Saltatory Conduction - Mechanism

Mechanism

Because the cytoplasm of the axon is electrically conductive, and because the myelin inhibits charge leakage through the membrane, depolarization at one node of Ranvier is sufficient to elevate the voltage at a neighboring node. Thus, the voltage at the first node of Ranvier extends spatially to the next node of Ranvier. At each successive node, the membrane potential of the axon is thereby brought to the threshold potential to initiate an action potential. Ions need only to cross the axon membrane to propagate the action potential at the nodes, but not anywhere under the myelin along the axon. Thus in myelinated axons, action potentials do not propagate continuously as waves, but instead recur at successive nodes, and in effect "hop" along the axon, by which process they travel faster than they would otherwise. (The action potential only moves in one direction, because the sodium channels at the previous node of Ranvier are inactivated, and cannot regenerate another action potential, even when depolarized.) In summary, the charge will passively depolarize the adjacent node of Ranvier to threshold, triggering an action potential in this region and subsequently depolarizing the next node, and so on. This phenomenon was discovered by Ichiji Tasaki and Andrew Huxley and their colleagues.