Figure 1. Wound healing, secondary damage, and abortive regeneration in the central nervous system.

The lesion cavity of a central nervous system injury expands as inflammatory cells interact with the surrounding reactive astrocytes and other reactive glial cells. This region of glial scarring is associated with upregulation of inhibitory extracellular matrix molecules, such as proteoglycans, that are distributed in an increasing concentration gradient from the lesion penumbra to the lesion center. This intense inflammatory response leads to a cascade of secondary damage to axons initially spared from direct trauma, and demyelination of adjacent axons that are not readily re-myelinated by adult oligodendrocytes and precursor cells. The gradient of inhibitory molecules upregulated in the areas of intense inflammation provides an environment that is nonpermissive for regeneration, and dystrophic neurons develop the classically-described sterile end-balls with clubbed endings that are characteristic of abortive attempts at regeneration.