We investigate the dynamical chiral symmetry breaking and its restoration at
finite density and temperature within the two-flavor Nambu-Jona-Lasinio model,
and mainly focus on the critical behaviors near the critical end point (CEP)
and tricritical point (TCP) of quantum chromodynamics. The multi-solution
region of the Nambu and Wigner ones is determined in the phase diagram for the
massive and massless current quark, respectively. We use the various
susceptibilities to locate the CEP/TCP and then extract the critical exponents
near them. Our calculations reveal that the various susceptibilities share the
same critical behaviors for the physical current quark mass, while they show
different features in the chiral limit
