A plexus is a web-like network where nerves, blood vessels, or other biological structures converge, branch, and reorganize before continuing to their destinations. The term comes from the Latin word for “braid,” and that image fits well: individual strands weave together, exchange fibers, then fan out in new combinations. Most of the time when people encounter the word, it refers to a nerve plexus, but vascular plexuses and other specialized types exist throughout the body.
Why the Body Organizes Nerves Into Plexuses
Spinal nerves exit the spinal cord in neat, segmented pairs, one set per vertebra. But the muscles and skin of your arms, legs, and torso don’t map neatly onto a single spinal segment. Your bicep, for example, needs input from multiple spinal levels to function properly. A plexus solves this problem by mixing fibers from several spinal nerves together, then redistributing them into new bundles that match the body’s actual layout.
This mixing also builds in a degree of redundancy. Because each outgoing nerve carries fibers from multiple spinal roots, damage to a single root doesn’t completely knock out an entire limb. You may lose some strength or sensation, but neighboring roots still contribute through the plexus. It’s an elegant design that balances efficiency with resilience.
The Four Major Nerve Plexuses
Four large somatic nerve plexuses handle sensation and movement for most of your body. Each forms from a specific set of spinal nerves and serves a distinct region.
Cervical Plexus
Located in the neck, this plexus handles the skin of the head, neck, and upper chest through its superficial branches. Its deeper branches control neck muscles and, critically, the diaphragm, the primary muscle you use to breathe. That connection is why a serious neck injury can affect breathing.
Brachial Plexus
The brachial plexus is the complex network responsible for nearly all sensation and movement in the arms. It forms from five spinal nerves in the lower neck and upper back, which reorganize through a specific hierarchy: roots, trunks, divisions, cords, and finally terminal branches that reach the shoulder, arm, forearm, and hand. This is one of the most intricate plexuses in the body and one of the most clinically relevant, since injuries here directly affect arm function.
Lumbar Plexus
Situated in the lower back, the lumbar plexus provides motor and sensory innervation to the lower limbs and pelvic region. Its largest branch, the femoral nerve, powers the muscles at the front of the thigh and provides sensation along the inner leg. Other branches supply the lower abdominal wall, the groin, and the inner thigh. If you’ve ever had numbness or a burning sensation on the outer thigh, that involves the lateral femoral cutaneous nerve, another branch of this plexus.
Sacral Plexus
The sacral plexus sits in the pelvis and gives rise to the sciatic nerve, the thickest nerve in the body. The sciatic nerve controls the back of the thigh and everything below the knee. Other sacral branches supply the gluteal muscles, the skin of the back of the thigh, and the pelvic floor. If you’ve experienced sciatica, the pain radiating down your leg, it traces back to this plexus.
Autonomic Plexuses in the Abdomen
Beyond the four somatic plexuses, a separate set of autonomic plexuses controls organs you don’t consciously move: the stomach, intestines, liver, and pancreas. The most well-known is the celiac plexus, often called the solar plexus. It sits in the upper abdomen near where the main arterial trunk branches off the aorta, roughly behind the stomach. Two clusters of nerve cell bodies form the core of this plexus, and their outgoing fibers wrap around arteries to reach the lower esophagus, stomach, upper small intestine, liver, and pancreas. These nerves regulate digestion, blood flow to the gut, and other functions you never have to think about.
A punch to the “solar plexus” causes that distinctive, breath-stealing pain precisely because this dense nerve network sits just behind the abdominal wall in that area.
Plexuses Inside the Gut Wall
The digestive tract has its own built-in nervous system, sometimes called the “second brain,” and it relies on two plexuses embedded directly in the intestinal wall. The myenteric plexus sits between the two muscle layers of the intestine and is principally responsible for peristalsis, the wave-like contractions that push food through your digestive system. It coordinates specific patterns of contraction and relaxation to keep things moving in the right direction.
A second layer, the submucosal plexus, lies closer to the inner lining and helps regulate fluid secretion and absorption. Together, these two networks allow your gut to manage digestion with remarkable independence from the brain, though the brain can still influence the process through the autonomic plexuses described above.
The Choroid Plexus in the Brain
Not all plexuses involve peripheral nerves. The choroid plexus is a specialized tissue found inside the fluid-filled chambers (ventricles) of the brain, and its primary job is producing cerebrospinal fluid (CSF), the clear liquid that cushions the brain and spinal cord. It consists of tiny, fenestrated blood vessels surrounded by a layer of specialized cells with hair-like projections called cilia, which circulate the CSF, and microvilli, which help absorb it.
The choroid plexus also forms the blood-CSF barrier, a selective checkpoint that prevents harmful substances in the blood from reaching the brain’s fluid environment. Immune cells within the plexus, including macrophages and lymphocytes, add another layer of defense against pathogens. It even secretes growth factors that help maintain the brain’s pool of stem cells.
Venous Plexuses
Plexuses aren’t limited to nerves. Veins can also form plexus-like networks, particularly in areas where blood drainage needs to be flexible or where multiple routes back to the heart provide a safety margin. The pterygoid plexus, for instance, sits deep in the face near the jaw muscles. It collects blood from the nasal cavity, sinuses, and surrounding structures, draining it toward the jugular vein. When the jaw muscles contract during chewing, they create a pumping action that helps push blood through this network.
Other venous plexuses exist around the spine (the vertebral venous plexus) and the reproductive organs. In males, the pampiniform plexus is a network of veins around the testicle that functions as a heat exchanger, cooling arterial blood before it reaches the organ to keep sperm at the right temperature.
What Happens When a Plexus Is Injured
Because plexuses serve as critical relay stations, damage to one can have widespread effects. Brachial plexus injuries are among the most common and illustrate the range of severity well. Minor stretching of the nerves, often called stingers or burners, happens frequently in contact sports like football and wrestling. These typically cause temporary tingling or weakness in the arm and resolve on their own.
More serious injuries occur during car or motorcycle accidents, when the head and shoulder are violently forced in opposite directions. Depending on which part of the plexus is damaged, the result can range from weakness in specific muscles to complete loss of feeling and movement in the arm and hand. The most severe form involves nerve roots being torn from the spinal cord itself, which is far harder to repair than a stretch or rupture further along the nerve.
Newborns can also sustain brachial plexus injuries during difficult deliveries, particularly with high birth weight, prolonged labor, or breech presentation. If the baby’s shoulders become stuck in the birth canal, the upper nerves of the plexus are most vulnerable. This is known as Erb palsy and typically affects the shoulder and upper arm.
Plexus damage isn’t always traumatic. Inflammation, tumors, and autoimmune conditions can also affect these networks, producing gradual weakness, pain, or numbness in the regions they serve.