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Saltatory conduction
 
 
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For Saltation definition, and other use disambiguation, see Saltation
Saltation

Saltation may refer to* Saltation , an evolutionary hypothesis emphasizing sudden and drastic change* Saltation , a process of particle transport by fluids....
Saltatory conduction (from the Latin saltare, to hop or leap) is a means by which action potential
Action potential

An action potential is a self-regenerating wave of electrochemical activity that allows nerve cells to carry a signal over a distance. It is the primary electrical signal generated by nerve cells, and arises from changes in the permeability of the nerve cell's axonal Cell membranes to specific ions....
s are transmitted along myelin
Myelin

Myelin is an electrically-insulating dielectric material that forms a layer, the myelin sheath. Usually, myelin surrounds only the axon of a neuron....
ated nerve fiber
Axon

An axon or nerve fiber is a long, slender projectionof a nerve cell, or neuron, that conducts action potentialaway from the neuron's cell body or soma....
s.

use the cytoplasm
Cytoplasm

The cytoplasm is the part of a Cell that is enclosed within the plasma membrane. In eukaryote cells the cytoplasm contains organelles, such as mitochondrion, that are filled with liquid kept separate from the rest of the cytoplasm by biological membranes....
 of the axon
Axon

An axon or nerve fiber is a long, slender projectionof a nerve cell, or neuron, that conducts action potentialaway from the neuron's cell body or soma....
 is electrically conductive, and because the myelin inhibits charge leakage through the membrane
Cell membrane

The cell membrane is the interface between the cellular machinery inside the cell and the fluid outside.It is a semipermeable lipid bilayer found in all cell ....
, depolarization at one node of Ranvier is sufficient to elevate the voltage at a neighboring node to the threshold for action potential initiation.






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For Saltation definition, and other use disambiguation, see Saltation
Saltation

Saltation may refer to* Saltation , an evolutionary hypothesis emphasizing sudden and drastic change* Saltation , a process of particle transport by fluids....
Saltatory conduction (from the Latin saltare, to hop or leap) is a means by which action potential
Action potential

An action potential is a self-regenerating wave of electrochemical activity that allows nerve cells to carry a signal over a distance. It is the primary electrical signal generated by nerve cells, and arises from changes in the permeability of the nerve cell's axonal Cell membranes to specific ions....
s are transmitted along myelin
Myelin

Myelin is an electrically-insulating dielectric material that forms a layer, the myelin sheath. Usually, myelin surrounds only the axon of a neuron....
ated nerve fiber
Axon

An axon or nerve fiber is a long, slender projectionof a nerve cell, or neuron, that conducts action potentialaway from the neuron's cell body or soma....
s.

Mechanism

Because the cytoplasm
Cytoplasm

The cytoplasm is the part of a Cell that is enclosed within the plasma membrane. In eukaryote cells the cytoplasm contains organelles, such as mitochondrion, that are filled with liquid kept separate from the rest of the cytoplasm by biological membranes....
 of the axon
Axon

An axon or nerve fiber is a long, slender projectionof a nerve cell, or neuron, that conducts action potentialaway from the neuron's cell body or soma....
 is electrically conductive, and because the myelin inhibits charge leakage through the membrane
Cell membrane

The cell membrane is the interface between the cellular machinery inside the cell and the fluid outside.It is a semipermeable lipid bilayer found in all cell ....
, 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
Ichiji Tasaki

Dr. Ichiji Tasaki was a Japanese biophysicist and physician involved in research relating to the electical impulses in the nervous system. He is crediting with discovering the insulating function of the myelin sheath....
 and Andrew Huxley
Andrew Huxley

Sir Andrew Fielding Huxley, Order of Merit , Royal Society is an England physiology and biophysics, who won the 1963 Nobel Prize in Physiology or Medicine for his work with Alan Lloyd Hodgkin on the basis of nerve action potentials, the electrical impulses that enable the activity of an organism to be coordinated by a central nervous system....
 and their colleagues.

Speed

The speed of the signal from one node to another is the speed of the induced electromagnetic wave, that is, the speed of light in interaction with transparent materials
Speed of light

The speed of light in an free space is an important physical constant usually written as c, with a value of 299,792,458 metres per second....
 like the cytoplasm (~100.000.000 metres per second). It should be noted, however, that any individual ion only moves with the drift velocity
Drift velocity

The drift velocity is the average velocity that a particle, such as an electron, attains due to an electric field. In general, an electron will rattle around in a conductor at the Fermi energy randomly....
, (less than a millimeter per second). It can be compared with a line of marbles pushing on each other - when poking the marble in one end then each marble only moves slightly, but this small effect on the marble in the other end is almost instantaneous, like a one-way Newton's cradle
Newton's cradle

Newton's cradle, named after Sir Isaac Newton, is a device that demonstrates conservation of momentum and conservation of energy....
. Myelinated axons serve the purpose of letting this small effect reach as far as possible before having to be enhanced again in the next node by activating ion channels anew. It is this activation of ion channels in each node of myelinated axons that makes the overall nerve signal speed being far slower than the magnitudes of the speed of light (up to ~100 metres per second). On the other hand, if there was a perfectly insulating myelin sheath, making nodes unnecessary, then it would likely transduce the signal with almost the speed of light. However, such a myelin sheath would be too large and inconvenient to be biologically efficient.

Other advantages

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.

Locations

Saltatory conduction had been found exclusively in the myelinated nerve fibers of vertebrates, but was later discovered in a pair of medial myelinated giant fibers of Penaeus orientalis (chinensie) and Penaeus japonicus , as well as a median giant fiber of an earthworm. Saltatory conduction has also been found in the small- and medium-sized myelinated fibers of Penaeus shrimp
Shrimp

Shrimp are swimming, Decapoda crustaceans classified in the infraorder Caridea, found widely around the world in both fresh water and seawater. Adult shrimp are Filter feeder benthic animals living close to the bottom....
.

See also

  • Saltation (biology)
    Saltation (biology)

    In biology, saltation is a sudden change from one generation to the next, that is large, or very large, in comparison with the usual variation of an organism....
  • Saltation (geology)
    Saltation (geology)

    In geology, saltation is a specific type of particle transport by fluids such as wind, or the denser fluid water. It occurs when loose material is removed from a bed and carried by the fluid, before being transported back to the surface....