Final answer:
The myelin sheath insulates the axon, increasing the speed of action potential conduction through saltatory conduction.
Step-by-step explanation:
The myelin sheath acts as an insulator on the axon, preventing current from leaving the axon and increasing the speed of action potential conduction. When an action potential reaches a node of Ranvier, the voltage-gated Na+ channels in the node allow the ions to flow across the membrane, regenerating the action potential. This jumping of the action potential from one node to the next is called saltatory conduction. If the axon did not have myelin sheaths and nodes of Ranvier, the action potential would propagate much more slowly.