  Building on the results of our computer simulation (ArXiv cond-mat/0503573)we
develop a theoretical description of the motion of a bead, embedded in a
network of semiflexible polymers, and responding to an applied force. The
theory reveals the existence of an osmotic restoring force, generated by the
piling up of filaments in front of the moving bead and first deduced through
computer simulations. The theory predicts that the bead displacement scales
like x ~ t^alfa with time, with alfa=0.5 in an intermediate- and alfa=1 in a
long-time regime. It also predicts that the compliance varies with
concentration like c^(-4/3) in agreement with experiment.
