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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
HL

Exam analysis

Chance of appearing4%of analysed past papers
Latest appearanceMay 2023
Most common paperPaper1
Typical marks1–2

Common command terms

  • Define
  • Outline
  • Explain
  • State
  • Label

Recent exam appearances

May 2023Paper1 ["HL"] · TZ123[ 1 ]C2.2.2—Resting potential generation
May 2022Paper2 ["HL"] · TZ13(a)[ 1 ]C2.2.2—Resting potential generation
May 2021Paper1 ["HL"] · TZ122[ 1 ]C2.2.2—Resting potential generation
May 2018Paper2 ["HL"] · TZ16(b)[ 4 ]C2.2.2—Resting potential generation
May 2018Paper3 ["HL"] · TZ26(a)[ 2 ]C2.2.2—Resting potential generation
Practice this objective

Coverage 2018–2023 · Updated 15 Jul 2026

Resting Potential Stores an Ion Gradient

A resting neuron has a stable negative membrane potential created by ion gradients and selective membrane permeability.

The sodium–potassium pump maintains high K⁺ inside and Na⁺ outside. Leak channels let more K⁺ leave than Na⁺ enter, leaving the inside relatively negative until electrical and chemical forces balance. At rest, selective ion permeability and active transport keep the membrane ready to respond to a new stimulus.

Explain resting potential with:

  • ion concentration gradients
  • selective leak permeability
  • sodium–potassium pump
  • electrical attraction opposing diffusion

If K⁺ leak channels close, the membrane potential shifts because the main outward current has changed.

The pump maintains gradients over time; it does not produce each action potential directly.

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.
ConceptIB Biology HL