Equivalent Circuit of an Axon Membrane

Hodgkin & Huxley’s voltage clamp of the squid giant axon

Feedback Amplifier current proportional to

difference (E-input)

Input SignalMeasured

Current

Measured voltage

Hodgkin & Huxley’s voltage clamp of the squid giant axon:Current response to hyper-polarization and de-polarization

early inward Na

late outward K

Hodgkin & Huxley’s voltage clamp of the squid giant axon:Current response to hyper-polarization and de-polarization

late outward K

early Na

Hodgkin & Huxley separation of Na and K currents by variation of bath Na concentration

Separation of Na and K Current-Voltage curves

Separation of Na and K Ionic conductance changes

Rapid changes in gNa

Slow changes in gK

Na and K conductance at various voltage clamp steps

Channel openings and closings during Action Potential

Example of time course of changes in n & n^4 ~ gK and m, h & m^3*h ~ gNa

Voltage dependence of Hodgkin-Huxley model parameters