AlphaNa = 0.1 * f(0.1*(VoltageDelta-10.0))
The limit for $x\to 0$ can actually be interpreted as difference quotient, you might also appeal to l'Hopital, to find that $f(x)\to 1$. So if you want to play it safe, you can employ a 3-tier or 4-tier implementation of this function
if abs(x)<1e-12: ...
I'll start with a disclaimer, my PhD is in the fast computation of eigenvalues, my specialty is not in machine learning at all. This is just some stuff I remember from some master level courses. I have two ideas that might work.
Traditional convolutional neural nets are very good at classifying. For example, "does this image contain a dog", ...