Propagation of action potential along myelinated nerve fiber en

neuroscience Neuroscience is the scientific study of the nervous system (the brain, spinal cord, and peripheral nervous system), its functions and disorders. It is a multidisciplinary science that combines physiology, anatomy, molecular biology, development ...

, saltatory conduction () is the propagation of

action potential An action potential occurs when the membrane potential of a specific cell location rapidly rises and falls. This depolarization then causes adjacent locations to similarly depolarize. Action potentials occur in several types of animal cells, ...

s along

myelin Myelin is a lipid-rich material that surrounds nerve cell axons (the nervous system's "wires") to insulate them and increase the rate at which electrical impulses (called action potentials) are passed along the axon. The myelinated axon can be ...

ated

axon An axon (from Greek ἄξων ''áxōn'', axis), or nerve fiber (or nerve fibre: see spelling differences), is a long, slender projection of a nerve cell, or neuron, in vertebrates, that typically conducts electrical impulses known as action po ...

s from one

node of Ranvier In neuroscience and anatomy, nodes of Ranvier ( ), also known as myelin-sheath gaps, occur along a myelinated axon where the axolemma is exposed to the extracellular space. Nodes of Ranvier are uninsulated and highly enriched in ion channels, al ...

to the next node, increasing the

conduction velocity In neuroscience, nerve conduction velocity (CV) is an important aspect of nerve conduction studies. It is the speed at which an electrochemical impulse propagates down a neural pathway. Conduction velocities are affected by a wide array of factor ...

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 Electrical resistivity (also called specific electrical resistance or volume resistivity) is a fundamental property of a material that measures how strongly it resists electric current. A low resistivity indicates a material that readily allows ...

in a simple circuit.

Mechanism

Myelinated axons only allow action potentials to occur at the unmyelinated nodes of Ranvier that occur between the myelinated internodes. It is by this restriction that saltatory conduction propagates an action potential along the axon of a

neuron A neuron, neurone, or nerve cell is an electrically excitable cell that communicates with other cells via specialized connections called synapses. The neuron is the main component of nervous tissue in all animals except sponges and placozoa. N ...

at rates significantly higher than would be possible in unmyelinated axons (150 m/s compared to 0.5 to 10 m/s). As sodium rushes into the node it creates an electrical force which pushes on the ions already inside the axon. This rapid conduction of electrical signal reaches the next node and creates another action potential, thus refreshing the signal. In this manner, saltatory conduction allows electrical nerve signals to be propagated long distances at high rates without any degradation of the signal. Although the action potential appears to jump along the axon, this phenomenon is actually just the rapid conduction of the signal inside the myelinated portion of the axon. If the entire surface of an axon were insulated, action potentials could not be regenerated along the axon resulting in signal degradation.

Energy efficiency

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.

Distribution

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 The Chinese white shrimp, oriental shrimp, or fleshy prawn (''Fenneropenaeus chinensis'') is a species of shrimp. It is cultivated at an industrial level off mainland China. Production was devastated by a series of epidemics in the 1990s and ear ...

'' and ''

Marsupenaeus japonicus ''Marsupenaeus'' is a monotypic genus of prawn. It contains a single species, ''Marsupenaeus japonicus'', known as the kuruma shrimp, kuruma prawn, or Japanese tiger prawn. It occurs naturally in bays and seas of the Indo-West Pacific, but has a ...

shrimp Shrimp are crustaceans (a form of shellfish) with elongated bodies and a primarily swimming mode of locomotion – most commonly Caridea and Dendrobranchiata of the decapod order, although some crustaceans outside of this order are refer ...

, as well as in a median giant fiber of an

earthworm An earthworm is a terrestrial invertebrate that belongs to the phylum Annelida. They exhibit a tube-within-a-tube body plan; they are externally segmented with corresponding internal segmentation; and they usually have setae on all segments. Th ...

. Saltatory conduction has also been found in the small- and medium-sized myelinated fibers of ''

Penaeus ''Penaeus'' is a genus of prawns, including the giant tiger prawn (''P. monodon''), the most important species of farmed crustacean worldwide. The genus has been reorganised following a proposition of Pérez Farfante and Kensley based on morph ...

'' shrimp.

References

External links

Saltatory conduction - Scholarpediacell biology - Why is saltatory conduction in myelinated axons faster than continuous conduction in unmyelinated axons?
{{DEFAULTSORT:Saltatory Conduction Neurophysiology de:Erregungsleitung#Saltatorische Erregungsleitung

Mechanism

Energy efficiency

Distribution

See also

References

Further reading

External links