Myelinated axon

Why myelinated axon have a high conduction velocity?
Answer: This is the result of a very large increase in length constant and a decrease in propagation time constant caused by the wrapping of fatty, insulating myelin around the fiber. This dramatically increases the membrane resistance (Rm) in the myelinated region because the current has to pass across the myelin sheath as well as the axon plasma membrane. In addition, the membrane capacitance (Cm) is reduced by myelination: the thicker insulation result in less charge separation per unit membrane area.