During mitosis, mitotic spindle segregates genetic material into two identical daughter cells. Kinetochore microtubules in the mitotic spindle connect the chromosomes to the spindle poles and generate forces on the chromosomes via protein complexes called kinetochores. Measurements have shown that bridging microtubules are stably bound to kinetochore microtubules and in this thesis we developed physical models that clarify their role during cell division. In addition to kinetochore microtubules, bridging microtubules and kinetochores, the model includes the interaction of microtubules with the poles of the mitotic spindle and passive and active molecular motors that laterally connect kinetochore and bridging microtubules and enable their sliding and active motors that regulate dynamics of the microtubule plus ends. For the case of a system that is in metaphase, the model solutions show that active motors at the plus ends of microtubules regulate the transition of microtubules from the growing phase to the shrinking phase and thus limit the movement of kinetochores to the central third of the mitotic spindle. The model predicts that the stochastic contribution in the model provides robustness in the motion of the kinetochore for a wide range of parameters. Also, for the case of a metaphase spindle, that contains bridging microtubules, the model predicts that the kinetochores away from the center of the spindle will achieve a new stable position that correlates with the position of the bridging microtubules overlap. For the case of a system describing the mitotic spindle in anaphase, we have shown that lateral sliding between bridging and kinetochore microtubules generated by active motors located in the antiparallel microtubule bundles allows robust chromosome separation independent of forces generated at the spindle pole.