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nervous system guide

Spinal Cord Injuries

You've seen the news too often: Someone falls, dives into shallow water, or falls victim to a bullet. The spinal cord is injured, and the medics predict: "This person will never walk again." Over 500,000 young Americans have been paralyzed by spinal cord injuries. Why can't these highly advanced and specialized cells heal?

The spinal cord has two functions in the body: to process simple reflexes and to conduct messages between the brain and peripheral nerves. Like the brain, it has "gray matter" (cells without myelin insulation) and "white matter" (insulated cells.) But in the spine the gray matter is on the inside.

Imagine you touch a hot iron. The message goes from a sensory receptor, through a peripheral nerve, to your spinal cord. In the gray matter, a message is relayed to another nerve - but this one's connected to a muscle, and makes you pull away quickly. That's a simple reflex. The message is also carried by the white matter in the cord up to the brain, and about the time your hand flies away your brain says: "Ouch!"

All those nerves are tightly wrapped within your spinal cord. If they are hit hard and bruised, they want to swell like any other injured cell. But there is no room for swelling. So even if they are not cut or torn, a simple bruise can do permanent damage to the spinal cord's cells, destroying the myelin insulation and forming scar tissue that blocks messages. Because nerve cells are so specialized, they have lost the ability to regrow myelin, break down scar tissue, or heal.

A person who has injured his or her spinal cord might have good reflexes below the injury and be perfectly healthy above. But the sensory feelings from the areas of the body below the injury might not reach the brain, and the commands to move will not reach the muscles.

Not all spinal injuries are hopeless. Sometimes only a fraction of the axons are damaged, and others can be retrained to do their work. Researchers have tried injecting immature cells from bone marrow or the nasal cavity, or even embryo cells, into the injured area to see if they can grow into nerve cells. And research suggests that nerves might be able to heal themselves very, very slowly - over years - if the muscles they control can be kept healthy. But the best cure at present for spinal cord injury is prevention.

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