# A student investigates the effect of a toxin on nerve impulse transmission. The toxin blocks voltage-gated sodium ion channels in the axon membrane. Explain why the affected neurone is unable to generate an action potential after exposure to this toxin.

> OCR A-Level Biology A (H420) — 5.3 Neuronal communication · Explain · 4 marks

> Voltage-gated sodium ion channels open in response to a change in membrane potential. In a healthy neurone at rest, the membrane potential is approximately −70 mV.

## Mark scheme (4 marks)

1. Depolarisation requires sodium ions to rush into the axon
2. The membrane potential cannot become less negative / cannot reach the threshold potential
3. An action potential requires a sufficient change in membrane potential to trigger further channel opening
4. The membrane remains at / close to resting potential so no action potential is fired

## Key terms

- [voltage-gated sodium ion channels](https://www.gradenine.co.uk/glossary/voltage-gated-sodium-ion-channels)
- [action potential](https://www.gradenine.co.uk/glossary/action-potential)

## Related

- [Revision notes for OCR A-Level Biology A (H420)](https://www.gradenine.co.uk/learn)
- [How to answer "Explain" questions](https://www.gradenine.co.uk/tools/command-word-cheatsheet)
- [Practice this with AI marking (free)](https://www.gradenine.co.uk/start)

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Source: [GradeNine](https://www.gradenine.co.uk/q/a-student-investigates-the-effect-of-1707c2aa) · Published by Druglandscape Ltd.