Saltatory conduction
From Wikipedia, the free encyclopedia
Saltatory conduction (from the Latin saltare, to hop or dance) is a means by which action potentials are transmitted along myelinated nerve fibers.
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 to the threshold for action potential initiation. Thus in myelinated axons, action potentials do not propagate as waves, but recur at successive nodes and in effect "hop" along the axon, by which process they travel faster than they would otherwise. This process is outlined as the charge will passively spread to the next node of Ranvier to depolarize it to threshold which will then trigger an action potential in this region which will then passively spread to the next node and so on. This phenomenon was discovered by Ichiji Tasaki(1)(2) and Andrew Huxley (3) and their colleagues.
Apart from increasing the speed of the nerve impulse, the myelin sheath helps in reducing energy expenditure as the area of depolarization and hence the amount of sodium/potassium ions that need to be pumped to bring the concentration back to normal, is decreased.
[edit] References
1. Tasaki, I. The electro-saltatory transmission of the nerve impulse and the effect of narcosis upon the nerve fiber. Am J Physiol 127: 211-227, 1939.
2. Tasaki, I. and Takeuchi, T. Der am Ranvierschen Knoten entstehende Aktionsstrom und seine Bedeutung für die Erregungsleitung. Pflügers Arch ges Physiol. 244: 696-711, 1941.
3. Huxley AF, Stampeli R. Evidence for saltatory conduction in peripheral myelinated nerve fibres. J Physiol. 1949 May 15;108(3):315-39. PMID 16991863
