We've had iconic figures like Christopher Reeve, and others, who championed using human embryonic stem cells to treat spinal cord injuries. But the actor died before any clinical trials on humans became a reality.

Now, after years of controversy and hype, treatments have finally begun.

Geron, a biotechnology company, has already enrolled ten patients. Their injury can't be older than two weeks, and must be between the third and tenth thoracic vertebrae.

That's roughly the middle to upper back, with no feeling or movement below the injury.

This phase of the trial is actually not aiming for a cure. The study is evaluating the safety of injecting embryonic stem cells into the spinal cord. Patients are monitored for side effects, like pain and tumor growth.

You may not know that, for most people with spinal cord injuries, the spinal cord is not severed. What's damaged or destroyed is a fatty insulation, called myelin, that coats nerves. Without myelin, nerves cannot send signals down the spinal cord.

The study aims to restore this myelin sheath.

The treatment, called GRNOPC1, takes embryonic stem cells left over from fertility treatments and converts them into cells that produce myelin.

If myelin regrows, the hope is that signals can once again travel along the nerves and restore movement. Researchers hope this phase of the trial will help patients make some basic and significant improvements.

They hope patients will go from wheelchairs to crutches, or have better control over their bowels or bladders.

In animal trials, rats with spinal cord damage could walk and run after treatments with the stem cells. But that's no guarantee the same will happen in humans.

The human clinical trials will take two years, and if they restore even some movement, it will be proof to many that embryonic stem cell treatments hold great promise.