Plexus
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A plexus is a part of nervous system. Plexus has a slightly different definition in vertebrates and in invertebrates.
[edit] In vertebrates
In vertebrates, a plexus is an area where nerves branch and rejoin. The electrical signals do not mix; rather, the fibres travel together with their electrical signals separate. The brachial plexus is an example. It is made up of the spinal nerves which enter the upper limb.
Almost a hundred such plexi have been described in the human body, but the four primary nerve plexi are the cervical plexus, brachial plexus, lumbar plexus, and the sacral plexus.
The choroid plexus is a part of central nervous system in the brain and it consist of capillaries, ventricles and ependymal cells.
[edit] In invertebrates
The plexus is the characteristic form of nervous system in the coelenterates and persists with modifications in the flatworms. The nerves of the radially symmetric echinoderms also take this form, where a plexus underlies the ectoderm of these animals and deeper in the body other nerve cells form plexi of limited extent.
[edit] References
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