  We study the transient regime of type-II biophysical neuron models and
determine the scaling behavior of relaxation times $\tau$ near but below the
repetitive firing critical current, $\tau \simeq C (I_c-I)^{-\Delta}$. For both
the Hodgkin-Huxley and Morris-Lecar models we find that the critical exponent
is independent of the numerical integration time step and that both systems
belong to the same universality class, with $\Delta = 1/2$. For appropriately
chosen parameters, the FitzHugh-Nagumo model presents the same generic
transient behavior, but the critical region is significantly smaller. We
propose an experiment that may reveal nontrivial critical exponents in the
squid axon.
