Fig. 6.

The graph of derivative and phase planes of (5) with 3 sets of parameters. A: The time derivative of voltage is always positive and the cell without M-current has a natural frequency of 34 Hz ($g_M=0$ mS/cm², $I_{\mathit{app}}=0.68$ μA/cm², $a=0$). B: The phase plane of the cell with M-current. The cell is firing at 34 Hz without external inputs ($g_M=1.5$ mS/cm², $I_{\mathit{app}}=9.1$ μA/cm², $a=0$). C: The same cell as in B but with 32 Hz external pulses. The voltage resets to a higher point near the V-nullcline than in B ($g_M=1.5$ mS/cm², $I_{\mathit{app}}=9.1$ μA/cm², $a=0.6$)