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. Author manuscript; available in PMC: 2017 Apr 1.
Published in final edited form as: Physica D. 2016 Apr 1;318-319:70–83. doi: 10.1016/j.physd.2015.10.005

Figure 1.

Figure 1

Schematic representation of the model: Turnover of myosin thick filaments: Unbound myosin filaments bind with probability R̄ to the center points of pairs of anti-parallel actin filaments (A1), or, with probabilities R± to the center points of parallel pointed end forward (B1), respectively backward (C1) actin filaments. Myosin forces and F-actin treadmilling have counteracting effects on the position of myosin binding sites as by itself myosin would move towards the barbed ends, while treadmilling moves binding sites towards the pointed ends. A2: Myosin filaments attached to anti-parallel actin filaments shift towards the pointed ends as treadmilling is assumed to exceed actin filament velocities through myosin action. The value ξ represents the relative position of myosin with respect to the centers of actin filaments in a way such that ξ = l/2 corresponds to the pointed ends of actin filaments. A3: Once myosin reaches the pointed ends it detaches and returns to the pool of unbound myosin. B2: Myosin attached to a pair of pointed end-forward actin filaments shifts towards the barbed ends as it can move with its free moving velocity which is faster than F-actin treadmilling. The material velocity of actin filaments moves actin and myosin simultaneously and therefore does not affect their relative position. In the case of parallel actin filaments the relative position ξ = l/2 corresponds to the barbed ends of actin filaments. B3: Once myosin reaches the barbed ends, it detaches. C2, C3: Myosin attached to a pair of pointed end-backward actin filaments moves towards the barbed ends where it detaches. Observe that the material velocity of pointed end backward actin filaments is now written as −υ− as υ− by convention is taken as negative.