An electronic analog that models the burst generating neuronR15of theAplysiaabdominal ganglion is described. The analog is based on the four branch Hodgkin-Huxley equivalent circuit for a patch of squid axon membrane, with a choice of parameter values appropriate to theAplysiacell membrane. To realize the slow subthreshold oscillations seen in cellR15upon exposure to the drug tetrodotoxin (TTX), it was necessary to include two additional conductance branches,g′Naandg′K, to the basic Hodgkin-Huxley circuit. Without these, the analog was capable of generating only action potentials and hence termed the “suprathreshold” analog. With all six branches operative, bursts very similar to those seen inR15were realized, and subsequent inhibition of the Hodgkin-Huxley sodium conductancegNaresulted in the desired subthreshold oscillations. The electronic circuitry and the performance of the “suprathreshold” and complete analog are described. An explanation is offered for the progressive widening of the action potentials within a burst seen inR15. The analog also simulates the phenomenon of potassium ion accumulation outside the cell membrane during a burst, using a local feedback loop to reduce the potassium equilibrium potential in a manner roughly proportional to the logarithm of the time integral of the outward potassium current. Some consequences of this effect are als
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