Today at dinner, we were discussing the phenomena of the wheelchair bound in society and we realized they come in two basic ‘flavors’. That is, those who have some or all control of their upper body, and those that are almost entire immobilized. Now, I know that the spinal cord is fairly ‘simple’ and presumably the higher up the cord the injury is, the more of the cord below that point essentially doesn’t work.
The question no one could answe,r though, is whether it is possible (either through disease or injury) to have the middle section of the cord not work, but have the top and bottom function. In other words, is there such a thing as a paraplegic who can walk and is otherwise mentally o.k. but has no use of their arms?
I think for that to happen, you’d have to have a functioning brain in your butt as well as in your noggin. 
Your brain sends out signals to your body via the central nervous system. Your brain also receives signals from your body via the central nervous system. Serious damage to the spinal cord will simply cut off the signals. I don’t think there’s any way that the area below the damaged cord could bypass the damage section.
No, it’s not possible. There’s not really a bypass function in quad/paraplegics. However, there are different kinds of damage… for example, some people in wheelchairs still retain control over their bowels, urination, and sexual functions, while others don’t. It depends on what was hit.
http://www.spinalcord.uab.edu/ is quite a good resource for more information.