Why neurons die: cell death in the nervous system.

It is likely that humans are born with all of the nerve cells (neurons) that will serve them throughout life. For all practical purposes, when our neurons die, they are lost forever. During nervous system development, about one-and-a-half times the adult number of neurons are created. These "extra" neurons are then destroyed or commit suicide. This process of programmed cell death occurs through a series of events termed apoptosis and is an appropriate and essential event during brain development. Later in life, inappropriate neuronal cell death may result from pathological causes such as traumatic injury, environmental toxins, cardiovascular disorders, infectious agents, or genetic diseases. In some cases, the death occurs through apoptosis. In other cases, cell death is random, irreversible, and uncontrollable; to distinguish it from the controlled, planned cell death of apoptosis, we call this necrotic cell death. Understanding the difference between apoptotic and necrotic cell death is essential for designing therapies which will prevent or limit inappropriate cell death in the nervous system.