransmitter to move to the presynaptic membrane and fuse with it, releasing their contents into the cleft by exocytosis.
5
What happens when acetylcholine binds to a receptor on the postsynaptic membrane?
Model answer
The receptor acts as a chemically gated channel that opens, allowing sodium ions into the postsynaptic neurone and depolarising it.
6
Which enzyme breaks down acetylcholine, and why is its action essential?
Model answer
Acetylcholinesterase hydrolyses acetylcholine in the cleft, which is essential so that the postsynaptic neurone is not stimulated continuously and the synapse can respond to the next impulse.

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