Plexus
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204943385
2008-04-11T16:10:21Z
67.151.188.118
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{{unreferenced|date=January 2008}}
{{Wiktionarypar|plexus}}
A '''plexus''' is a network. It has more specific meanings in multiple fields.
==Biology==
In [[biology]] it has multiple meanings.
===Nervous system===
In many animals the processes of [[neuron]]s join together to form a plexus or nerve net.
====In vertebrates====
{{Main|Nerve plexus}}
In vertebrates, a plexus is an area where [[nerve]]s branch and rejoin, for example the [[brachial plexus]] made up of the [[spine (anatomy)|spinal]] nerves which enter the arm and the [[Celiac plexus|solar plexus]] above the [[stomach]].
Almost a hundred such plexuses have been named in the human body, but the four primary [[nerve plexus]]es are the [[cervical plexus]], [[brachial plexus]], [[lumbar plexus]], and the [[sacral plexus]].
====In invertebrates====
Plexuses is the characteristic form of [[nervous system]] in the [[coelenterate]]s and persists with modifications in the [[flatworm]]s. The nerves of the [[symmetry (biology)#Radial symmetry|radially symmetric]] [[echinoderm]]s also take this form, where a plexus underlies the [[germ layer|ectoderm]] of these animals and deeper in the body other [[nerve]] cells form plexuses of limited extent.
===Circulatory system===
A plexus is also a network of [[blood vessel]]s, with the [[choroid plexus]]es of the [[brain]] being the most commonly mentioned example. Choroid plexuses are very thin and vascular roof plates of the most anterior and most posterior cavities of the brain which expand into the interiors of the cavities. Other vascular plexuses are found elsewhere in the body.
[[Category:Nervous system]]
[[Category:Cardiovascular system]]
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