Fig 5. Phase space perspective of SD.

Panel (a) shows the evolution of slow variables. ΔN^K takes extremum values at de– and repolarization. It is used as a bifurcation parameter to derive the fixed point structures in panel (b) that guide the trajectory in phase space. $\Delta N_g^K$ contributes to ΔN^K and its evolution is also shown. The values at the two points of interest are indicated by colored X markers. The values are used to compute the fixed point structures that guide the dynamics near the de– and repolarization point in (b), respectively.