I am aware of the saltatory conduction model, nodes of Ranvier and all that, and that myelin lets electrical signals "jump". What does not add up to me entirely is what the myelin sheath insulates against, why it improves conduction through axon. If the cell membrane is already impermeable to ions, why does a "thicker membrane" improve signal conduction? There are nearly infinite memes on the internet about action potentials through axons, have not really seen any answer this though. Some vaguely mention "less leakage", but isn't the cell membrane preventing that to begin with?

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    $\begingroup$ Here's an answer I think is fit to answer your question. It gives you a better conception of how myelin does its job of insulation. $\endgroup$
    – S Pr
    Mar 2, 2020 at 15:31
  • $\begingroup$ Ions have an electrical charge which generates an electrical field that decreases in strength with distance from the ion. The cell membrane of the axon is not thick enough to stop ions on either side from being attracted to one another and interacting. The electric fields of these ions are what myelin 'insulates against'. This answer to a related question provides some good diagrams and in-depth discussion of how increasing the distance between the oppositely charged ions helps nerve function. $\endgroup$
    – timeskull
    Mar 2, 2020 at 16:26
  • $\begingroup$ @Hodgkin Can you look at the two related questions linked in comments by S Pr and timeskull? I think your question should be closed as a duplicate of one or the other. $\endgroup$
    – Bryan Krause
    Mar 2, 2020 at 16:30
  • $\begingroup$ So, myelin increases the distance to the positive ions on the outside of the axon membrane, preventing them from repelling the positive sodium ions that travel down the internodal segment by electrotonic conduction, overall decreasing resistance to sodium ion current? $\endgroup$
    – Hodgkin
    Mar 2, 2020 at 22:52
  • $\begingroup$ If that is the answer, then technically it isn't really insulating (as insulation does not insulate against electric fields?), but, just increasing distance (with non-charged matter, the myelin)? insulation in wires prevents leakage of electrons, doesn't it? isn't the metaphor, if so, misleading? $\endgroup$
    – Hodgkin
    Mar 2, 2020 at 23:01


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