At this point, the chromosomes are still long and thin, and are not visible inside the nucleus. Cells spend most of their life in this non-reproductive phase. The chromosomes coil and shorten, and become visible. It becomes apparent that the chromosomes have duplicated. Pairs of identical chromosomes remain attached to each other at the centromere and each chromosome is called a chromatid.
Chromosomes line up along the center of the cell.
A pair of structures called centrioles form at the poles of the cell, and produce spindle fibers which attach to the centromeres of each chromosome pair. The paired chromosomes split at the centromere and the two halves migrate along the spindle fibers to opposite sides of the cell. At the same time, the center of the cell begins to pinch. Cells return to Interphase and prepare for another round of division. The lifespan of different cell types varies, and some cells such as nerve cells never divide once they are formed.