Neurogenesis and Regeneration of Nervous Tissue

Damage to the nervous tissue can be recovered by neurogenesis — the formation of new nerve cells from undifferentiated stem cells, and neuron regeneration — regrowing the damaged nerve cells.

In the CNS, neurogenesis is restricted mainly to the hippocampus of the brain, while neuron regeneration is rare in the entire CNS. Because of this, brain or spinal cord injury is usually permanent.

On the contrary, the neurons of the PNS have a much higher capacity for neuron regeneration. 

Post-injury, the dendrites and myelinated axons of the PNS could regenerate if the cell body is intact, the Schwann cells are functional, and the scar tissue is not immediately formed.

The regeneration process begins with Wallerian degeneration, where the injured axon and myelin sheath are degraded while retaining the neurolemma.

Once macrophages clear the debris by phagocytosis, the Schwann cells on either side of the injury multiply and grow toward each other, forming a regeneration tube. It guides the growth of new axons to complete the regeneration.