--- title: "The Resting Potential and the Action Potential" description: "A neurone's resting voltage depends mainly on ion gradients and its greater permeability to potassium. An ATP-driven pump maintains the gradients. During an action potential, voltage-gated sodium and " canonical: https://lightmysky.com/learn/science/the-resting-potential-and-the-action-potential-mt_0sh4w30ocz source: https://lightmysky.com/learn/science/the-resting-potential-and-the-action-potential-mt_0sh4w30ocz.md retrieved: 2026-11-12 --- > **Agent view.** This is the Markdown twin of the page, for tools and assistants. > When to use this site, and the call that answers each job: https://lightmysky.com/agent-instructions.md > API description (OpenAPI 3.1): https://lightmysky.com/openapi.json · Authentication: https://lightmysky.com/auth.md > Pricing: https://lightmysky.com/pricing.md · Catalog: https://lightmysky.com/llms.txt · Full catalog: https://lightmysky.com/llms-full.txt > Every machine-readable file on this domain: https://lightmysky.com/.well-known/ai-catalog.json > Ask for Markdown with `Accept: text/markdown`, a `.md` address, or `?mode=agent`. # The Resting Potential and the Action Potential A neurone's resting voltage depends mainly on ion gradients and its greater permeability to potassium. An ATP-driven pump maintains the gradients. During an action potential, voltage-gated sodium and potassium channels change the voltage in sequence. Subject: Science · Area: The Human Body · Ages 17 to 18 Page: https://lightmysky.com/learn/science/the-resting-potential-and-the-action-potential-mt_0sh4w30ocz ## Ready when they can - Explains what maintains the resting potential and what it costs the cell. - Orders depolarisation, repolarisation and hyperpolarisation and matches them to the rise, fall and dip below resting voltage. - Says which ion moves at each stage and through which kind of channel. ## Lesson: The spark that travels the nerve A typical neurone rests near minus 70 millivolts (mV), measured inside relative to outside. Values vary. The membrane is more permeable to potassium than sodium. Some potassium leaves through leak channels, separating charge and making the inside negative. The resulting voltage opposes further potassium loss. This permeability, together with ion gradients, is the main basis of the resting potential. As in co-transport, the sodium potassium pump maintains ion gradients. It uses one ATP per cycle to move three sodium ions out and two potassium ions in. The pump also contributes directly to voltage, but mainly supports resting voltage by maintaining gradients. Blocking it does not erase existing gradients at once. Continued ion movement weakens them over time, so resting voltage tends to become less negative. If depolarisation reaches threshold, an action potential begins. Voltage-gated sodium channels open rapidly. Sodium enters and voltage rises: depolarisation. Sodium channels then inactivate while slower voltage-gated potassium channels open. Potassium leaves and voltage falls: repolarisation. Continued potassium outflow can briefly take voltage below the resting level: hyperpolarisation. *(drawing: On a voltage trace: rise, fall, dip below resting, then return. These boxes show order, not a scaled voltage graph.)* The dip occurs because voltage-gated potassium channels close slowly, allowing potassium to keep leaving briefly. As these channels close, the usual resting ion conductances bring voltage back toward rest. The pump maintains concentrations over time; it does not directly cause the rapid fall or end the dip. A typical spike lasts a few milliseconds, though timing varies. An impulse normally travels along an axon as local electrical current brings the next region to threshold. Voltage-gated sodium channels there open and generate another action potential. Just behind it, recently used sodium channels are temporarily inactivated. This refractory region cannot immediately fire again, limiting backward re-excitation. The pump keeps maintaining gradients throughout. Small local voltage changes can fade with distance. Reaching threshold triggers a full, all-or-nothing spike. Under the same conditions, a stronger stimulus does not produce a proportionally larger spike. Chemical synapses can start local changes through neurotransmitter-gated channels; sensory signals can start through other channels. Myelin, axon diameter and the distribution of voltage-gated channels affect conduction speed. **Recap.** The pump maintains ion gradients. Potassium permeability mainly shapes resting voltage. Sodium entry drives the spike's rise; potassium exit drives its fall and brief dip. *Lesson, questions and flashcards written for this dataset.* ## Practice 8 questions on this page, each with its working shown. ## Needs first - [The Reflex Arc and Synapses](https://lightmysky.com/learn/science/the-reflex-arc-and-synapses-mt_evlgCVxTnK) - [Co-transport and Coupled Movement Across Membranes](https://lightmysky.com/learn/science/co-transport-and-coupled-movement-across-membranes-mt_pzQ8n3FWNV) ## Opens up - [Equilibrium potentials and what sets the resting voltage](https://lightmysky.com/learn/science/equilibrium-potentials-and-what-sets-the-resting-voltage-mt_mRT_5vDEO1) - [Conduction Speed: Myelination and the Refractory Period](https://lightmysky.com/learn/science/conduction-speed-myelination-and-the-refractory-period-mt_x3M0sv6oD6)