# Explain why a neurone cannot be stimulated to produce a second action potential immediately after the first action potential has occurred.

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

> During a nerve impulse, ion movements across the axon membrane produce rapid changes in membrane potential. Immediately after an action potential, the neurone enters a refractory period during which it is unresponsive to further stimulation.

## Mark scheme (4 marks)

1. Voltage-gated sodium ion channels are inactivated / closed and cannot be reopened immediately after depolarisation
2. The membrane is hyperpolarised / the membrane potential is more negative than the resting potential during the refractory period
3. Voltage-gated potassium ion channels remain open, causing continued outward movement of K⁺ ions
4. A sufficiently large stimulus cannot generate a new depolarisation / threshold cannot be reached until the resting potential is restored

## Key terms

- [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)

---
Source: [GradeNine](https://www.gradenine.co.uk/q/explain-why-a-neurone-cannot-be-e78b8e2d) · Published by Druglandscape Ltd.