Resting Potential
Laura Armstrong & Joe Wolfensohn
Teachers
Contents
Recall Questions
This topic requires prior knowledge of movement across cell membranes. You can test your knowledge on this below.
What is active transport?
The movement of molecules or ions against a concentration gradient, using energy from ATP.
What is diffusion?
The net movement of particles from a region of high concentration to low concentration, down a concentration gradient. Diffusion is passive.
Why can ions not diffuse through the phospholipid bilayer of a cell membrane?
They are charged and so require a transport protein such as a channel protein for facilitated diffusion.
Topic Explainer Video
Check out this @JoeDoesBiology video that explains resting potential in leaves or read the full notes below. Once you've gone through the whole note, try out the practice questions!
What Is the Resting Potential?
- A resting potential is the potential difference across the axon membrane of a neurone when it is not transmitting an electrical impulse (aka an action potential).
- The inside of the axon is negatively charged compared to the outside.
- The resting potential is typically around –70 mV.
How Is the Resting Potential Maintained?
Maintained by:
1. Sodium–Potassium Pump (Active Transport)
- Pumps 3 Na⁺ out of the axon and 2 K⁺ in to the axon.
- Uses ATP to move ions against their concentration gradients.
- Results in more positive ions outside the membrane than inside.
2. Membrane Permeability to Ions
- Membrane is more permeable to K⁺ than to Na⁺.
- Potassium ions diffuse out via K⁺ channels (this is facilitated diffusion).
- Very few Na⁺ diffuse back in, maintaining a net negative charge inside the axon and a more positive charge outside of the axon.
3. Overall Effect
- More positive ions move out than in.
- Inside of axon becomes electronegative relative to the outside.
- This creates and maintains the resting potential of –70 mV.
- We say the neurone membrane is polarised when it is at rest.
Summary Table
| Feature | Description |
| Resting Potential Value | –70 mV. |
| Na⁺/K⁺ Pump Action | 3 Na⁺ out, 2 K⁺ in. |
| Membrane Permeability | More Permeable to K⁺ than Na⁺. |
| Ion Movement by Diffusion | K⁺ diffuses out, little Na⁺ diffuses in. |
| Energy Requirement | The Sodium Potassium pump requires ATP (for Active Transport of Ions). |
| Net Result | Inside of Axon is negatively charged relative to the outside. |
Key Terms
- Resting potential: The potential difference across the axon membrane when the neurone is not stimulated.
- Sodium–potassium pump: A carrier protein that uses ATP to actively transport 3 Na⁺ out and 2 K⁺ into the axon.
- K⁺ channels: Protein channels that allow potassium ions to move out of the axon down their concentration gradient.
- Polarised: Describes a neurone membrane with a potential difference across it (e.g., resting state).
No answer provided.
Exam Tips
Don’t confuse diffusion and active transport.
Na⁺ and K⁺ move by active transport via the sodium-potassium pump.
K⁺ also diffuses out passively.
The membrane is less permeable to Na⁺ so few Na⁺ diffuse back in to the neurone.
Make sure you are saying ‘potassium ions’ and ‘sodium ions’, or using the correct chemical symbols, and not just talking about sodium and potassium!
No answer provided.
Describe how the resting potential is established and maintained in a neurone. (3 marks)
- Sodium ions actively transported out and potassium ions actively transported in. Accept 3 Na⁺ out and 2 K⁺ in but reject if numbers used are incorrect.
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potassium ions diffuse back out OR sodium ions can’t diffuse back in.
- Membrane more permeable to potassium ions OR Membrane less permeable to sodium ions.
Practice Question 1
Try to answer the practice question from the TikTok on your own, then watch the video to see how well you did!
Practice Question 2
If you want to try out another one, check this video out and see how you do!