Figure 1. Signal transduction in neuronal cells after nerve injury. The schematic diagram depicts several important signaling pathways activated by axon injury. Cellular injury induces sodium and calcium influx, which lead to depolarization. Among many other processes, the elevated intracellular calcium concentration leads to the activation of protein kinase pathways such as the MAPK Erk1 and Erk2, JNK, and P38 kinase. Downstream events influenced by axotomy-activated kinases include up-regulation or activation of several transcription factors. The modifications in the activity of transcription factors result in characteristic changes of gene expression in the injured and regenerating neurons.