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
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.