Conduction of impulse, Biology



  • The impulse moves along the axon as local effect by altering the permeability of neighbouring Na+  channels and affecting every next channels in succession moving the effect ahead from axon hilllock to the axon terminal.
  • This is called stepwise or local circuit theory of transmission & is comparatively a slower conduction, generally found in invertebrates.


  • As axon is insulated the impulse, generated at axon hilock can effect the Na+  channel only at the node of Ranvier where the axolemma is exposed, which means Na+  can cross the membrane only at these sites.
  • This effect moves quickly from one node to another i.e. saltatory transmission.
  • Velocity of transmission of impulse is a to       

                     - degree of myelination

                     - temperature

                     - diameter of axon, it is 1500 m in sea squid while in vertebrats only 25-35 m

  • The average valocity of conduction in frog is about 20-25 m/sec. while in mammals 100-200 m/sec.
  • The fastest in some nerves of human beings is upto 532 kmph.

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Posted Date: 10/3/2012 2:25:34 AM | Location : United States

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