The linear and nonlinear viscoelastic response of networks of cross-linked and bundled cytoskeletal
filaments demonstrates remarkable scaling with both frequency and applied prestress, which helps
elucidate the origins of the viscoelasticity. The frequency dependence of the shear modulus reflects the
underlying single-filament relaxation dynamics for 0:1–10 rad=sec. Moreover, the nonlinear strain
stiffening of such networks exhibits a universal form as a function of prestress; this is quantitatively
explained by the full force-extension relation of single semiflexible filaments.