Nerves are the body’s internal wiring system, carrying electrical and chemical signals between your brain, spinal cord, and every other part of your body. You have billions of individual nerve cells, but they’re bundled together into cable-like structures called nerves that branch out to reach your skin, muscles, organs, and glands. These signals travel at speeds ranging from less than 1 meter per second up to 120 meters per second, depending on the type of nerve fiber involved.
How a Nerve Is Built
A single nerve isn’t just one fiber. It’s a layered bundle, structured a bit like a telephone cable. At the center are axons, long cord-like fibers that carry electrical signals. Branching off from nerve cells are dendrites, which receive incoming signals from other cells. These fibers are organized into groups called fascicles, and each layer has its own protective wrapping.
The innermost layer, called the endoneurium, wraps around individual axons. The perineurium surrounds each fascicle (a bundle of axons). And the outermost layer, the epineurium, covers the entire nerve like a sheath. This layered design protects the delicate fibers inside from compression and stretching as you move throughout the day.
The Three Functional Types of Nerves
Not all nerves do the same job. They fall into three broad categories based on what kind of information they carry.
- Sensory nerves carry information from your body to your brain. These handle everything you feel and perceive: touch, temperature, pain, sound, smell, and taste.
- Motor nerves carry commands from your brain to your muscles. Every time you walk, pick up a cup, or turn your head, motor nerves are delivering the signal that makes it happen.
- Autonomic nerves manage the processes you never have to think about: heart rate, digestion, blood pressure, breathing, and sweating. These work whether you’re awake or asleep.
The autonomic nerves break down further into two opposing systems. The sympathetic system ramps your body up during stress or danger, triggering the “fight or flight” response. The parasympathetic system does the opposite, slowing things down for rest and digestion. A third branch, the enteric nervous system, specifically manages digestion and operates with a surprising degree of independence from the brain.
How Nerves Are Organized in the Body
Your nervous system has two main divisions. The central nervous system consists of the brain and spinal cord. The peripheral nervous system includes every nerve that branches out from there into the rest of your body.
From the brain itself, 12 pairs of cranial nerves emerge. These handle specialized tasks in the head and neck, including vision, hearing, facial movement, and the sense of smell. From the spinal cord, 31 pairs of spinal nerves branch out: 8 cervical (neck), 12 thoracic (mid-back), 5 lumbar (lower back), 5 sacral (pelvis), and 1 coccygeal (tailbone).
These spinal nerves don’t simply run in straight lines to their destinations. In several regions, they merge and rebranch into networks called plexuses. The brachial plexus, for instance, is a web of nerves in the shoulder area that sorts signals headed to your arms and hands. The lumbar and sacral plexuses do the same for your legs and pelvis. This design allows fibers from multiple spinal levels to combine into the specific nerves your limbs need.
The sciatic nerve, which runs from the lower back down through each leg, is the largest and longest nerve in the body. It sits deep within the thigh, roughly 6.5 to 7 centimeters below the skin surface in most people.
How Nerve Signals Travel
Nerve signaling is a two-part process: part electrical, part chemical. The electrical phase happens along the length of a nerve fiber. When a nerve cell is stimulated enough to cross a certain voltage threshold, it fires an electrical impulse called an action potential. This impulse races down the axon toward its destination.
When the signal reaches the end of one nerve cell, it has to jump across a tiny gap (about 20 to 40 nanometers wide) to reach the next cell. Here, the process switches from electrical to chemical. The arriving signal triggers the release of chemical messengers, which float across the gap and bind to receptors on the receiving cell. That binding converts the chemical signal back into an electrical one, and the cycle repeats along the next nerve fiber.
Why Some Signals Travel Faster Than Others
Many nerve fibers are wrapped in a fatty insulating layer called myelin. This coating doesn’t cover the entire fiber continuously. Instead, it leaves small exposed gaps at regular intervals. Electrical signals essentially leap from one gap to the next rather than crawling along the full length of the fiber. This jumping pattern dramatically increases speed while using less energy.
The thickest, most heavily insulated motor fibers can conduct signals at 80 to 120 meters per second, fast enough to send a command from your brain to your foot in a fraction of a second. Thinner fibers with less insulation are slower, conducting at 4 to 24 meters per second. The smallest unmyelinated fibers, like those carrying dull, aching pain, move signals at less than 1 meter per second. Speed is directly proportional to the diameter of the fiber: fatter nerves conduct faster.
How Damaged Nerves Heal
One important difference between the central and peripheral nervous systems is repair capacity. Nerves in the brain and spinal cord have very limited ability to regrow after injury. Peripheral nerves, the ones running through your arms, legs, and torso, can regenerate, but slowly.
The baseline regrowth rate for peripheral nerves is about 1 millimeter per day, or roughly one inch per month. Some nerves recover faster than others. The radial nerve in the arm, for example, can regenerate at 4 to 5 millimeters per day, while the ulnar nerve (the one responsible for “funny bone” sensations) regrows at about 1.5 millimeters per day. This means recovery from a significant nerve injury can take months or even years depending on how far the nerve needs to regrow to reach its target muscle or skin area.
Nutrients That Keep Nerves Healthy
The myelin coating that insulates nerve fibers requires specific nutrients to stay intact. Vitamin B12 is the most well-known: a deficiency directly damages the myelin sheath, which can lead to numbness, tingling, and weakness. This is one reason B12 deficiency is taken seriously even when other blood markers look normal.
B12 isn’t the only nutrient involved. Deficiencies in vitamins B1, B6, B9 (folic acid), and E, as well as the mineral copper, can all cause nerve damage. People at higher risk for these deficiencies include those with digestive conditions that impair nutrient absorption, those who follow highly restrictive diets, and heavy alcohol users. The damage from nutritional deficiencies is often reversible if caught early, but prolonged deficiency can cause lasting nerve injury.