Fig 3. Bifurcations in the steady-states of the single cell.

The resting state (V = −1.25) is stable (solid line) for all values of parameter b > 0. A pair of unstable fixed points (dashed lines) emerge via a saddle-node (SN) bifurcation at b = 1.64. The lower branch is the saddle and the upper branch is the node. The node becomes stable via a Hopf bifurcation (HB) at b = 1.76. The stable up-state co-exists with the stable resting state for b ≥ 1.76.