b. This ion is largely responsible for maintaining the negative membrane potenti
ID: 186107 • Letter: B
Question
b. This ion is largely responsible for maintaining the negative membrane potential (- 65 mV) of the resting neuron. This ion reaches its equilibrium (same number of ions leaving the cell as there are entering the cell) at a strongly negative membrane potential despite being a positively charged ion. Why? c. If the cell is impermeable to ALL ions except for one ion species, then what will happen to the membrane potential? (i.e., what will it be equal to?) d. The Nernst Equation is This equation tells us the equilibrium potential for a given hAlo ion species if we know the relative concentrations inside vs z,F…1X1 outside the cell miembrane-and assume no movement of other ion species. e. Using the typical ion concentrations present in/out of the giant squid axon, the equilibrium potential for K is 75mV. At rest the cell is-65mV. Why is the resting potential not equal to the equilibrium potential for K? f. The GHK (Goldman, Hodgkin, Katz) Equation describes how all three of the most permeable ion species (K, Na, CI) contribute to the membrane potential. In What doe p etand ter and why it ine io 590 09/59956959 m the equation g How can a cell change p and why is it included for each ion species in the equation?Explanation / Answer
b. If the positively charged ion is present in more concentration inside the cell than outside (caused by active transport) and the cell membrane is permeable to only this ion, it will move outside the cell until equilibrium is reached causing a negative resting membrane potential. Potassium is most likely this positively charged ion to which the cell is permeable and it therefore contributes most to the resting membrane potential
c. The membrane potential will depend on the ion for which the cell membrane is permeable and can be calculated by the Nernst equation.
e. The resting membrane potential is not equal to the equilibrium potential of potassium because the cell membrane is also slightly permeable to sodium and chloride which also contribute to the resting membrane potential. Infact the resting memnrane potential is less negative than if it depended completely on potassium.
f. The term p is the relative permeabilities of the different ions. The relative permeability with the equilibrium potential for the three ion can give the resting membrane potential.
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