Fig. 4. Schematic of flow of positive ions (sodium) during the depolarization of a myelinated axon within the optic nerve. Sodium ions flow in through voltage-gated sodium channels at the nodes of Ranvier. Repolarization occurs via the efflux of potassium at voltage-gated potassium channels in the perinodal area. The presence of myelin and the segregation of the sodium channels is responsible for saltatory conduction.