The peripheral nervous system (PNS) is your body’s communication network between the brain and spinal cord and everything else: your skin, muscles, organs, and glands. Its job is to carry sensory information inward and motor commands outward, connecting your central nervous system to the rest of your body through 43 pairs of nerves. Without it, your brain would have no way to feel the world or act on it.
How the PNS Is Organized
The peripheral nervous system has two major divisions, each handling a different category of work. The somatic nervous system connects to your skin and muscles and handles conscious activities, things you decide to do like picking up a cup or walking across a room. The autonomic nervous system connects to your internal organs (heart, stomach, intestines, lungs) and manages unconscious activities, processes that happen without you thinking about them.
These two divisions use the same basic hardware. You have 12 pairs of cranial nerves that originate in your brain and extend through your face, head, and neck. Below that, 31 pairs of spinal nerves branch out from your spinal cord and reach into your trunk, arms, and legs. Together, these nerve pairs form the physical wiring of the PNS.
Gathering Sensory Information
One of the PNS’s primary jobs is collecting data about your environment and your own body, then relaying it to the brain for processing. It does this through specialized sensory receptors, each tuned to a different type of stimulus.
Mechanoreceptors respond to physical stimuli like pressure, vibration, and stretch. They’re the basis for your sense of touch, hearing, and balance. When you feel the texture of fabric between your fingers or sense that you’re tilting sideways, mechanoreceptors are generating those signals. Thermoreceptors detect temperature changes, with separate receptors for heat and cold relative to normal body temperature. Nociceptors handle pain. They activate when mechanical, chemical, or thermal stimuli cross a certain intensity threshold. Damaged tissues release chemicals that trigger these receptors, which is why an injury keeps hurting even after the initial impact. Chemoreceptors detect chemical stimuli and underlie your senses of smell and taste.
All of these receptors convert their respective stimuli into electrical signals that travel along sensory nerves toward the brain and spinal cord. The speed of transmission varies depending on the nerve fiber type. Large, insulated fibers carrying touch and muscle-position signals can conduct impulses at 40 to 65 meters per second. Smaller pain fibers transmit more slowly, which is why you often feel a sharp touch before the ache that follows it.
Controlling Voluntary Movement
The somatic nervous system carries motor commands from your brain to your skeletal muscles. Every deliberate movement you make, from typing to running, requires signals that originate in the brain, travel down the spinal cord, and then pass through peripheral motor nerves to reach the appropriate muscles.
At the endpoint of each motor nerve, the electrical signal converts to a chemical signal at a junction called a synapse. That chemical message triggers the muscle fiber to contract. This happens fast enough to feel instantaneous, but it’s a precise chain of events: brain generates command, peripheral nerve carries it, muscle responds. If the peripheral nerve is damaged along the way, the muscle it serves weakens or stops working entirely.
The Sympathetic System: Reacting to Stress
The autonomic nervous system splits into two branches that often work in opposition. The sympathetic branch activates during stress or danger, producing what’s commonly called the fight-or-flight response. When it kicks in, several things happen at once: your heart rate increases, your breathing capacity improves, your pupils dilate to let in more light, and your liver releases stored energy in a form your body can use quickly. At the same time, digestion slows down so that energy can be diverted to muscles and the brain.
These changes aren’t just for life-threatening situations. Your sympathetic system ramps up during exercise, job interviews, or any moment that demands alertness. The combined effect is improved eyesight, faster reflexes, and greater endurance and strength, all managed automatically by your peripheral nerves without any conscious decision on your part.
The Parasympathetic System: Rest and Recovery
The parasympathetic branch does the opposite. It dominates when you’re safe, relaxed, and recovering. It lowers your heart rate and reduces the pumping force of your heart. It speeds up digestion and signals your pancreas to release insulin, helping your cells convert sugars into usable energy. It triggers saliva production in your mouth, which aids both digestion and breathing during rest. It also relaxes the muscles that control urination and bowel movements.
Think of the two branches as a gas pedal and a brake. The sympathetic system accelerates your body’s readiness, while the parasympathetic system slows things down and redirects resources toward maintenance and repair. Your body constantly adjusts the balance between them based on what you’re doing and what’s happening around you.
The Gut’s Own Nervous System
There’s a third, often overlooked part of the PNS: the enteric nervous system, sometimes called “the second brain.” This is a dense network of neurons embedded in the walls of your gastrointestinal tract. It contains sensory neurons, motor neurons, and interneurons that form complete reflex circuits capable of controlling gut motility, secretion, and blood flow independently of the brain.
Profiling studies have identified thousands of individual neurons in the enteric system organized into at least five broad types: sensory neurons that detect conditions inside the gut, excitatory and inhibitory motor neurons that speed up or slow down intestinal contractions, secretomotor neurons that regulate fluid release, and interneurons that connect the others into functional circuits. This is why your digestive system can keep working even when communication with the brain is limited.
What Happens When Peripheral Nerves Are Damaged
Because the PNS touches nearly every part of your body, damage to it can produce a wide range of symptoms. The most common form of PNS dysfunction is peripheral neuropathy, and its leading cause is diabetes. Over time, high blood sugar and elevated triglycerides damage both the nerves themselves and the tiny blood vessels that supply them with nutrients.
Symptoms of peripheral neuropathy typically start in the feet and hands and can include burning, tingling (“pins and needles”), numbness, pain, and weakness. You might feel extreme pain from a light touch, or lose the ability to sense temperature changes. As it progresses, peripheral neuropathy can cause loss of balance, changes in the way you walk, loss of muscle tone in the hands and feet, and swollen feet. Symptoms are often worse at night and usually affect both sides of the body, though one-sided symptoms are possible.
One important difference between the PNS and the central nervous system is that peripheral nerves have some capacity to regrow after injury. Recovery is slow and not always complete, but the potential for regeneration is there, which is why some people with nerve damage gradually regain sensation or strength over months.