G0 phase

Many mammal cells, such as this 9x Hneuron, remain permanently or semipermanently in G₀.

The G₀ phase, G zero alpha phase, or 'resting phase' is a period in the cell cycle in which cells exist in a quiescent state. Mammalian cell devision cycle is controlled with extreme precision in order to complete the duplication of the genome and the segregation of replicated chromosome to daughter cells.^[1] G₀ phase is viewed as either an extended G₁ phase, where the cell is neither dividing nor preparing to divide, or a distinct quiescent stage that occurs inside of the cell cycle.^[2] Some types of cells, such as nerve and heart muscle cells, become quiescent when they reach maturity (i.e., when they are terminally differentiated) but continue to perform their main functions for the rest of the organism's life. Multinucleated muscle cells that do not undergo cytokinesis are also often considered to be in the G₀ stage.^[2] On occasion, a distinction in terms is made between a G₀ cell and a 'quiescent' cell (e.g., heart muscle cells and neurons), which will never enter the G₁ phase, whereas other G₀ cells may.

Distinction from senescent cells

Cellular senescence is distinct from quiescence because it is a state that occurs in response to DNA damage or degradation that would make a cell's progeny nonviable. Senescence then, unlike quiescence, is often a biochemical alternative to the self-destruction of such a damaged cell by apoptosis. Furthermore, quiescence is reversible whereas senescence is not.^[3][4]

References

See also