The leading candidate myelin-associated molecule that has been shown to stop axonal growth is a protein called Nogo. Oligodendroglial myelin has Nogo on the surface. The antibody called IN-1 blocks Nogo and has been shown to regenerate the spinal cord. Martin Schwab developed this antibody and is likely to go into clinical trial. Other scientists have identified a molecule called myelin-associated glycoprotein or MAG that stops axonal growth.
Axons grow slowly, probably no faster than our hair grows, at about a mm a day at fastest.
Thus, it takes months or years for an axon to grow the entire distance from the injury site back to the neurons that they use to innervate. The axon may simply stop growing after a while. If the axon does not reach a target by a certain time, it stops growing and may die back. Axons that are demyelinated cannot conduct as well. Cells called oligodendroglial cells form myelin around segments of axons.