What is spatial summation?

Spatial summation occurs when impulses from multiple presynaptic neurones arrive at the same postsynaptic neurone simultaneously.

What is temporal summation?

Temporal summation occurs when repeated impulses from a single presynaptic neurone arrive in quick succession at the same postsynaptic neurone.

What effect do excitatory synapses have on the postsynaptic membrane?

Excitatory synapses release neurotransmitters that cause depolarisation of the postsynaptic membrane, making an action potential more likely.

What effect do inhibitory synapses have on the postsynaptic membrane?

Inhibitory synapses release neurotransmitters that cause hyperpolarisation of the postsynaptic membrane, making an action potential less likely.

How do inhibitory neurotransmitters cause hyperpolarisation?

Inhibitory neurotransmitters cause chloride ion channels to open, allowing Cl⁻ to enter, or potassium channels to open, allowing K⁺ to leave; both cause hyperpolarisation.

OCR A-Level Biology H420

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Neuronal Communication

Summation and inhibitory synapses

1 thing to know
Components 01 and 03

Overview

Spatial and temporal summation, the difference between excitatory and inhibitory synapses, and how a postsynaptic neurone decides whether to fire.

What you need to know

Answer each one before you reveal it.

Your recallNot started

Key term

Define summation in the context of synaptic transmission.

Questions from this subtopic

Each one with the model answer underneath.

1
Define summation in the context of synaptic transmission.
Model answer
Summation is the process by which multiple small depolarisations combine to reach the threshold and trigger an action potential.
2
What is spatial summation?
Model answer
Spatial summation occurs when impulses from multiple presynaptic neurones arrive at the same postsynaptic neurone simultaneously.
3
What is temporal summation?
Model answer
Temporal summation occurs when repeated impulses from a single presynaptic neurone arrive in quick succession at the same postsynaptic neurone.
4
What effect do excitatory synapses have on the postsynaptic membrane?
Model answer
Excitatory synapses release neurotransmitters that cause depolarisation of the postsynaptic membrane, making an action potential more likely.
5
What effect do inhibitory synapses have on the postsynaptic membrane?
Model answer
Inhibitory synapses release neurotransmitters that cause hyperpolarisation of the postsynaptic membrane, making an action potential less likely.
6
How do inhibitory neurotransmitters cause hyperpolarisation?
Model answer
Inhibitory neurotransmitters cause chloride ion channels to open, allowing Cl⁻ to enter, or potassium channels to open, allowing K⁺ to leave; both cause hyperpolarisation.

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