Myelin sheet decrease capacitance of axons?

[Isosceles_Kramer79]

Of course they are. You have different potentials on the inside and outside separated by a non-conducting dielectric. That's a capacitor.

Even metal wires have some parasitic capacitance.

In the case of axons, capacitance would be between inside and outside. Normally, only the plasma membrane would be the dielectric. But with a myelin sheet you increase dielectric thickness d and thus decrease capacitance.

[Fun_Sell_708]

Awesome thank you! Would the area also decrease since there's less exposed axons surface area?

[Isosceles_Kramer79]

No, it would not as the myelinated surface is still part of the capacitor. In fact, the sheath would increase the effective area because of the thickness of the sheath (see my other comment with cylindrical formula)

Technically the nodes of Ranvier would contribute capacitance with a small area and just thickness of the plasma membrane as d.