Figure 8. Bursting activities associated with dendritic Ca²⁺ spike in a more biophysically realistic model.

(a) Schematic of the biophysically realistic model is shown in the top-right panel. The apical input is , and somatic input is . Left panels show the sample responses recorded in its soma. Somatic voltage V_S, dendritic voltage V_D, internal current I_DS, dendritic Ca²⁺ current I_Ca, and instantaneous firing rate f_inst are plotted against time. The bottom-right close-up shows that the Ca²⁺ conductance is activated when dendritic voltage V_D exceeds a threshold value. (b) Close-up of somatic voltage V_S, K⁺ activation variable w, and firing rate f_inst. Bottom panel shows the close-up of V_S trajectory in space. Five color lines indicate the times at which the nullclines are calculated. (c) Two-dimensional phase portraits in plane. The V_S- and w-nullclines are respectively calculated at time point t₁ −t₅ indicated by colored lines in (b). Blue dotted line represents w-nullcline, and the inverted N-shape lines are the V_S-nullcline at corresponding time point. Gray solid line is the V_S trajectory, and black arrows indicate its direction. ‘S’ indicates stable fixed point, and ‘U’ indicates unstable fixed point. The maximum conductance of dendritic Ca²⁺ current is .