Systems Biomechanics of the Cell - Systems Biomechanics of the Cell - page 46

Fig. 26 Typical trajectories of centrosomes oscillating within a synaptic area. Coordinates as in
Fig. 25 . Note x - y phase shift leading to gyrations, and apparent beats. Reproduced from Kim and
Maly ( 2009 ) under the Creative Commons Attribution License
systematic changes over at least 1 h of simulated physical time. Typically it appears
that there are overlapping and interfering periodic motions. Also, oscillatory move-
ments that are mostly tangential to the model cell-cell interface occur simultane-
ously with oscillatory movements that are orthogonal to it. Gyrations (looping
motions parallel to the interface) can also be discerned in the complex trajectory of
the model centrosome (Fig. 26 ).
Considering the origin of the oscillations and of the repeated overshooting
exhibited by the centrosome, it is important to point out that inertia plays no role in
intracellular movements due to the prevailing near-zero Reynolds number con-
ditions. In fact, like in models for comparable types of intracellular movements
(e.g., Cytrynbaum et al. 2003 ; Grill et al. 2005 ; Kozlowski et al. 2007 ), there is no
mass in the Kim-Maly model. Also, the model is strictly deterministic, and there-
fore the deflections from the middle position of the centrosome are not due to
molecular stochasticity.
Close inspection of the model predictions reveals that when the centrosome
passes the middle point during oscillations, the microtubule aster shows significant