Editing Saltatory conduction

{{short description|Propagation of action potentials along the myelinated axons of neurons}}
{{For|the definition of saltation in evolutionary biology|Saltation (biology)}}
[[File:Saltatory Conduction.gif|thumb|Action potential propagation in myelinated [[neuron]]s is faster than in unmyelinated neurons because of saltatory conduction.]]
{{Neuron map|Saltatory conduction occurs only on [[myelin]]ated [[axons]].}}
[[File:Propagation of action potential along myelinated nerve fiber en.svg|thumb|400px|Propagation of [[action potential]] along [[myelin]]ated nerve fiber]]

In [[neuroscience]], '''saltatory conduction''' ({{etymology|la|{{wikt-lang|la|saltus}}|leap, jump}}) is the propagation of [[action potential]]s along [[myelin]]ated [[axon]]s from one [[node of Ranvier]] to the next, 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 conductor|electrical conduction]] 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]] at rates significantly higher than would be possible in unmyelinated axons (150&nbsp;m/s compared from 0.5 to 10&nbsp;m/s).<ref>{{cite book | vauthors = Purves D, Augustine GJ, Fitzpatrick D | chapter = Increased Conduction Velocity as a Result of Myelination | chapter-url = https://www.ncbi.nlm.nih.gov/books/NBK10921/ | title = Neuroscience | edition = 2nd | location = Sunderland (MA) | publisher = Sinauer Associates | year = 2001 }}</ref> 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 way, electrical nerve signals can propagate rapidly, over long distances, without degradation.{{Cn|date=January 2025}} 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.{{cn|date=May 2024}} In the [[Central nervous system|CNS]], nerve cells have been shown to individually alter the size of the nodes to tune conduction speeds.<ref>{{cite journal | last=Arancibia-Cárcamo | first=I Lorena | last2=Ford | first2=Marc C | last3=Cossell | first3=Lee | last4=Ishida | first4=Kinji | last5=Tohyama | first5=Koujiro | last6=Attwell | first6=David | title=Node of Ranvier length as a potential regulator of myelinated axon conduction speed | journal=eLife | volume=6 | date=2017-01-28 | issn=2050-084X | pmid=28130923 | pmc=5313058 | doi=10.7554/eLife.23329 | doi-access=free }}</ref>

==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 [[Ion transporter|pumped]] to bring the concentrations back to the resting state following each action potential is decreased.<ref name="AP">{{cite web|last=Tamarkin|first=Dawn | name-list-style = vanc |title=Saltatory Conduction of APs|url=http://faculty.stcc.edu/AandP/AP/AP1pages/nervssys/unit11/saltator.htm|access-date=6 May 2014|url-status=dead|archive-url=https://web.archive.org/web/20141030102403/http://faculty.stcc.edu/AandP/AP/AP1pages/nervssys/unit11/saltator.htm|archive-date=30 October 2014}}</ref>

==Distribution==

Saltatory conduction occurs widely in the myelinated nerve fibers of vertebrates, but was later discovered in a pair of medial myelinated [[Ventral nerve cord|giant fiber]]s of ''[[Fenneropenaeus chinensis]]'' and ''[[Marsupenaeus japonicus]]'' [[shrimp]],<ref>{{cite journal | vauthors = Hsu K, Tan TP, Chen FS | title = On the excitation and saltatory conduction in the giant fiber of shrimp (''Penaeus orientalis''). | journal = Proceedings of the 14th National Congress of the Chinese Association for Physiological Science | date = August 1964 | pages = 7–15 }}</ref><ref>{{cite journal | vauthors = Hsu K, Tan TP, Chen FS | title = Saltatory conduction in the myelinated giant fiber of shrimp (''Penaeus orientalis''). | journal = KexueTongbao | volume = 20 | pages = 380–382 | date = 1975 }}</ref><ref>{{cite journal | vauthors = Kusano K, LaVail MM | title = Impulse conduction in the shrimp medullated giant fiber with special reference to the structure of functionally excitable areas | journal = The Journal of Comparative Neurology | volume = 142 | issue = 4 | pages = 481–94 | date = August 1971 | pmid = 5111883 | doi = 10.1002/cne.901420406 | s2cid = 33273673 }}</ref> as well as in a median giant fiber of an [[earthworm]].<ref>{{cite journal | vauthors = Günther J | title = Impulse conduction in the myelinated giant fibers of the earthworm. Structure and function of the dorsal nodes in the median giant fiber | journal = The Journal of Comparative Neurology | volume = 168 | issue = 4 | pages = 505–31 | date = August 1976 | pmid = 939820 | doi = 10.1002/cne.901680405 | s2cid = 11826323 }}</ref> Saltatory conduction has also been found in the small- and medium-sized myelinated fibers of ''[[Penaeus]]'' shrimp.<ref>{{cite journal | vauthors = Xu K, Terakawa S | title = Saltatory conduction and a novel type of excitable fenestra in shrimp myelinated nerve fibers | journal = The Japanese Journal of Physiology | volume = 43 Suppl 1 | pages = S285-93 | date = 1993 | pmid = 8271510 }}</ref>

