Although neurons cannot replicate (mitotically divide), in many cases they may be able to regenerate (repair themselves) after having been traumatized. In the cases of a peripheral nerve, healing and regeneration are likely to occur if the two ends are aligned in case proximity. The distal portion of the axon that was severed from the cell body degenerates and is phagocytosed by Schwann cells and by macrophages that migrate into the trauma zone. Once the debris has been disposed of, the surviving Schwann cells, surrounded by the basement membrane, proliferate to form a regeneration tube as the part of the axon that is connected to the cell body begins to grow and exhibit amoeboid movement. The Schwann cells of the regeneration tube are believed to secrete chemicals that attract the growing axon tip, and the tube itself helps to guide the regenerating axon to its proper destination. Even a major nerve fiber that has been severed can be surgically reconnected and the function of the nerve largely reestablished if the surgery is performed before tissue death has occurred.

Repair of neural damage in the central nervous system is much more problematic. In contrast to peripheral nerve fibers, severed axons of central nerve fibers never regenerate distances of more than 1 mm under normal circumstances. In the CNS, the myelin sheath is formed by oligodendrocytes. Unlike the Schwann cells in the PNS, these supporting cells do not produce growth-promoting chemicals, and they do not proliferate following an injury. Thus, when an axon is damaged in the CNS, no regeneration tube is formed to guide fiber regrowth. Further reducing chances of regeneration is the dense scar tissue that replaces the dead oligodendrocytes. This glial scar, produced by astrocytes to repair structural damage, effective blocks the progress of sprouting axons.

Despite the fact that damage to the brain or spinal cord is generally considered irreversible, experiments in vitro suggest that even axons in the CNS can be stimulated to regenerate to an appreciable extent if an appropriate environment is provided. In a developing fetal brain, chemicals called neurotrophins promote nerve growth. Neurotrophins have also been shown to promote neuron regeneration in adult brains and spinal cords in some experimental animals. Additionally, certain chemicals, including myelin-associated inhibitory proteins, have been shown to inhibit axon regeneration. In a recent experiment, axon regeneration in the spinal cord of a rat was improved by simultaneously providing a neurotrophin and blocking the inhibitory proteins with antibodies.

In other promising research, scientists have found that Schwann cells transplanted to the CNS can promote axonal regeneration. Efforts are also underway to find a means of synthesizing the growth-promoting factor secreted by the Schwann cells. This research holds out hope for scores of accident and stroke victims whose nerve damage is currently irreparable.