When a nerve is completely cut, everything it controls goes silent. The area it supplies loses sensation, and if it’s a motor nerve, the muscles it connects to become paralyzed. Within about 36 hours, the portion of the nerve beyond the cut begins to break down in a process called Wallerian degeneration. Whether function returns depends on which nerve was cut, how cleanly it was severed, and how quickly it’s repaired.
What Happens Inside the Nerve Immediately
A nerve isn’t a single wire. It’s a cable made of thousands of individual fibers (axons) bundled together inside protective layers of tissue. When that cable is sliced through, the segment still attached to the brain or spinal cord survives. The segment beyond the cut, now disconnected from its cell body, starts to die.
The breakdown follows a predictable sequence. Within minutes, calcium floods into the severed ends. This calcium surge activates enzymes that begin dismantling the nerve fiber’s internal skeleton. At the same time, the energy molecules that keep the fiber alive hold steady for about two to four hours, then drop sharply. Once energy runs out, the fiber fragments into tiny granules and is cleared away by immune cells over the following days and weeks. This entire cleanup process typically takes one to two weeks, leaving behind hollow tubes of connective tissue where the nerve fibers used to be.
Loss of Sensation and Movement
The effects you feel depend on what type of nerve was cut. Sensory nerves carry information about touch, temperature, and pain. If one is severed, the skin it supplied goes numb. You won’t feel a pinprick, heat, or light touch in that area. Motor nerves control muscles. Cutting one causes immediate paralysis of the muscles it feeds, and you lose the ability to move that part of your body normally. Many nerves carry both sensory and motor fibers, so a single cut can cause numbness and weakness at the same time.
Autonomic nerve fibers, which control things like sweating and blood flow, also run through peripheral nerves. A cut nerve can leave the affected skin dry and pale because sweat glands and blood vessels in the area no longer receive signals.
How Muscles Deteriorate Without a Nerve
Muscles that lose their nerve supply begin to shrink almost immediately. Animal studies show the timeline is aggressive: muscle mass drops by roughly 18% within the first week, nearly 50% by two weeks, and over 60% by five weeks. In humans, the same pattern plays out over weeks to months. The muscle fibers gradually get replaced by fat and scar tissue, and if a nerve signal doesn’t reach them within about 12 to 18 months, the damage becomes largely permanent. This is why the distance between the injury and the muscle matters so much for recovery.
Can a Cut Nerve Regrow?
Peripheral nerves (those outside the brain and spinal cord) can regenerate, but they do so slowly. The regrowth rate is roughly 1 millimeter per day, or about an inch per month. That means a nerve cut in your wrist might take several months to reach the fingertips, while a nerve cut high in the arm or leg could take a year or more to reach the muscles and skin it originally supplied.
The nerve doesn’t regrow on its own after a clean cut. If the two ends are separated, the regenerating fibers have no guide to follow and will grow in disorganized clumps. Surgical repair is almost always needed to reconnect the ends and give the regrowing fibers a path to their targets. Even with surgery, recovery is never instantaneous. You wait weeks to months as the new fibers slowly extend toward their destinations, and function returns gradually, often starting as tingling before progressing to more normal sensation or movement.
How Severity Changes the Outcome
Not all nerve injuries are the same. Doctors classify them on a scale from mildest to most severe:
- Bruised or compressed nerve: The nerve fibers themselves are intact, but the insulating coating is temporarily damaged. Full recovery is expected without surgery.
- Fibers broken, tubes intact: The individual nerve fibers are severed, but the connective tissue tubes surrounding them remain in place. Fibers can regrow along these tubes, and spontaneous recovery is possible.
- Internal scarring: The tubes inside the nerve are damaged and fill with scar tissue. Regrowing fibers may end up in the wrong tubes, leading to incomplete or misdirected recovery. Some fibers meant for one finger might end up supplying another.
- Severe internal damage: Most of the nerve’s internal structure is destroyed, forming a mass of scar tissue called a neuroma-in-continuity. The outer sheath of the nerve is still intact, but signals cannot pass through. Surgery is typically required.
- Complete transection: The nerve is sliced entirely through, with all layers severed. This is the injury most people picture when they think of a “cut nerve.” No recovery is possible without surgical repair.
Surgical Repair and Timing
For a cleanly cut nerve that controls movement, the ideal window for repair is within 24 hours of the injury. When that isn’t possible, repair within 14 days still offers good results, provided the injury happened less than six months ago. For sensory nerves, like the small digital nerves in your fingers, repair within 14 days is also recommended, partly to prevent painful neuroma formation at the cut end.
Injuries from blunt trauma or gunshot wounds are different. The zone of damaged tissue around the injury isn’t always obvious at first, so surgeons often wait two to three weeks for the boundaries of the damage to become clear before operating. Repairing too early in these cases risks connecting healthy nerve to tissue that will later die.
The simplest repair involves stitching the two nerve ends directly together. When a section of nerve is missing and the ends can’t be brought together without tension, surgeons bridge the gap using a nerve graft (a segment of nerve taken from somewhere else in your body, usually a less critical sensory nerve) or a synthetic tube called a conduit that guides the regrowing fibers across short gaps.
What Recovery Feels Like
Recovery after nerve repair is a long process. Because fibers regrow at about an inch per month, a hand injury might take three to six months before you notice returning sensation, while an upper arm injury could take 12 months or longer. The first sign of recovery is often tingling or a “pins and needles” feeling in the affected area. Sensation typically returns before full motor control does.
The quality of recovery depends on several factors: your age (younger people regenerate more effectively), how quickly the nerve was repaired, the type of nerve injured, and the distance the fibers need to travel. Even under ideal conditions, recovery after a complete nerve transection is rarely 100%. Regrowing fibers sometimes enter the wrong tubes and connect to the wrong targets, leading to sensations that feel slightly “off” or muscles that don’t coordinate as smoothly as before.
Neuromas and Chronic Pain
When a cut nerve isn’t repaired, or when repair is incomplete, the regrowing fibers can’t find their way to the other end. Instead, they sprout in all directions at the injury site, tangling with scar tissue and forming a small, firm lump called a traumatic neuroma. These are not tumors. They’re disorganized balls of nerve and connective tissue, typically smaller than 2 centimeters.
Neuromas can be painless, but many are not. The most common symptoms include a tender nodule at the injury site, extreme sensitivity to light touch, and sharp, shooting pain triggered by pressure over the lump. People describe the pain as burning, stabbing, or gnawing. Even clothing brushing against the area can set it off. Neuromas on weight-bearing areas like the foot, or at amputation sites, can be especially disabling. Treatment options range from desensitization therapy and injections to surgical removal or relocation of the nerve ending into a protected area like muscle tissue.
Nerves in the Brain and Spinal Cord
Everything above applies to peripheral nerves, the ones running through your arms, legs, and trunk. Nerves in the brain and spinal cord (the central nervous system) follow different rules. Central nerves produce chemical signals that actively block regrowth, and the scar tissue that forms after injury creates a physical barrier that regenerating fibers cannot cross. This is why spinal cord injuries cause permanent paralysis, while a cut nerve in the hand can potentially recover with surgery. The distinction between peripheral and central nerves is one of the most consequential facts in neuroscience.