Model definition. (a) Summary of key model parameters including the rates of motor attachment kA and detachment kD, and the bare stepping rate kM. See text for details. (b) Plan view showing the filaments oriented with their light-shaded [+]-ends towards the center. The arrows denote the external pressure acting on the circular elastic wall. (c) Side view of the same, showing the confining walls perpendicular to the z-axis.