# Explain how the resting membrane potential of a neuron is established and maintained.

> IB DP Biology Standard Level (2023 syllabus) — C2.2 Neural signalling · Explain · 4 marks

## Mark scheme (4 marks)

1. The resting membrane potential is approximately −70 mV (inside negative relative to outside).
2. The sodium–potassium pump (Na⁺/K⁺-ATPase) actively transports 3 Na⁺ out of the cell for every 2 K⁺ pumped in, using ATP, creating a net export of positive charge.
3. The membrane is much more permeable to K⁺ than to Na⁺ at rest (via leak channels), so K⁺ diffuses out down its concentration gradient, leaving behind negatively charged organic anions.
4. An electrochemical equilibrium is reached for K⁺ when the electrical attraction pulling K⁺ back in balances its outward concentration gradient, stabilising the membrane potential.

## Key terms

- [resting membrane potential](https://www.gradenine.co.uk/glossary/resting-membrane-potential)

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Source: [GradeNine](https://www.gradenine.co.uk/q/explain-how-the-resting-membrane-potential-d2c3824c) · Published by Druglandscape Ltd.