**Fig. 4.16.** The process, in the Hodgkin-Huxley model, determining the variation of sodium conductance with depolarization and repolarization with voltage clamp.

(A) Movement of m- and h-particles as a response to sudden depolarization. Initially, a_{m} is small and b_{m} is large, as indicated by the thickness of the arrows. Therefore, the fraction of particles of type *m* in the permissive state (inside the membrane) is small. Initially also the value of a_{h} is large and b_{h} is small. Thus the h-particles are in the non-inactivating position, outside the membrane. Depolarization increases a_{m} and b_{h} and decreases b_{m} and a_{h}. Thus the number of m-particles inside the membrane, *m*, rises exponentially toward unity, and the number of h-particles outside the membrane, h, decreases exponentially toward zero.

(B) The response of transfer rate coefficients a_{m}, b_{m}, a_{h}, and b_{h} to sudden depolarization and repolarization. (C) The response of *m*, *h*, *m*^{3}, and *m*^{3}h to a sudden depolarization and repolarization. Note that according to Equation 4.20, *G*_{Na} is proportional to *m*^{3}h.