A
plexus is a
networkNetwork may refer to:* Network science** Network , a type of digraph in graph theory** Network theory, an area of applied mathematics and part of graph theory* Network analysis * Network diagram, a diagram of a network...
. In
biologyBiology is the natural science concerned with the study of life and living organisms, including their structure, function, growth, origin, evolution, distribution, and taxonomy...
the term
plexus has multiple meanings:
In many animals the processes of
neuronA neuron is an excitable cell in the nervous system that processes and transmits information by electrochemical signaling. Neurons are the core components of the brain, the vertebrate spinal cord, the invertebrate ventral nerve cord, and the peripheral nerves...
s join together to form a plexus or nerve net.
In vertebrates, a plexus is an area where
nerveA nerve is an enclosed, cable-like bundle of peripheral axons . A nerve provides a common pathway for the electrochemical nerve impulses that are transmitted along each of the axons. Nerves are found only in the peripheral nervous system...
s branch and rejoin. The electrical signals do not mix - rather, the fibres travel together with their electrical signals separate. The
brachial plexusThe brachial plexus is an arrangement of nerve fibers, running from the spine, formed by the ventral rami of the lower cervical and upper thoracic nerve root, specifically from below the fifth cervical vertebra to above the first thoracic vertebra...
is an example. It is made up of the spinal nerves which enter the upper limb.
Almost a hundred such plexuses have been described in the human body, but the four primary
nerve plexusA nerve plexus is a network of intersecting nerves. They combine sets of spinal nerves that serve the same area of the body into one large grouped nerve...
es are the
cervical plexusThe cervical plexus is a plexus of the ventral rami of the first four cervical spinal nerves which are located from C1 to C4 cervical segment in the neck. They are located laterally to the transverse processes between prevertebral muscles from the medial side and vertebral from lateral side...
,
brachial plexusThe brachial plexus is an arrangement of nerve fibers, running from the spine, formed by the ventral rami of the lower cervical and upper thoracic nerve root, specifically from below the fifth cervical vertebra to above the first thoracic vertebra...
,
lumbar plexusThe lumbar plexus is a nervous plexus in the lumbar region of the body which forms part of the lumbosacral plexus. It is formed by the ventral divisions of the first four lumbar nerves and from contributions of the subcostal nerve , which is the the last thoracic nerve...
, and the
sacral plexusIn human anatomy, the sacral plexus is a nerve plexus which, as part of the lumbosacral plexus, emerges from the sacral vertebrae , and which provides motor and sensory nerves for the posterior thigh, most of the lower leg, the entire foot, and part of the pelvis.-Composition:The sacral plexus is...
.
Plexuses is the characteristic form of
nervous systemThe nervous system is a network of specialized cells that communicate information about an organism's surroundings and itself. It processes this information and causes reactions in other parts of the body. It is composed of neurons and other specialized cells called glial cells that aid in the...
in the coelenterates and persists with modifications in the
flatwormThe flatworms, known in scientific literature as Platyhelminthes are a phylum of relatively simple bilaterian, unsegmented, soft-bodied invertebrate animals...
s.
A
plexus is a
networkNetwork may refer to:* Network science** Network , a type of digraph in graph theory** Network theory, an area of applied mathematics and part of graph theory* Network analysis * Network diagram, a diagram of a network...
. In
biologyBiology is the natural science concerned with the study of life and living organisms, including their structure, function, growth, origin, evolution, distribution, and taxonomy...
the term
plexus has multiple meanings:
Nervous system
In many animals the processes of
neuronA neuron is an excitable cell in the nervous system that processes and transmits information by electrochemical signaling. Neurons are the core components of the brain, the vertebrate spinal cord, the invertebrate ventral nerve cord, and the peripheral nerves...
s join together to form a plexus or nerve net.
