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?