Saltatory conduction

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For the definition of saltation, see Saltation (biology).
Structure of a typical neuron
Saltatory conduction occurs only on myelinated axons.

Saltatory conduction (from the Latin saltare, to hop or leap) is the propagation of action potentials along myelinated axons from one node of Ranvier to the next node, increasing the conduction velocity of action potentials. The uninsulated nodes of Ranvier are the only places along the axon where ions are exchanged across the axon membrane, regenerating the action potential between regions of the axon that are insulated by myelin, unlike electrical conduction in a simple circuit.

Mechanism[edit]

In order for an action potential to travel along the axon of a nerve cell, a spike-like voltage change must occur across the axon membrane. Regeneration of action potentials must be repeated many times along the axon by ion channel molecules.[1] However, with myelin sheaths insulating the axon, an action potential can "jump" from one region of the axon membrane where ion channels are present to the next – from one node of Ranvier to another. In this way, the signal travels faster by skipping across the insulated sections. The action potential moves only in one direction, because the sodium channels at the previous node of Ranvier are inactivated and cannot regenerate another action potential even when depolarized. The charge passively depolarizes the next 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[2][3] and Andrew Huxley[4] and their colleagues.

Energy efficiency[edit]

In addition to increasing the speed of the nerve impulse, the myelin sheath helps in reducing energy expenditure over the axon membrane as a whole, because the amount of sodium and potassium ions that need to be pumped to bring the concentrations back to the resting state following each action potential is decreased.[1]

Distribution[edit]

Saltatory conduction occurs widely in the myelinated nerve fibers of vertebrates, but was later discovered in a pair of medial myelinated giant fibers of Fenneropenaeus chinensis and Marsupenaeus japonicus shrimp,[5][6][7] as well as in a median giant fiber of an earthworm.[8] Saltatory conduction has also been found in the small- and medium-sized myelinated fibers of Penaeus shrimp.[9]

See also[edit]

References[edit]

  1. ^ a b Tamarkin, Dawn. "Saltatory Conduction of APs". Retrieved 6 May 2014. 
  2. ^ 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
  3. ^ 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
  4. ^ Huxley AF, Stämpfli R. Evidence for saltatory conduction in peripheral myelinated nerve fibres. J Physiol. 108:315–39, 1949. PMID 16991863
  5. ^ Hsu K, Tan TP, Chen FS. On the excitation and saltatory conduction in the giant fiber of shrimp (Penaeus orientalis). Proceedings of the 14th National Congress of the Chinese Association for Physiological Sciences. 1964, Aug. 7–15, Dalian, p. 17
  6. ^ Hsu K, Tan TP, Chen FS. Saltatory conduction in the myelinated giant fiber of shrimp (Penaeus orientalis). KexueTongbao 20:380–382, 1975
  7. ^ Kusano K, La Vail MM. Impulse conduction in the shrimp medullated giant fiber with special reference to the structure of functionally excitable areas. J Comp Neurol. 142:481–494, 1971
  8. ^ Gunther J. Impulse conduction in the myelinated giant fibers of the earthworm. Structure and function of the dorsal nodes in the median giant fiber. J Comp Neurol. 168:505–531, 1976
  9. ^ Xu (Hsu) K, Terakawa S. Saltatory conduction and a novel type of excitable fenestra in shrimp myelinated nerve fibers. Jap J Physiol. 43 (suppl. 1), S285–S293

External links[edit]