A myelinated axon is one which is surrounded by a myelin sheath, comprised of Schwann cells . It is electrically insulating, except for gaps in the sheath which are called the Nodes of Ranvier. This insulation increases the speed of transmission of action potentials. Due to the gaps in the myelin sheath, action potentials propagate by saltatory conduction. Where action potentials jump between the nodes, there is a higher abundance of ion channels. Conduction in myelinated axons is faster than in an unmyelinated axon as the impluse 'jumps' from one Node of Ranvier to another.