What makes nerves grow

If your nerve is bruised or traumatized but is not cut, it should recover over weeks. Some people notice continued improvement over many months.

Sensory nerves are more resilient than motor nerves and can recover sensation months or years after injury. Motor nerves have a time limit for healing. If the motor endplate receives no nerve impulse for more than months, it dies away and there is no longer any way that the muscle can be activated by the nerve.

The muscle then whithers away. Thus surgical repair of motor nerves needs to happen within months of the injury. Before sensation returns to the injured area, your limb is at risk of damage as it has no protective sensation.

Please be careful of your hands or feet, especially around hot or sharp objects. Similarly, before the motor nerves recover your hand or limb may not be able to move normally or may develop abnormal postures.

Hand therapy or physiotherapy will allow movement to be maintained while the nerve cells regenerate. As your nerve recovers, the area the nerve supplies may feel quite unpleasant and tingly. This may be accompanied by an electric shock sensation at the level of the growing nerve fibres; the location of this sensation should move as the nerve heals and grows.

Over time, these feelings subside and the area should begin to feel more normal. Unfortunately, nerves never recover completely after they have been cut. I use a microscope or magnifying glasses loupes to repair your cut nerve with sutures finer than a human hair.

This type of nerve repair surgery has the best recovery rates. Whether or not I can perform direct nerve repair on your injured limb depends on the injury your nerve has suffered.

Sometimes I cannot directly repair your nerve ends, for example, if there is a piece of nerve missing or a delay in repair. With nerve grafting, I take a length of nerve from somewhere else in your body and place it as a graft. I perform this repair using a microscope, too. The body is capable of regenerating damaged nerves, but this process is slow and incomplete.

Now, researchers at the Eli and Edythe Broad Center of Regenerative Medicine and Stem Cell Research at UCLA have discovered a molecular process that controls the rate at which nerves grow both during embryonic development and recovery from injury throughout life. The study, led by senior author Samantha Butler and published in the Journal of Neuroscience, used experiments with mice to show that it is possible to accelerate peripheral nerve growth by manipulating this molecular process.

The finding could inform the development of therapies that reduce the time it takes for people to recover from nerve injuries. Peripheral nerves extend over long distances to connect limbs, glands and organs to the brain and spinal cord, sending signals that control movement via motor neurons, and relaying information such as pain, touch and temperature via sensory neurons.

Unlike the nerves in the brain and spinal cord, which are protected by the skull and vertebrae, the nerves of the peripheral nervous system have no such protection, leaving them vulnerable to injury. While the body has a mechanism to help peripheral nerves reestablish connections after injury, this process is slow; damaged nerves regrow at an average rate of just one millimeter per day.

For instance, cells in the liver and the endothelial cells that line blood vessels. But, the new study shows, the Schwann cells need help to repair the nerves properly. That help comes from a well-studied cell type known to play a role in wound healing: fibroblasts.

This shows that they act in a completely new way. The fibroblasts send a signal to the Schwann cells, causing them to sort themselves into clumps, or cords, that make their way out of the nerve stump as a group. Those cords guide the regrowth of axons across the wound.

Lloyd's team found that the response to the so-called ephrin-B signal issued by the fibroblasts depends on a factor called Sox2, best known for its central role in embryonic stem cells. Sox2 is also one of a handful of ingredients that can help reprogram adult cells to behave like embryonic stem cells. Without the ephrin-B signal, Schwann cells fail to migrate in an organized fashion and the axons don't grow back properly.

Lloyd said the new findings might lead to ways to improve the repair of peripheral nerves, noting that the natural process isn't all that efficient. Her team is actively exploring ways to improve upon the natural nerve-healing mechanism now. The researchers also have plans to investigate whether similar mechanisms might be involved in the movement and spread of cancers of the peripheral nervous system.