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Hodgkin and Huxley developed a set of equations to describe how a cell produces an action potential upon stimulation, through interactions of voltage-dependent Na+ and K+ channels.
When a depolarizing current is injected into a cell, the resultant decrease in the membrane potential activates the voltage-dependent Na+ channels. The activation of the Na+ channels in turn accelerates the depolarization process, producing the rising phase of the action potential. The rise of the membrane potential ultimately triggers the process of Na+ channel inactivation, which prevents further membrane depolarization. At the same time, the voltage-dependent K+ channels are activated, repolarizing the cell and producing the falling phase of the action potential and the afterhyperpolarization.
|The basic equations describing this process are
where Iinj is the injected current.
gNa = gNamax m3h
and the conductance of the K+ channel is governed by a single activation variable n,
gK = gKmax n4
The default parameters are: