Neural Control and Coordination

Biology · Class 11

Simulation · Biology · Class 11

A wave along the axon

"A wave along the axon" is a free, interactive Class 11 Biology simulation for NEET, built on the lesson "Nerve impulse" in Neural Control and Coordination. Step time forward and watch the charges on each side of the membrane. Look for where Na⁺ enters, where K⁺ leaves, and which way the little currents run. Then turn the stimulus off. Stimulus → Na⁺ rushes in → polarity reverses (action potential) → local currents depolarise the next site → K⁺ diffuses out and restores the resting potential. The impulse is a travelling wave of depolarisation and repolarisation.

From the lesson Nerve impulse in Neural Control and Coordination. Change the values and watch what happens.

A wave along the axonBiology · Class 11

The idea behind it

NCERT §18.3.1

  • When a stimulus hits a site on the polarised membrane (site A), the membrane there becomes freely permeable to Na⁺.
  • Na⁺ rushes in, and the polarity at that site reverses: the outer surface turns negative and the inner surface positive. The site is depolarised.
  • The potential difference across the membrane at site A is the action potential; this is the nerve impulse.
  • Just ahead, at site B, the membrane is still positive outside and negative inside. So current flows along the inner surface from A to B, and along the outer surface from B to A, completing the circuit.
  • This reverses the polarity at B and an action potential forms there: the impulse has moved from A to B. Repeated along the axon, the impulse is conducted.
  • The rise in Na⁺ permeability lasts only a very short time. It is quickly followed by a rise in K⁺ permeability; within a fraction of a second K⁺ diffuses out, restoring the resting potential at the site, which can then respond to a new stimulus.
  • The impulse is thus a wave of depolarisation followed by repolarisation travelling along the axon membrane.

Questions

2 answers

What does the "A wave along the axon" simulation show?
Step time forward and watch the charges on each side of the membrane. Look for where Na⁺ enters, where K⁺ leaves, and which way the little currents run. Then turn the stimulus off.
Is this simulation free?
Yes. It is free and runs in the browser on a phone or a laptop. It belongs to the lesson "Nerve impulse" in Neural Control and Coordination (Class 11 Biology).

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