In vertebrates
In vertebrates, a plexus is an area where
nerveA nerve is an enclosed, cable-like bundle of peripheral axons . A nerve provides a common pathway for the electrochemical nerve impulses that are transmitted along each of the axons. Nerves are found only in the peripheral nervous system...
s branch and rejoin. The electrical signals do not mix - rather, the fibres travel together with their electrical signals separate. The
brachial plexusThe brachial plexus is an arrangement of nerve fibers, running from the spine, formed by the ventral rami of the lower cervical and upper thoracic nerve root, specifically from below the fifth cervical vertebra to above the first thoracic vertebra...
is an example. It is made up of the spinal nerves which enter the upper limb.
Almost a hundred such plexuses have been described in the human body, but the four primary
nerve plexusA nerve plexus is a network of intersecting nerves. They combine sets of spinal nerves that serve the same area of the body into one large grouped nerve...
es are the
cervical plexusThe cervical plexus is a plexus of the ventral rami of the first four cervical spinal nerves which are located from C1 to C4 cervical segment in the neck. They are located laterally to the transverse processes between prevertebral muscles from the medial side and vertebral from lateral side...
,
brachial plexusThe brachial plexus is an arrangement of nerve fibers, running from the spine, formed by the ventral rami of the lower cervical and upper thoracic nerve root, specifically from below the fifth cervical vertebra to above the first thoracic vertebra...
,
lumbar plexusThe lumbar plexus is a nervous plexus in the lumbar region of the body which forms part of the lumbosacral plexus. It is formed by the ventral divisions of the first four lumbar nerves and from contributions of the subcostal nerve , which is the the last thoracic nerve...
, and the
sacral plexusIn human anatomy, the sacral plexus is a nerve plexus which, as part of the lumbosacral plexus, emerges from the sacral vertebrae , and which provides motor and sensory nerves for the posterior thigh, most of the lower leg, the entire foot, and part of the pelvis.-Composition:The sacral plexus is...
.
In invertebrates
Plexuses is the characteristic form of
nervous systemThe nervous system is a network of specialized cells that communicate information about an organism's surroundings and itself. It processes this information and causes reactions in other parts of the body. It is composed of neurons and other specialized cells called glial cells that aid in the...
in the coelenterates and persists with modifications in the
flatwormThe flatworms, known in scientific literature as Platyhelminthes are a phylum of relatively simple bilaterian, unsegmented, soft-bodied invertebrate animals...
s. The nerves of the radially symmetric
echinodermEchinoderm, there are seven main classes of Echinoderms which are brittle stars, basket stars, sea urchins, sand dollars, sea lilies, feather stars, and sea cucumbers...
s also take this form, where a plexus underlies the
ectodermA germ layer is a group of cells, formed during animal embryogenesis. Germ layers are particularly pronounced in the vertebrates; however, all animals more complex than sponges produce two or three primary tissue layers...
of these animals and deeper in the body other
nerveA nerve is an enclosed, cable-like bundle of peripheral axons . A nerve provides a common pathway for the electrochemical nerve impulses that are transmitted along each of the axons. Nerves are found only in the peripheral nervous system...
cells form plexuses of limited extent.
Circulatory system
A plexus is also a network of
blood vesselThe blood vessels are the part of the circulatory system that transport blood throughout the body. There are three major types of blood vessels: the arteries, which carry the blood away from the heart, the capillaries, which enable the actual exchange of water and chemicals between the blood and...
s. The
choroid plexusThe choroid plexus is the area on the ventricles of the brain where cerebrospinal fluid is produced by modified ependymal cells.-Locations:...
of the
brainThe brain is the center of the nervous system in all vertebrate, and most invertebrate, animals. Some primitive animals such as jellyfish and starfish have a decentralized nervous system without a brain, while sponges lack any nervous system at all...
is an example.
In a vascular plexus, the contents of the vessels mix. A plexus allows blood to flow via multiple routes. If one branch of the plexus is obstructed, the blood may flow via the open branches.