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, am is small and bm 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 ah is large and bh is small. Thus the h-particles are in the non-inactivating position, outside the membrane. Depolarization increases am and bh and decreases bm and ah. 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 am, bm, ah, and bh to sudden depolarization and repolarization. (C) The response of m, h, m3, and m3h to a sudden depolarization and repolarization. Note that according to Equation 4.20, GNa is proportional to m3h.