Inhibitory synapses at Higher Level: An AHL statement: how inhibitory neurotransmitters make an action potential less likely.
Practise this as you read
- Outline the effect of an inhibitory neurotransmitter.
- Compare excitatory and inhibitory synapses.
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The big idea: Some neurotransmitters are inhibitory. When one binds, channels open that let negative chloride ions in, so the inside of the postsynaptic neuron becomes more negative: the membrane is hyperpolarized. This is an inhibitory postsynaptic potential (IPSP), and it makes an action potential less likely.
The points to remember
- Some neurotransmitters, such as GABA, are inhibitory.
- They open channels: chloride ions (negative) enter.
- The inside becomes more negative: hyperpolarized.
- This is an IPSP: the membrane moves away from the threshold.
- An action potential in the postsynaptic neuron becomes less likely.
Remember it as: Inhibitory: more negative, further from firing.
Real example: GABA in the brain. GABA is the main inhibitory neurotransmitter in the human brain. Sleeping pills of the benzodiazepine type make GABA receptors respond more strongly, which is why they make people calm and sleepy.
Trap: Hyperpolarized means more negative, not less: an IPSP moves the membrane away from the threshold.
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How it is asked: Expect a question on what happens to the postsynaptic membrane at an inhibitory synapse, or one comparing excitatory and inhibitory synapses.
IB-style questionOutline[2 marks]
Outline the effect of an inhibitory neurotransmitter on a postsynaptic neuron.
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See the answer broken into clear points, with guidance on how each point earns marks.