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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:
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".
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?