Figure 3.

(a) The protrusive force F_a(h) (solid line, and see Eq. 1) in a cylindrical protrusion has the same dependence on height h as the polymerization rate A(h) (inset). (Dotted line) Restoring force due to the myosin motors F_ma ∝ h (Eq. 6); (dashed line) constant restoring force of the membrane F_md (Eq. 4). The stable (unstable) steady-state solutions (solid (shaded) circles). Note that the restoring force of the membrane does not provide a stable solution in this case. (b) The steady-state height of the cylindrical protrusion as a function of the tip complex radius R_tip or the cytoplasm viscosity γ_c (Eq. 10). The two line types (solid and dashed) correspond to two different functions of A(h), as shown (see inset).