Critical threshold of noise-induced Ca2+ signal in intracellular Ca2+ system

The detailed bifurcation diagram depending on fixed noise intensity (β = 0.01 μM). Here: regions a and a′ represented the unexcitable regions, meaning that noise could not induce regular Ca2+ signal. Regions b and b′ represented the excitable regions, meaning that noise could induce regular Ca2+ signal. While region c represented the intrinsic Ca2+ signal of the system.