Fig. 4

Bifurcation Diagrams of Full AP Systems. The red dashed lines show the maximum and minimum voltage values of the unstable limit cycles of the full AP systems that were detected, the red solid lines correspond to stable limit cycles. In PP), PV), UP), the blue markers depict the beginning of a cascade of period doubling bifurcations of stable limit cycles, in PPz), PVz), UPz) the blue markers show the PD bifurcations of a particular cascade in close vicinity to the G _K value resulting in the chaotic EAD dynamics of Fig. 1. PP) Bifurcation diagram of model PP with the potassium conductance G _K as continuation parameter (I _sti chosen as for Fig. 1PP). PV) Bifurcation diagram of model PV with the potassium conductance G _K as continuation parameter (I _sti chosen as for Fig. 1PV). UP) Bifurcation diagram of model UP with the potassium conductance G _K as continuation parameter. The solid and dashed black lines denote stable and unstable fixed points of model PP. At the supercritical Hopf bifurcation, stable limit cycles of small amplitudes emerge that go through a cascade of PD bifurcations, depicted by the blue markers, before they turn into limit cycles of large amplitudes that correspond to periodic EAD dynamics. In between lies an area that features both periodic and chaotic dynamics, including chaotic EAD dynamics as shown in Fig. 1UP. PPz) Zoom into the PD area of PP), PVz) zoom into the PD area of PV), and UPz) zoom into the PD area of UP), all in neighborhood of the G _K values corresponding to the chaotic EAD traces shown in Figures 1PP-1UP. This suggests that the PD points numerically detected are part of an infinite PD cascade leading to chaotic EADs