Neurons have a very limited capacity for regeneration. In general, they neither replicate themselves nor repair themselves. Axons and dendrites in the peripheral nervous system may undergo repair if the cell body is intact and if the Schwann cells are functional. In the central nervous system, however, a damaged or cut axon is usually not repaired even when the cell body is intact and undamaged. Scientists have discovered recently that there are a few small concentrations of neuronal stem cells that remain in adults that can produce a limited number of new neurons.