noun, plural: spindle fibers
Any of a network of filaments that collectively form a mitotic spindle (in mitosis) and meiotic spindle (in meiosis). It is chiefly involved in moving and segregating the chromosomes during nuclear division.
In mitosis, these filaments form at opposite poles of the cell and meet at the equatorial plane. Collectively, they form a spindle-shaped structure, which is widest at the middle then tapers at both ends.
In mitosis, the spindle fibers form during prophase. During metaphase of cell division, the spindle fibers radiate from the centrioles at the opposite poles. Some of them attach to the kinetochores of the chromosomes while others bind to the arms of the chromosomes, still others continue to grow. When the spindle fibers start to pull the chromosomes (via their kinetochores) to opposite poles, this marks the anaphase of cell division.