Formulas for x' and y' for the Morris-Lecar system with parameters as in section 2.4 of Fall, et al.  
Iapp may be changed by replacing the final '+ 0' in the first line with '+ Iapp' for whatever value of Iapp you like.

x' is
(2*(-60-x)+8*y*(-84-x)- 4.4*.5*(1+ (exp((x+1.2)/18) - exp(-(x+1.2)/18)) / (exp((x+1.2)/18) + exp(-(x+1.2)/18)))  *(x-120) + 0)/20

y' is
.04 * .5*(exp( (x-2)/(2*30) ) + exp( -(x-2)/(2*30))) *(.5* (1+ (exp((x-2)/30) - exp(-(x-2)/30)) / (exp((x-2)/30) + exp(-(x-2)/30))) -y)