Medical Do nerves grow back after injury or not?

[jostpuur]

I've understood that if somebody gets paralyzed as result of injury to the spine, then there is no change of recovery if the injury has been bad enough. (Recovery can occur if the injury is sufficiently mild.) When I've asked about why don't the nerves grow back, I've learned that it simply is the case that they don't grow back.

But then I see stuff like this: http://www.guardian.co.uk/science/2008/oct/08/medicalresearch.germany First double arm transplant patient recovering well

Doctors said there were good indications of nerve growth in the arms but it could take up to two years for Merk to relearn how to use his hands.

If nerves grow back to arms, then why not the the spine too?

 

[Astronuc]

Peripheral nerves do regenerate. I know this from personal experience - after I sliced into my left thumb. Initially there was numbness around the deep cut. After a couple of years or so, the feeling had more or less completely returned.

Then there is this:

Regeneration
Most of the cells in the human body have the ability to repair themselves after an injury. If you cut your finger, often you have a visible laceration for a few days or weeks, followed by the formation of a scar. In time, you may not be able to tell that the cut had occurred. This indicates that skin cells regenerate, just like cells in the blood vessels, organs and many other tissues. Peripheral nerves (nerve fibers outside the brain and spinal cord), such as those located in your fingertips, also regenerate, although this process is different from that in the skin and other organs.

For years, scientists have focused on the big mystery: "Why doesn't the central nervous system regenerate?" This question is even more perplexing because we know that central nerves in lower animal species CAN regenerate. There are no definite answers to this mystery yet, but scientists are exploring the questions in many ways.

http://www.spinalcord.org/news.php?dep=17&page=94&list=1179