The mitotic spindle is a structure of the eukaryotic cytoskeleton involved in mitosis and meiosis. It consists of a bundle of microtubules joined at the ends but spread out in the middle, vaguely resembling an American football in shape. The spindle is aligned perpendicularly to the plane along which the cell is to divide. In most cells, the spindle is formed by the centrosomes as they move apart.
Some of the spindle's microtubules attach to the kinetochores that assemble on the centromere portion of the chromosomes and then pull the chromosomes into alignment along the center of the spindle. Once all the chromosomes are aligned with sister chromatids pointing to opposite ends of the spindle, the sister chromatids separate and are dragged away from each other, ensuring that each daughter cell will receive one chromatid after the cells divide in cytokinesis.