Apoptosis is programmed cell death, which actively occurs in many physiological processes. It can be triggered in two ways: (i) defects in growth factor, DNA damage, and other many factors that can cause cellular stress, which is an intracellular pathway, and (ii) ligand binding to death receptors and activation of caspases. The apoptotic cell count can be determined by the health of the whole organism. A higher apoptotic ratio can indicate a decrease in the number of cells and tissue damage, while a lower apoptotic ratio can indicate an increase in the number of cells. Irregularity in apoptotic signals can play primary or secondary roles in various diseases/disorders. Research on apoptosis depends on neurodegeneration has been initiated in the past few years. Definition of apoptotic signal pathways and apoptotic regulation and determination of pro- and anti-apoptotic genes are the main topics that have accelerated research on apoptosis. Neurodegenerative disorders such as post-traumatic stress disorder neuronal damage associated with changes in brain structure and function may be related to the mitochondrial stresses. In physiological conditions, apoptosis is crucial for the organism, while in pathological conditions, apoptosis can cause uncontrolled cell division. Development of therapeutic medicine that inhibits the cell death may be the new choice of treatment for neurodegenerative diseases/disorders.