Due to the myelination of neurones within mammalian nervous systems, action potentials may only occur at the Nodes of Ranvier. Myelin is made up of insulating cells which means depolarisation cannot occur in myelinated regions. Between these cells however, there are gaps known as the Nodes of Ranvier which are unmyelinated. As depolarisation cannot occur at the cells making up the myelin sheath, the wave of depolarisation can only occur at the Nodes of Ranvier. Thus, action potentials appear to jump from node to node when travelling down an axon.
Not only does saltatory conduction increase the speed of impulse transmission by causing the depolarization process to jump from one node to the next, it also conserves energy for the axon as depolarization only occurs at the nodes and not along the whole length of the nerve fibre, as in unmyelinated fibres. This leads to up to 100 times less movement of ions than would otherwise be necessary, therefore conserving the energy required to re-establish the Na+ and K+ concentration differences across the membranes following a series of action potentials being propogated along the fibre.