Noise induced excitability is studied in types Ⅰ and Ⅱ Morris–Lecar neurons.Ion channels open and close randomly,creating current fluctuations that can induce spontaneous firing of action potentials.Both noise sources are assumed to be weak so that spontaneous action potentials occur on a longer timescale than ion channel fluctuations.Asymptotic approximations of the stationary density function and most probable are developed to understand the role of channel noise in spontaneous excitability.