图 1. 向量场、确定性轨线和随机轨线. 棕色和粉红色曲线分别表示$v$零倾线和$w$零倾线, SN为不动点, 绿色曲线是确定性路径, 红色粗体线指代分界线, 小箭头代表向量场的方向. 一条代表性随机轨道表示为灰色锯齿线, 里面包含一次自发性动作电位

Fig. 1. Vector field, deterministic and stochastic trajectories. Brown and pink curves indicate the $v$-nullcline and $w$-nullcline respectively. SN denotes the fixed point, the green curves show the deterministic paths, the red bold line suggests the ghost separatrix, and the small arrows represent directions of vector field. A representative stochastic trajectory has been denoted by gray zigzag line, containing a spontaneous action potential