is a network. It has more specific meanings in multiple fields.
it has multiple meanings.
In many animals the processes of neurons
join together to form a plexus or nerve net.
In vertebrates, a plexus is an area where nerves
branch and rejoin, for example the brachial plexus
made up of the spinal
nerves which enter the arm and the solar plexus
above the stomach
Almost a hundred such plexuses have been named in the human body, but the four primary nerve plexuses are the cervical plexus, brachial plexus, lumbar plexus, and the sacral plexus.
Plexuses 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 plexuses of limited extent.
A plexus is also a network of blood vessels
, with the choroid plexuses
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.