During prometaphase, the mitotic spindle is formed conclusively; it ensures movement of condensed chromosomes to the equatorial cell plane and, after that, toward the poles. The spindle framework is a structured system of microtubules, which arises from the cytocenter like in the interphase cell. A pair of centrioles make up one of the two spindle poles. You may also distinguish that the microtubules arise from the only centriole (mother centriole). Polar microtubules are directed from one pole to the other. They are not attached to chromosomes but serve as guides of chromosome movement toward the equator. Kinetochore microtubules are connected with chromosomal centromeres (kinetochore) and move them to the equator. In the image, there is a part of the spindle consisting notably of polar and kinetochore microtubules. A third type of microtubules is called astral microtubules; they are less visible. They are oriented between the centrosome and the cell membrane and help to stretch the poles, to bring them closer to the plasma membrane during chromosome migration in anaphase.