Explain how inhibitory neurotransmitters can prevent a postsynaptic neuron from generating an action potential.
Written & reviewed by James Millett — Biology (Imperial College London), PGCE Science (University of Cambridge).
Model answer (4 marks)
Inhibitory neurotransmitters are released from presynaptic vesicles and bind to specific receptors on the postsynaptic membrane.
Binding causes ion channels (e.g. chloride or potassium channels) to open, producing an inhibitory postsynaptic potential (IPSP).
The membrane becomes hyperpolarised (membrane potential becomes more negative than the resting potential), moving it further from the threshold for an action potential.
Because the membrane potential does not reach the threshold, voltage‑gated sodium channels are not opened and no action potential is generated.
Binding causes ion channels (e.g. chloride or potassium channels) to open, producing an inhibitory postsynaptic potential (IPSP).
The membrane becomes hyperpolarised (membrane potential becomes more negative than the resting potential), moving it further from the threshold for an action potential.
Because the membrane potential does not reach the threshold, voltage‑gated sodium channels are not opened and no action potential is generated.
Examiner tips
- Use the term ‘inhibitory postsynaptic potential (IPSP)’. Show the sequence: release → receptor binding → ion channel opening → hyperpolarisation → no AP. Mention the specific ions (Cl⁻ or K⁺) to demonstrate depth.
- common_mistakes
- :
- Confusing excitatory with inhibitory neurotransmitters. Failing to mention hyperpolarisation or the role of voltage‑gated Na⁺ channels.
Mark scheme (4 marks)
- Inhibitory neurotransmitters are released from presynaptic vesicles and bind to specific receptors on the postsynaptic membrane.
- Binding causes ion channels (e.g. chloride or potassium channels) to open, producing an inhibitory postsynaptic potential (IPSP).
- The membrane becomes hyperpolarised (membrane potential becomes more negative than the resting potential), moving it further from the threshold for an action potential.
- Because the membrane potential does not reach the threshold, voltage-gated sodium channels are not opened and no action potential is generated.
Key terms in this question
Related
- All IB DP Biology Standard Level (2023 syllabus) revision notes →
- How to answer a "Explain" question →
- Decode the mark scheme abbreviations →
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