Читать книгу EEG Signal Processing and Machine Learning - Saeid Sanei - Страница 53

Lewis electronic membrane models are based on the Hodgkin–Huxley equations. All the components are parallel circuits connected between nodes representing the inside and outside of the membrane. He realized the sodium and potassium conductances using electronic hardware in the form of active filters. Since the model output is the transmembrane voltage V _m, the potassium current can be evaluated by multiplying the voltage corresponding to G _K by (V _m − V _K). Figure 3.14 is consequently an accurate physical analogue to the Hodgkin–Huxley expressions, and the behaviour of the output voltage V _m corresponds to that predicted by the Hodgkin–Huxley equations. The electronic circuits in the Lewis neuromime had provision for inserting (and varying) not only such constants as G _{K max}, G _{Na max}, V _K, V _Na, V _Cl, which enter the Hodgkin–Huxley formulation, but also τ_h , τ_m , τ_n , which allow modifications from the Hodgkin–Huxley equations. In this realization the voltages of the biological membrane are multiplied by 100 to fit the electronic circuit. In other quantities, the original values of the biological membrane have been used.