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Working Up the Nerve
An outline of the head and back of a human. The brain is highlighted pink, and nerves along the spinal cord and in the back are highlighted yellow.
From paper cuts to broken bones, physical injuries are common occurrences for people of all ages. Generally, these injuries heal because the human body has an amazing capability to generate new cells and tissue to repair itself. But there is one major exception—the nervous system. Unlike other cells in the body, the cells of the central nervous system, those in the brain and spinal cord, do not regenerate after serious injury. Beyond the brain and spinal cord, the remaining portion of the nervous system, the peripheral nervous system, shows some ability to recover; however, the healing there is often slow and incomplete.
The peripheral nervous system includes a network of special cells that send signals throughout the body. These signaling cells, called neurons, are bundled together into nerves of varying lengths. Attached to each neuron is a long fiber called an axon that is responsible for carrying electrical messages to other neurons. Together, neurons and axons connect each body part to the central nervous system, which controls bodily activities. If a person mistakenly touches a hot surface, a chain of axons and neurons delivers that information to the brain. The brain then transmits a message to the muscles, telling them to pull the person's hand away.
When a person's peripheral nervous system is healthy, this entire process can be completed in a fraction of a second. However, sometimes diseases or injuries can damage the fatty outer layer which surrounds and protects the axons, causing them to stop functioning properly. The axon may then send faulty signals or quit working completely. People experiencing this kind of peripheral nerve damage may feel pain, numbness, prickling, burning, or other unpleasant sensations in the part of the body where the axons are injured. They may even lose the ability to control the muscles connected to those nerves.
Recent research has led to a better understanding of how peripheral nerve cells can heal. For example, scientists have discovered that different genes within the neurons must be deactivated, or turned off, to facilitate healing. Turning off these genes prevents the neurons from sending or receiving electrical signals, allowing the cells to better repair themselves. Another area of research has focused on special "helper cells" known as Schwann cells. When the outer layer of an axon is damaged, Schwann cells produce substances that help the axon to regrow. They also assist by breaking down the damaged tissue, cleaning out the area so the axon can recover.
One team of researchers found they could alter the genes of the Schwann cells to trigger them to begin the necessary repairs more quickly. This research may eventually be used to develop treatments for nervous system injuries using cell reprogramming and other genetic techniques, and the discoveries may lead to quicker, more complete healing of peripheral nerve damage. Not only that, but scientists also hope that someday the same principles might be applied to the cells of the central nervous system. Though there is still much work to be done to better understand the mechanisms involved, the research raises the once undreamed-of possibility that even injuries to the brain and spinal cord could someday be healed.
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