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One usually reads that the functional role of the myelin sheath is being a good insulator, accelerating the speed of action potential propagation along the myelinated axon.

I tried to understand this and came up with these possibilities:

  1. The immediate reason why action potential propagation along myelinated axons is "faster than normal" is a relative lack of leak channels in the membrane. I.e. it is the membrane of the neuron (not the myelin sheath itself) that is a "better insulator than normal".
    Why there are no leak channels underneath the myelin sheath would be another question. But the myelin sheath would probably be one of the reasons. Thus, it would be an insulator only "indirectly".

  2. Or there are leak channels, but there's no place to go for the ions out of the neuron (no extracellular fluid to diffuse to)?
    In this case, it would be the myelin sheath that is the "immediate" insulator. But the leak channels would be useless. (So why to maintain them?)

So my question is:

Are there significantly less leak channels underneath the myelin sheath than normal, or not?

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marked as duplicate by theforestecologist, Community Dec 8 '17 at 11:46

This question has been asked before and already has an answer. If those answers do not fully address your question, please ask a new question.

  • $\begingroup$ The myelin itself is an insulator. It wouldn't matter if there are leak channels under the myelin sheath or not: they are covered by a thick, fatty, non-conductive layer of folded membranes. Your title "Functional role of the myelin sheath" is not really related to the question you ask "Are there significantly less leak channels underneath the myelin sheath than normal, or not?" The answer to the second question has nothing to do with the function of the myelin sheath, the question would be whether cells have trafficking mechanisms to keep leak channels out of places where they are useless. $\endgroup$ – Bryan Krause Dec 7 '17 at 20:10
  • $\begingroup$ I disagree with your last sentence, starting with "the answer to the second question": The myelin sheath itself might be a cause and part of a trafficking mechanism to keep leak channels out of place... and so has possibly to do with it. $\endgroup$ – Hans-Peter Stricker Dec 8 '17 at 0:47
  • $\begingroup$ @BryanKrause: You say "it wouldn't matter if there are leak channels under the myelin sheath or not". I claim: it does, because it is expensive. (It would be cheaper not to have them, without loss of functionality.) $\endgroup$ – Hans-Peter Stricker Dec 8 '17 at 1:02
  • $\begingroup$ "I claim: it does, because it is expensive" - exactly, but then we aren't talking about the function of the myelin sheath anymore, which was the title of your question. Do you want to ask about function of myelin? If so, the presence of leak channels under the myelin is irrelevant. Do you want to talk about efficiency? If so, then the function of myelin is irrelevant. $\endgroup$ – Bryan Krause Dec 8 '17 at 1:52
  • $\begingroup$ This is already answered here $\endgroup$ – theforestecologist Dec 8 '17 at 4:22