What happens in the prometaphase of mitosis?

Prometaphase:

1. Prometaphase begins with the sudden fragmentation of the nuclear envelope into numerous tiny vesicles, which are then split among the prospective daughter cells.
2. Breakdown of the nuclear membrane is required for spindle assembly.
3. The microtubules of the developing spindle do not have access to the chromosomes until the nuclear membrane ruptures.
4. Microtubules quickly grow and dissolve as they spread out of centrosomes.
5. As prometaphase progresses, microtubules sprouting from both poles of the spindle pull and tug on chromosomes in opposite directions, until the pole-directed pressures are eventually balanced.
6. Sister chromatids do not separate because they are held together by the cohesin that remains at their centromeres.
7. At the conclusion of prometaphase, chromosomes are bi-oriented, which means that the kinetochores on sister chromatids are attached to opposing poles of the spindle via microtubules.