Reduced HH

$$F(v,w) = g_Kw^4(v-v_K) +g_{Na}m_\infty^3(v)(0.8-w)(v-v_{Na})$$

$$+ g_l(v-v_l)$$ (14)

$$G(v,w) = \alpha_w(v)(1-h)-\beta_w(v)w$$ (15)

where

$$\alpha_w = 0.01{10-v\over \exp({10-v\over 10})-1},\qquad \beta_w = 0.125\exp({-v\over 80})$$ (16)

Typical parameter values are $g_{Na} = 120$, $g_k = 36$, $g_l = 0.3$, $v_{Na} = 115$, $v_K = -12$, and $v_l = -10.5988$. The high precision of $V_l$ is to insure that $v=0$ is the rest state.
Phase portrait:

To see a derivation of this model, click here .