How does myelination of neurones increase conduction velocity?

Myelination is the production of a myelin sheath - a fatty, electrically insulating layer formed by Schwann cells wrapping around the axons of neurons. This sheath is not continuous, there are gaps between Schwann cells which are called nodes of Ranvier. At these nodes, the axon membrane (containing sodium and potassium ion channels) is uncovered/exposed to ions in extracellular solution. Therefore depolarisation can only occur at the nodes of Ranvier. Since the action potential jumps from node to node (this is called saltatory conduction), the action potential travels a greater distance for a shorter period of time. In an unmyelinated axon, every single section of the membrane will have to be depolarised for the impulse to conduct along the axon, hence taking more time.