Each year spinal cord injuries rob some 10,000 Americans of the freedom to move. Now there is a glimmer of hope that victims of severe injuries may some day walk again. Last July, researchers Lars Olson, Henrich Cheng, and Yihao Cao at the Karolinska Institute in Sweden announced that they had succeeded in restoring some muscle function to rats with severed spinal cords.
When we move a muscle voluntarily, a brain neuron sends a signal down its long extension, the axon, to the spinal cord. Brain axons sheathed in myelin, an insulating substance, make up the spinal cord’s white matter, which forms a cylinder around a core of myelin-free motor and sensory neurons--the gray matter. At various points along the spine, axons from the brain leave the white matter and plunge into the gray matter to make contact with motor neurons, which relay signals to the muscles.
The myelin sheath ...
