Editing Action potential (section)

==Taxonomic distribution and evolutionary advantages==
Action potentials are found throughout [[multicellular organism]]s, including [[plant]]s, [[invertebrate]]s such as [[insect]]s, and [[vertebrate]]s such as [[reptile]]s and [[mammal]]s.<ref name=Fromm group=lower-alpha>{{cite journal | vauthors = Fromm J, Lautner S | title = Electrical signals and their physiological significance in plants | journal = Plant, Cell & Environment | volume = 30 | issue = 3 | pages = 249–257 | date = March 2007 | pmid = 17263772 | doi = 10.1111/j.1365-3040.2006.01614.x | doi-access = free | bibcode = 2007PCEnv..30..249F }}</ref> [[Sponge]]s seem to be the main [[phylum]] of multicellular [[eukaryote]]s that does not transmit action potentials, although some studies have suggested that these organisms have a form of electrical signaling, too.<ref group=lower-alpha>{{cite journal | vauthors = Leys SP, Mackie GO, Meech RW | title = Impulse conduction in a sponge | journal = The Journal of Experimental Biology | volume = 202 (Pt 9) | issue = 9 | pages = 1139–50 | date = May 1999 | doi = 10.1242/jeb.202.9.1139 | pmid = 10101111 | bibcode = 1999JExpB.202.1139L | url = http://jeb.biologists.org/cgi/pmidlookup?view=long&pmid=10101111 }}</ref> The resting potential, as well as the size and duration of the action potential, have not varied much with evolution, although the [[conduction velocity]] does vary dramatically with axonal diameter and myelination.

{| class="wikitable" id="action_potential_texonomic_comparison" align="center"
|+ Comparison of action potentials (APs) from a representative cross-section of animals{{sfn|Bullock|Horridge|1965}}
! Animal !! Cell type !! Resting potential (mV) !! AP increase (mV) !! AP duration (ms) !! Conduction speed (m/s)
|-
| Squid (''Loligo'') || Giant axon || −60 || 120 || 0.75 || 35
|-
| Earthworm (''Lumbricus'') || Median giant fiber || −70 || 100 || 1.0 || 30
|-
| Cockroach (''Periplaneta'') || Giant fiber || −70 || 80–104 || 0.4 || 10
|-
| Frog (''Rana'') || Sciatic nerve axon || −60 to −80 || 110–130 || 1.0 || 7–30
|-
| Cat (''Felis'') || Spinal motor neuron || −55 to −80 || 80–110 || 1–1.5 || 30–120
|}

Given its conservation throughout evolution, the action potential seems to confer evolutionary advantages. One function of action potentials is rapid, long-range signaling within the organism; the conduction velocity can exceed 110&nbsp;m/s, which is one-third the [[speed of sound]]. For comparison, a hormone molecule carried in the bloodstream moves at roughly 8&nbsp;m/s in large arteries. Part of this function is the tight coordination of mechanical events, such as the contraction of the heart. A second function is the computation associated with its generation. Being an all-or-none signal that does not decay with transmission distance, the action potential has similar advantages to [[digital electronics]]. The integration of various dendritic signals at the axon hillock and its thresholding to form a complex train of action potentials is another form of computation, one that has been exploited biologically to form [[central pattern generator]]s and mimicked in [[artificial neural network]]s.

The common prokaryotic/eukaryotic ancestor, which lived perhaps four billion years ago, is believed to have had voltage-gated channels. This functionality was likely, at some later point, cross-purposed to provide a communication mechanism. Even modern single-celled bacteria can utilize action potentials to communicate with other bacteria in the same [[biofilm]].<ref>{{cite journal | vauthors = Kristan WB | title = Early evolution of neurons | journal = Current Biology | volume = 26 | issue = 20 | pages = R949–R954 | date = October 2016 | pmid = 27780067 | doi = 10.1016/j.cub.2016.05.030 | doi-access = free | bibcode = 2016CBio...26.R949K }}</ref>