The Fitzhugh Nagumo model is a two-dimensional simplification of the Hodgkin-Huxley model of spike generation in squid giant axons. This system was suggested by FitzHugh (FitzHugh R. : Impulses and physiological states in theoretical models of nerve membrane. Biophysical J. 1:445-466), who called it “Bonhoeffer-van der Pol model”, and the equivalent circuit by Nagumo et al. (Nagumo J., Arimoto S., and Yoshizawa S.  An active pulse transmission line simulating nerve axon. Proc IRE. 50:2061–2070.1962).
This version corresponds to the one described in FitzHugh R. : Mathematical models of excitation and propagation in nerve. Chapter 1 (pp. 1–85 in H.P. Schwan, ed. Biological Engineering, McGraw–Hill Book Co., N.Y.).
See http://www.opensourcebrain.org/projects/fitzhugh-nagumo-fitzhugh-1969 for more details.