Bifurcation diagrams and time simulations of bursting. Each panel is made with a simplified Chay–Keizer model (Tsaneva-Atanasova et al., 2010). Bifurcation diagrams with overlaid burst trajectories (blue) in upper subpanel. Solid lines, stable solutions; dashed lines, unstable equilibria; dotted line, unstable oscillations. (A) Pure square wave without spikes. (B) β cell–like square-wave bursting. (C) Pituitary-like bursting. (D) Bursting without bistability requires a second slow variable, as in this caricature of bursting in the R15 neuron of Aplysia.