A quiescent cell that does not go into mitosis, or a cell destined to die, enters the G0 phase of the cell cycle. The G0 phase of the cell cycle actively represses mitosis, or cell division.
A cell enters the G0 phase by coming out of the cell cycle at the G1 checkpoint. Sometimes, a cell remains in G0 for its entire lifetime. Human nerve cells and skeletal muscle cells usually reside in the G0 phase, as do most other cells in human beings. At the G1 phase, if the cell receives a signal, it goes ahead with the cell cycle. In the absence of this signal, the cell goes into the G0 phase.