charles bad, california. >> sanjay gupta is a practicing neurosurgeon. what do you make of this? elena talked about a complete spinal injury. what does that mean? how extensive may they have been? >> it makes a world of difference whether someone has a complete spinal cord injury or incomplete. complete spinal cord injury means the spinal cord had such a significant impact on it, the cells in that area died. incomplete means a lot of different things here. you're looking at a skeleton here, take away any muscle and take away blood vessels over here. this is the spine, designed to protect the spinal cord in yellow. incomplete means there may have been pressure on the back, front, side. the point is this entire spinal cord is not damaged, is there still some possibility of connections getting through. in the world of neurosurgery and rehab, that simple point makes a world of difference. >> this guy is not a doctor, not a physical therapist, basically a trainer.