Saltatory conduction - AbsoluteAstronomy.com

For Saltation definition, see 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...

Saltatory conduction (from the Latin saltare, to hop or leap) is the propagation of action potential

Action potential

In physiology, an action potential is a short-lasting event in which the electrical membrane potential of a cell rapidly rises and falls, following a consistent trajectory. Action potentials occur in several types of animal cells, called excitable cells, which include neurons, muscle cells, and...

s along myelin

Myelin

Myelin is a dielectric material that forms a layer, the myelin sheath, usually around only the axon of a neuron. It is essential for the proper functioning of the nervous system. Myelin is an outgrowth of a type of glial cell. The production of the myelin sheath is called myelination...

ated axon

Axon

An axon is a long, slender projection of a nerve cell, or neuron, that conducts electrical impulses away from the neuron's cell body or soma....

s from one node of Ranvier to the next node, increasing the conduction velocity of action potentials without needing to increase the diameter of an axon.

Mechanism

Because the cytoplasm

Cytoplasm

The cytoplasm is a small gel-like substance residing between the cell membrane holding all the cell's internal sub-structures , except for the nucleus. All the contents of the cells of prokaryote organisms are contained within the cytoplasm...

of the axon

Axon

An axon is a long, slender projection of a nerve cell, or neuron, that conducts electrical impulses away 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 or plasma membrane is a biological membrane that separates the interior of all cells from the outside environment. The cell membrane is selectively permeable to ions and organic molecules and controls the movement of substances in and out of cells. It basically protects the cell...

, depolarization

Depolarization

In biology, depolarization is a change in a cell's membrane potential, making it more positive, or less negative. In neurons and some other cells, a large enough depolarization may result in an action potential...

at one node of Ranvier is sufficient to elevate the voltage

Voltage

Voltage, otherwise known as electrical potential difference or electric tension is the difference in electric potential between two points — or the difference in electric potential energy per unit charge between two points...

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

Membrane potential

Membrane potential is the difference in electrical potential between the interior and exterior of a biological cell. All animal cells are surrounded by a plasma membrane composed of a lipid bilayer with a variety of types of proteins embedded in it...

of the axon is thereby brought to the threshold potential

Threshold potential

The threshold potential is the membrane potential to which a membrane must be depolarized to initiate an action potential.It often can be between −40 and -55 mV, but it can vary based upon several factors...

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

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 credited with discovering the insulating function of the myelin sheath...

and Andrew Huxley

Andrew Huxley

Sir Andrew Fielding Huxley, OM, FRS is an English physiologist and biophysicist, who won the 1963 Nobel Prize in Physiology or Medicine for his experimental and mathematical work with Sir Alan Lloyd Hodgkin on the basis of nerve action potentials, the electrical impulses that enable the activity...

and their colleagues.

Energy efficiency

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.

Distribution

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, decapod crustaceans classified in the infraorder Caridea, found widely around the world in both fresh and salt water. Adult shrimp are filter feeding benthic animals living close to the bottom. They can live in schools and can swim rapidly backwards. Shrimp are an important...

Mechanism

Energy efficiency

Distribution

See also