This chapter describes the reactive changes that central nervous system (CNS) neurons do exhibit following injury, both degenerative responses that occur following denervation and axotomy, and reactive growth that may contribute to recovery of function. Damage to the CNS affects all cell populations in the brain including neurons, glia, ependymal cells, and vascular elements. The chapter explores what happens to neurons and their interconnections. Trauma can cause physical transection of axons (axotomy), causing the portion distal to the injury to degenerate (Wallerian Degeneration). The term "specific regeneration" indicates a specific re-growth of an interrupted axon to its normal target. Developing neurons that have not received their full complement of innervation would be available to the aberrant axons. In mature animals, the prediction is that regenerative sprouting and pruning-related sprouting might not result in the formation of new connections unless sites were made available by denervation.