We have shown (Physical Review Letters, 90, 228101 (2003))
that the thermal fluctuations of red blood cells can be accounted for
by a model of a nearly-free, but confined bilayer membrane with a
finite tension; both the confinement and tension  arise from the
coupling of the membrane with the cytoskeleton. Recently, we have
shown that these relatively gentle effects of the
cytoskeleton-membrane couplings on the membrane fluctuations are due
to the dilute nature of the coupling molecules.  To quantify this, we
predict the fluctuation amplitude for a microscopic model of the
inhomogeneous coupling of a fluid membrane and a fixed cytoskeleton.
We find that there is indeed, an effective surface tension and
confinement of such a membrane, in accord with our phenomenological
model, and relate these quantities to the strength and periodicity of
the microscopic coupling.  Finally we address the role of ATP activity
on the cytoskeleton-driven fluctuations and the equilibrium shape of
the cell. We examine in detail the role of spectrin disconnections as
the main ATP-activated network defects on the global cell shape and
membrane fluctuations. Lastly, we relate cytoskeleton defects to
membrane function.