sentence: The unbound myosin is assumed to diffuse rapidly on the length scale of the filopodium and , on the time scale of filopodial dynamics , to be in equilibrium with the large reservoir contained in the adjacent dendrite ; therefore its concentration , m , is assumed to be constant.Bound myosin moves with the F-actin at the velocity v ( x) and can also diffuse due to random motion of the actin filaments ( Kruse et al ., 2004 ) .