Why does a myelination cause an action potential to travel faster down the axon?
In order to understand why myelination improves the conduction of an action potential down the length of axon, you have to make sure you understand how propagation occurs. When you have a depolarizing stimulus at the axon hillock, Na+ channels open and allow and influx of Na+ into the cell. This influx causes a deploarization of the membrane adjacent to the axon hillock, and causes the opening of Na+ channels there. This process continues all the way down to the axon terminal. Now, in both unmyelinated and myelinated cells, Na/K ATPases are present along with Na+ and K+ channels, along the length of axon. If a cell is unmyelinated, it can pump Na+ back out into the ECF, causing a loss of conduction and decreasing the frequency of axon potentials. In myelinated cells, however, the myelin blocks these pumps from pumping Na+ out of the cell, and maintains concentrations. If Na/K ATPases are only able to pump Na+ ions out at the nodes of Ranvier, leakage will only occur there.
