89:, and a negatively charged membrane, as it is commonly the case in most organisms. The membrane voltage opposes the flow of the potassium ions out of the cell and the ions can leave the interior of the cell only if they have sufficient thermal energy to overcome the energy barrier produced by the negative membrane voltage. However, this biasing effect can be overcome by an opposing concentration gradient if the interior concentration is high enough which favours the potassium ions leaving the cell.
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lowers (makes more negative) the Na equilibrium potential and produces a negative shift in reversal potential. Conversely, increasing the external K concentration raises (makes more positive) the K equilibrium potential and produces a positive shift in reversal potential. A general expression for reversal potential of synaptic events, including for decreases in conductance, has been derived.
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This line of reasoning led to the development of experiments (by Akira
Takeuchi and Noriko Takeuchi in 1960) that demonstrated that acetylcholine-activated ion channels are approximately equally permeable to Na and K ions. The experiment was performed by lowering the external Na concentration, which
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for that ion. This gradient consists of two parts, the difference in the concentration of that ion across the membrane, and the voltage gradient. When these two influences balance each other, the electrochemical gradient for the ion is zero and there is no net flow of the ion through the channel;
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at which the direction of ionic current reverses. At the reversal potential, there is no net flow of ions from one side of the membrane to the other. For channels that are permeable to only a single type of ion, the reversal potential is identical to the
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this also translates to no current across the membrane so long as only one ionic species is involved. The voltage gradient at which this equilibrium is reached is the equilibrium potential for the ion and it can be calculated from the
436:) receptors are nonselective cation channels that pass Na and K in nearly equal proportions, giving the reversal potential close to zero. The inhibitory ionotropic ligand-gated neurotransmitter receptors that carry
365:, or conductance per unit area. Note that the ionic current will be zero if the membrane is impermeable to that ion in question or if the membrane voltage is exactly equal to the equilibrium potential of that ion.
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is equal to 0), the identity of the ions that flow during an EPC can be deduced by comparing the reversal potential of the EPC to the equilibrium potential for various ions. For instance several excitatory
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Brown JE, Muller KJ, Murray G (October 14, 1971). "Reversal potential for an electrophysiological event generated by conductance changes: mathematical analysis".
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Driving force is simply defined as the difference between the actual membrane potential and an ion's equilibrium potential
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refers to the equilibrium potential for a specific ion. Relatedly, the membrane current per unit area due to the type
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receptors, have reversal potentials close to the resting potential (approximately –70 mV) in neurons.
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at which there is no net movement of the ion. The flow of any inorganic ion, such as
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is at the reversal potential for an event such as a synaptic potential (
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590:(4th Enhanced ed.). Jones & Barlet Learning. p. 64-127.
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68:(since membranes are normally impermeable to ions) is driven by the
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An important concept related to the equilibrium potential is the
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We can consider as an example a positively charged ion, such as
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688:. Peter Dayan. Cambridge: MIT Press. pp. 158–160.
554:(6th ed.). Sinauer Associates. pp. 39–106.
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198:ion channel is given by the following equation:
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626:(6th ed.). New York, NY. pp. 615–616.
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700:OCLC
690:ISBN
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