  In an extension of the Nambu-Jona-Lasinio model where the quarks interact
with the temporal gluon field, represented by the Polyakov loop, we explore the
relation between the deconfinement and chiral phase transitions. The effect of
Polyakov loop dynamics on thermodynamic quantities, on the phase structure at
finite temperature and baryon density and on various susceptibilities is
presented. Particular emphasis is put on the behavior and properties of the
fluctuations of the (approximate) order parameters and their dependence on
temperature and net--quark number density. We also discuss how the phase
structure of the model is influenced by the coupling of the quarks to the
Polyakov loop.
