Hodgkin and Huxley (HH) were able to reliably measure the voltage- and time-dependent changes in sodium and potassium conductance (gna and gk) during the action potential (Figure 2.11 [Hille]). The story that emerged from such experiments is now part of the core knowledge of all neurophysiologists. After a suprathreshold voltage step, gna quickly rises and falls while gk slowly increases to a steady state (Figure 2.11 [Hille]). In a cell that is not voltage-clamped, this increase in gna causes Vm to rapidly approach Ena. However, the subsequent gk increase, and gna decrease, causes Vm to quickly fall back down to the resting potential near Ek. HH quantified these conductance changes in a model with explanatory and predictive power that only continues to grow. In what follows, I will describe in more detail their model of gk and gna.
Each time I revisit the HH corpus, I am impressed by their profound creativity, technical skills (both quantitative and experimental), and luck.