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C2.2.2—Resting potential generation

Resting potential is generated when ion pumps and membrane permeability make the inside of an axon negative relative to the outside.

Syllabus
First assessment 2025
Objective
C2.2.2
Level
SL

Exam analysis

Chance of appearing4%of analysed past papers
Latest appearanceNovember 2024
Most common paperPaper2
Typical marks1–2

Common command terms

  • Define
  • Outline
  • Explain
  • State
  • Label

Recent exam appearances

November 2024Paper2 ["SL"] · TZ25(b)[ 2 ]C2.2.2—Resting potential generation
May 2022Paper2 ["SL"] · TZ15(a)[ 1 ]C2.2.2—Resting potential generation
May 2021Paper2 ["SL"] · TZ14(b)[ 2 ]C2.2.2—Resting potential generation
May 2021Paper2 ["SL"] · TZ14(a)[ 1 ]C2.2.2—Resting potential generation
May 2018Paper3 ["SL"] · TZ24(b)(i)[ 2 ]C2.2.2—Resting potential generation
Practice this objective

Coverage 2015–2024 · Updated 15 Jul 2026

Resting Potential Stores an Ion Gradient

The resting potential is the negative voltage across a resting neuron's polarized plasma membrane, maintained by sodium and potassium ion gradients.

ATP supplies energy to the sodium–potassium pump, which moves Na⁺ out and K⁺ in opposite directions against their gradients. The membrane is more permeable to K⁺ at rest, so more positive charge diffuses out than enters and the inside remains negative relative to outside.

ATP-driven pumping establishes and maintains high Na⁺ outside and high K⁺ inside; selective leak channels create unequal ion movement; separated charge produces membrane polarization and a measurable membrane potential.

If ATP production stops, the pump can no longer maintain the gradients. Existing gradients may persist briefly, but continued leakage gradually erodes the negative resting potential.

The pump maintains the gradients over time; it does not directly create each action potential. A concentration gradient and a voltage gradient both influence ion movement.

Resting potential generation

Assessment in practice

1–2 marks
How it is assessed

This objective is assessed through structured response, commonly using Define / Outline / Explain.

Command terms

Define / Outline / Explain / State / Label

What earns marks

Build the answer around this relationship: The resting axon is negative inside relative to outside.

Representative question

Question 1

[Maximum number: 4]

Outline how neurons generate a resting potential.

SL Transfer: Explain Core Neural Signalling

Neurons carry electrical impulses in the nervous system; motor, sensory, and relay neurons differ in axon, dendrite, and cell body arrangement. Sodium-potassium pumps use ATP to move 3 Na+ out and 2 K+ in; ion gradients make the resting axon polarized at about -70 mV. A nerve impulse is a propagated action potential along a nerve fibre; stimulus-triggered sodium influx reverses membrane polarity. Larger axon diameter lowers resistance and increases impulse speed; myelin sheaths and nodes of Ranvier enable faster saltatory conduction. Synapses connect neurons to neurons, muscles, or glands; chemical synapses transmit one way across a narrow synaptic cleft. Action potentials open voltage-gated Ca2+ channels in presynaptic terminals; Ca2+ causes vesicle fusion and neurotransmitter exocytosis into the cleft. Neurotransmitters diffuse and bind receptors on the postsynaptic membrane; EPSPs depolarize the membrane and make threshold more likely.

Concept essentials

  • The resting axon is negative inside relative to outside.
  • The sodium-potassium pump uses ATP to maintain ion gradients.
  • Three sodium ions are pumped out for every two potassium ions pumped in.
  • Resting potential is an actively maintained state, not an absence of membrane processes.