The survival of cells comprising the nervous system is dependent upon the action of neurotrophic factors that can prevent both intrinsic and extrinsic cues from inducing cellular apoptosis. Apoptosis occurs naturally during homeostasis, in response to injury or viral infection and during neurodegenerative disease.
Apoptosis also plays a crucial role in sculpting the developing nervous system.
Neurons that innervate their targets sooner survive, while neurons that reach the same target later die. While many aspects of neurotrophic factor biology have been accurately predicted by the neurotrophic factor hypothesis, only recently have clues been obtained about the molecular mechanisms of neuronal cell survival and apoptosis.