Discrete dynamic simulation of the Boolean EGF/NRG1 example model (Figure 2B) using synchronous updating. (A) Response to EGF stimulation. The inputs in Figure 2B were set as follows: EGF = 1, NRG1 = 0, ErbB1 = ErbB2 = ErbB3 = 1. (B) Response to EGF stimulation in presence of MEK inhibitor blocking the catalytic site of MEK. The inputs were set as in Figure 4A. In addition, the edge MEK → ERK was removed from the model in Figure 2B.