  We discuss the implementation of a multiscale biophysico-chemical model able
to cope with the main mechanisms underlying cumulative exocytosis in cells. The
model is based on a diffusion equation in the presence of external forces that
links calcium signaling and the biochemistry associated to the activity of
cytoskeletal-based protein motors. This multiscale model offers an excellent
quantitative spatio-temporal description of the cumulative exocytosis measured
by means of fluorescence experiments. We also review pre-existing models
reported in the literature on calcium waves, protein motor activation and
dynamics, and intracellular directed transport of vesicles. As an example of
the proposed model, we analyze the formation of the shield against polyspermy
in the early events of fertilization in sea urchin eggs.
