Anaphase A depends on motor proteins operating at the kinetochores that, together with the depolymerization of the kinetochore microtubules, pull the daughter chromosomes toward the nearest pole. In anaphase B, the two spindle poles move apart. Two separate forces are thought to be responsible for anaphase B. The elongation and sliding of the overlap microtubules past one another in the central spindle push the two poles apart, and outward forces exerted by the astral microtubules at each spindle pole act to pull the poles away from each other, toward the cell surface.