Conduction Speed: Myelination and the Refractory Period · seed 1 · A4, ink-friendly. The answer key prints on its own page for grown-ups.

Jump Gaps, Set the Pace

Science · The Human Body · ages 17-18
Name ______________________   Date ____________

  1. Which two axon features speed up conduction?

    • Narrow width and bare membrane
    • Greater width and myelination
    • Short length and thin myelin

  2. Why is jumping between nodes faster than travel along bare membrane?

    • The spike only regenerates at the nodes
    • The axon grows extra nodes as it fires
    • Myelin carries the spike itself

  3. What is the absolute refractory period?

    • The rest between two separate nerves
    • The time when sodium channels are inactivated and no new spike can start
    • The pause while myelin regrows

  4. Recovery takes about 2 milliseconds. One second holds 1000 milliseconds. About how many spikes per second is that at most?

    Answer: ______________

  5. How does the refractory period set the direction of travel?

    • It speeds the spike toward the terminals
    • It pulls fresh sodium forward
    • It stops the spike re-entering exhausted membrane behind

  6. What does warming an axon do to conduction speed?

    • It slows conduction at once
    • It stops the refractory period
    • It speeds conduction until proteins cook

  7. A student says myelin speeds conduction by packing extra channels under the wrap. This claim is true.

    Circle one:   True   False

  8. Why does an impulse never travel backwards along an axon?

    • Myelin blocks both directions equally
    • The membrane behind is refractory while the membrane ahead is fresh
    • Sodium only exists ahead of the spike
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Answer key

For grown-ups. Fold this page away before handing over the rest.

Jump Gaps, Set the Pace W1-mt_x3M0sv6oD6-s1

  1. Greater width and myelination · Wider axons meet less resistance and myelin adds the jumping trick.
  2. The spike only regenerates at the nodes · Channels cluster at the nodes, so the spike leaps instead of reopening channels everywhere.
  3. The time when sodium channels are inactivated and no new spike can start · Inactivated sodium channels mean no stimulus, however strong, can fire another spike there.
  4. 500 · 1000 divided by 2 gives about 500 spikes per second at most.
  5. It stops the spike re-entering exhausted membrane behind · The patch behind is refractory while the patch ahead is fresh, so only forward travel works.
  6. It speeds conduction until proteins cook · Warmth speeds channel kinetics, but too much heat damages the proteins.
  7. False · Channels cluster at the bare nodes. The wrapped stretch carries charge passively.
  8. The membrane behind is refractory while the membrane ahead is fresh · Backward membrane cannot fire while refractory, so the spike has only one way to go.
Worksheet · LightMySky