==History of research==
In 1925 Ralph S. Lillie proposed the mechanism of saltatory conduction after experimenting with an iron wire model of the nerve, after covering the wire with isolated sections akin to myelinated internodes he observed a faster and "saltatory" conduction.<ref>{{Cite journal |last=Young |first=Robert G. |last2=Castelfranco |first2=Ann M. |last3=Hartline |first3=Daniel K. |date=June 2013 |title=The “Lillie Transition”: models of the onset of saltatory conduction in myelinating axons |url=http://link.springer.com/10.1007/s10827-012-0435-3 |journal=Journal of Computational Neuroscience |language=en |volume=34 |issue=3 |pages=533–546 |doi=10.1007/s10827-012-0435-3 |issn=0929-5313|hdl=10125/24451 |hdl-access=free }}</ref>

In 1939, [[Ichiji Tasaki]] confirmed saltatory conduction through experiments on isolated [[Nerve|single-nerve fibers]] of the [[Japanese common toad|Japanese Toad]].<ref>{{cite journal |last1=Tasaki |first1=Ichiji |title=Electric Stimulation and the Excitatory Process in the Nerve Fiber |journal=American Journal of Physiology |date=31 Jan 1939 |volume=125 |issue=2|pages=380–395 |doi=10.1152/ajplegacy.1939.125.2.380 }}</ref> Tasaki was experimenting with anaesthetics and noticed a lack of conduction when three or more nodes were anesthetized, leading to his hypothesis.<ref name="auto">{{cite journal |last1=Boullerne |first1=Anne Isabelle |title=The history of myelin |journal=Exp Neurol |date=Sep 2016 |volume=283 |issue=Pt B |pages=431–445 |doi=10.1016/j.expneurol.2016.06.005 |pmid=27288241 |pmc=5010938 }}</ref> During World War II, Tasaki was not able to publish in American journals and had to send manuscripts to Germany via the Siberian railroad. He only heard of their publication after the war ended.<ref name="auto"/>

Lillie's hypothesis was also confirmed by [[Andrew Huxley]] and Robert Stämpfli in peripheral myelinated nerve fibers in 1949 through experiments with isolated frog nerves.<ref>{{cite journal |last1=Huxley AF, Stämpfli R |title=Evidence for saltatory conduction in peripheral myelinated nerve fibres |journal=J Physiol |date=May 15, 1949  |volume=108|issue=3 |pages=315–339 |doi=10.1113/jphysiol.1949.sp004335 }}</ref> Bernhard Frankenhaeuser proved that this was true in undissected frog nerves as well, ending scholarly debate.<ref>{{cite journal |last1=FRANKENHAEUSER |first1=BERNHARD |title=Saltatory conduction in myelinated nerve fibres |journal=J Physiol |date=Sep 1952 |volume=118 |issue=1 |pages=107–112 |doi=10.1113/jphysiol.1952.sp004776 |pmid=13000694 |pmc=1392427 }}</ref>

== See also ==
* [[Bioelectrochemistry]]
* [[Cable theory]]
* [[Electrophysiology]]
* {{annotated link|Ephaptic coupling}}
* {{annotated link|GHK current equation}}
* {{annotated link|Goldman equation}}
* {{annotated link|Hindmarsh–Rose model}}
* {{annotated link|Hodgkin–Huxley model}}
* {{annotated link|Neurotransmission}}
* {{annotated link|Patch clamp}}
* {{annotated link|Quantitative models of the action potential}}
* {{annotated link|Myelination}}

== References ==
{{Reflist|30em}}

== Further reading ==
{{Refbegin}}
* {{cite web | first = Kenneth | last = Saladin | name-list-style = vanc | title = Saltatory conduction | url = https://www.biology-online.org/dictionary/Saltatory_conduction | work = Biology Online }}
* {{cite book |title=Anatomy & physiology : the unity of form and function |isbn=978-0-07-768033-6 |edition=6th | publisher = McGraw-Hill | date = 2011 }}
{{Refend}}

== External links ==
* [http://www.scholarpedia.org/article/Saltatory_conduction Saltatory conduction - Scholarpedia]
* [https://biology.stackexchange.com/questions/8282/why-is-saltatory-conduction-in-myelinated-axons-faster-than-continuous-conductio cell biology - Why is saltatory conduction in myelinated axons faster than continuous conduction in unmyelinated axons?]

{{Authority control}}

{{DEFAULTSORT:Saltatory Conduction}}
[[Category:Neurophysiology]]

[[de:Erregungsleitung#Saltatorische Erregungsleitung]]