--- title: "Conduction Speed: Myelination and the Refractory Period" description: "Myelin speeds conduction by reducing current leak and allowing action potentials to regenerate at nodes. Refractory periods limit firing frequency and prevent recently active membrane from immediately" canonical: https://lightmysky.com/learn/science/conduction-speed-myelination-and-the-refractory-period-mt_x3M0sv6oD6 source: https://lightmysky.com/learn/science/conduction-speed-myelination-and-the-refractory-period-mt_x3M0sv6oD6.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`. # Conduction Speed: Myelination and the Refractory Period Myelin speeds conduction by reducing current leak and allowing action potentials to regenerate at nodes. Refractory periods limit firing frequency and prevent recently active membrane from immediately firing again. Subject: Science · Area: The Human Body · Ages 17 to 18 Page: https://lightmysky.com/learn/science/conduction-speed-myelination-and-the-refractory-period-mt_x3M0sv6oD6 ## Ready when they can - Explains how myelin speeds passive current spread and where action potentials regenerate. - Explains how axon diameter and temperature can affect conduction speed. - Links refractory periods to impulse direction and maximum firing frequency. ## Lesson: Jump Gaps, Set the Pace Myelin insulates an axon between gaps called nodes of Ranvier. It reduces current leak and lowers membrane capacitance, so less charge is needed to change membrane voltage. Current spreads passively between nodes. Voltage-gated sodium channels are concentrated at nodes, where action potentials regenerate. This is saltatory conduction. Without myelin, successive membrane regions regenerate the signal. *(drawing: This shows the order of signal regeneration, not axon anatomy. Current spreads between nodes; the action potential regenerates at each node.)* Greater axon diameter lowers internal resistance to current, usually speeding conduction when other conditions match. Moderate warming within a healthy axon's physiological range usually speeds channel gating and conduction. Excess heat can impair function, so this is not an unlimited warming rule. Myelin loss increases current leak and can slow or block conduction. The absolute refractory period begins during a spike. Many sodium channels are inactivated, so another spike cannot start in that membrane region, even with a strong stimulus. During the following relative refractory period, a stronger stimulus can trigger another spike. Sodium channels are recovering, while continued potassium conductance and hyperpolarisation can keep excitability below normal. **Example.** A normal spike travels from its initiation region toward the terminals. Current spreads both ways, but recently active membrane behind it is refractory and cannot immediately fire again. Resting membrane ahead can respond. Direction is not a permanent property of the axon: stimulating the middle of an axon that is resting throughout can launch spikes in both directions. *(drawing: Absolute: another spike cannot start. Relative: a stronger stimulus can trigger one. The cells do not represent equal durations.)* **Example.** For a theoretical maximum firing rate, divide 1000 milliseconds by the minimum interval between spike starts. If the interval is 4 milliseconds, 1000 / 4 = 250 spikes per second. Absolute refractoriness sets an upper limit. Relative refractoriness and other cell properties can lower the actual rate. The interval differs among neurones. **Recap.** Myelin speeds current spread between nodes. Diameter and temperature affect speed. Refractory periods limit firing rate and prevent immediate re-excitation of recently active membrane. *Lesson, questions and flashcards written for this dataset. Factual background includes OpenStax chapters on action potentials and neuronal communication.* ## Practice 8 questions on this page, each with its working shown. ## Needs first - [The Resting Potential and the Action Potential](https://lightmysky.com/learn/science/the-resting-potential-and-the-action-potential-mt_0sh4w30ocz) ## Opens up - [Synaptic Transmission, Summation and Inhibition](https://lightmysky.com/learn/science/synaptic-transmission-summation-and-inhibition-mt_0uM8xRV92B) - [Cable Properties and Dendritic Integration](https://lightmysky.com/learn/science/cable-properties-and-dendritic-integration-mt_bbPl-eJUFF)