At the checkpoint, it is determined if the sister chromatids are properly attached to the spindle fibers.

During at the near end of the metaphase stage of mitosis, a M Checkpoint occurs to determine if all sister chromatids (two stands of chromatids) are correctly attached or joined together to the spindle fibers that happens at the centromere.

It is called the medulla oblongata or people usually call it medulla. it is the lower half of the brain stem continuous with the spinal cord.