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The equilibrium potential for an ion is the membrane potential at which there is no net movement of the ion. [1] [2] [3] The flow of any inorganic ion, such as Na + or K +, through an ion channel (since membranes are normally impermeable to ions) is driven by the electrochemical gradient for that ion.
A current with a reversal potential below threshold, such as a typical K + current, is considered inhibitory. A current with a reversal potential above the resting potential, but below threshold, will not by itself elicit action potentials, but will produce subthreshold membrane potential oscillations.
The reversal potential is shown to be contained in the GHK flux equation (Flax 2008). The proof is replicated from the reference (Flax 2008) here. We wish to show that when the flux is zero, the transmembrane potential is not zero.
Thus, to get current density from molar flux one needs to multiply by Faraday's constant F (Coulombs/mol). F will then cancel from the equation below. Since the valence has already been accounted for above, the charge q A of each ion in the equation above, therefore, should be interpreted as +1 or -1 depending on the polarity of the ion.
and the current through a given ion channel is the product of that channel's conductance and the driving potential for the specific ion = where is the reversal potential of the specific ion channel. Thus, for a cell with sodium and potassium channels, the total current through the membrane is given by:
In electrophysiology, the threshold potential is the critical level to which a membrane potential must be depolarized to initiate an action potential. In neuroscience , threshold potentials are necessary to regulate and propagate signaling in both the central nervous system (CNS) and the peripheral nervous system (PNS).
Afterhyperpolarization, or AHP, is the hyperpolarizing phase of a neuron's action potential where the cell's membrane potential falls below the normal resting potential. This is also commonly referred to as an action potential's undershoot phase. AHPs have been segregated into "fast", "medium", and "slow" components that appear to have distinct ...
Rheobase is a measure of membrane potential excitability. In neuroscience, rheobase is the minimal current amplitude of infinite duration that results in the depolarization threshold of the cell membranes being reached, such as an action potential or the contraction of a muscle. [1]