Editing Nerve (section)

==Other animals==
{{Cleanup rewrite|"neuron" does not coincide with "nerve"|section|date=April 2025}}
A neuron is called ''identified'' if it has properties that distinguish it from every other neuron in the same animal—properties such as location, neurotransmitter, gene expression pattern, and connectivity—and if every individual organism belonging to the same species has exactly one neuron with the same set of properties.<ref name=Hoyle>{{Cite book|title=Identified neurons and behavior of arthropods |publisher=Plenum Press |year=1977 |isbn=978-0-306-31001-0 |vauthors=Hoyle G, Wiersma CA }}</ref>  In vertebrate nervous systems, very few neurons are "identified" in this sense. Researchers believe humans have none—but in simpler nervous systems, some or all neurons may be thus unique.<ref name=Wormbook>{{Cite web |title=Wormbook: Specification of the nervous system |url=http://www.wormbook.org/chapters/www_specnervsys/specnervsys.html |url-status=live |archive-url=https://web.archive.org/web/20110717081646/http://www.wormbook.org/chapters/www_specnervsys/specnervsys.html |archive-date=2011-07-17 }}</ref>

In vertebrates, the best known identified neurons are the gigantic [[Mauthner cell]]s of fish.<ref name=Stein>{{Cite book|title=Neurons, Networks, and Motor Behavior |last=Stein |first=PSG |publisher=MIT Press |date=1999 |isbn=978-0-262-69227-4}}</ref>{{rp|38–44}} Every fish has two Mauthner cells, located in the bottom part of the brainstem, one on the left side and one on the right. Each Mauthner cell has an axon that crosses over, innervating (stimulating) neurons at the same brain level and then travelling down through the spinal cord, making numerous connections as it goes. The synapses generated by a Mauthner cell are so powerful that a single action potential gives rise to a major behavioral response: within milliseconds the fish curves its body into a [[Mauthner cell#The C-start behavior|C-shape]], then straightens, thereby propelling itself rapidly forward. Functionally of this is a fast escape response, triggered most easily by a strong sound wave or pressure wave impinging on the lateral line organ of the fish. Mauthner cells are not the only identified neurons in fish—there are about 20 more types, including pairs of "Mauthner cell analogs" in each spinal segmental nucleus. Although a Mauthner cell is capable of bringing about an escape response all by itself, in the context of ordinary behavior other types of cells usually contribute to shaping the amplitude and direction of the response.

Mauthner cells have been described as [[command neuron]]s. A command neuron is a special type of identified neuron, defined as a neuron that is capable of driving a specific behavior all by itself.<ref name=Stein/>{{rp|112}} Such neurons appear most commonly in the fast escape systems of various species—the [[squid giant axon]] and [[squid giant synapse]], used for pioneering experiments in neurophysiology because of their enormous size, both participate in the fast escape circuit of the squid. The concept of a command neuron has, however, become controversial, because of studies showing that some neurons that initially appeared to fit the description were really only capable of evoking a response in a limited set of circumstances.<ref name=Simmons43>{{Cite book|title=Nerve Cells and Animal Behaviour |url=https://archive.org/details/nervecellsanimal00simm_659 |url-access=limited |publisher=Cambridge University Press |year=1999 |isbn=978-0-521-62726-9 |page=[https://archive.org/details/nervecellsanimal00simm_659/page/n53 43] |vauthors=Simmons PJ, Young D }}</ref>

In organisms of [[radial symmetry]], [[nerve net]]s serve for the nervous system. There is no brain or centralised head region, and instead there are interconnected neurons spread out in nerve nets. These are found in [[Cnidaria]], [[Ctenophora]] and [[Echinodermata]].