The Neuronal cell cycle represents the life cycle of the biological cell, its creation, reproduction and eventual death. The process by which cells divide into two daughter cells is called mitosis. Once these cells are formed they enter G1, the phase in which many of the proteins needed to replicate DNA are made. After G1, the cells enter S phase during which the DNA is replicated. After S, the cell will enter G2 where the proteins required for mitosis to occur are synthesized. Unlike most cell types however, neurons are generally considered incapable of proliferating once they are differentiated, as they are in the adult nervous system. Nevertheless, it remains plausible that neurons may re-enter the cell cycle under certain circumstances. Sympathetic and cortical neurons, for example, try to reactivate the cell cycle when subjected to acute insults such as DNA damage, oxidative stress, and excitotoxicity. This process is referred to as “abortive cell cycle re-entry” because the cells usually die in the G1/S checkpoint before DNA has been replicated.