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12 Cards in this Set
- Front
- Back
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When charged particles are involved, electrical driving forces become equally effective. TRUE/FALSE
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TRUE. These forces appear as voltage differences(gradients) across cell membranes.
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These forces arise from what?
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Separation of positive and negative charge by the membrane. The membranes inside surface generally has slightly more negative charge in its immediate vicinity, and the outside surface has slightly more positive charge.
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With regard to this electrical force, what is membrane potential?
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As a consequence of the above statement, this creates an electric force(voltage difference) that may be as large as 0.1volt(100mv) attracting positive charge inward and negative charge outward.
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Membrane potential is always expressed as the voltage inside the cell minus the voltage outside the cell. TRUE/FALSE
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TRUE.
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Membrane potential can range from -10mv in an RBC to about -90mv in heart and skeletal muscle. TRUE/FALSE
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TRUE. The magnitude of these forces can be appreciated if we realize that when K+ is 10 times more concentrated on one side of te membrane, its diffusion to the less concentrated side can be stopped by opposing it with a membrane potential of only 60mv.
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How does charge separation responsible for membrane potential arise?
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First, picture or mentally imagine 3 panels or boxes each hooked up to a meter. In the first box, an impermeable membrane separates 2 solutions of K+ and Cl-. The left side is more concentrated than the right. Nothing happens, because the ions cannot permeate the membrane.
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What must occur to change or set in motion the above scenario?
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In the next box or panel, picture, K+ channels are introduced, K+ can get through, but Cl- cannot. K+ begins to diffuse to the right, building up positive charge on the right and abandoning negativr charge on the left.. A voltage gradient is created across the membrane, which tends to move K+ in the opposite direction from left to right.
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Considering what has thus far been explained, how would an equilibrium potential exist?
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In the third box or panel, imagine, as more K+ diffuses, the voltage gradient grows larger until it is just able to balance the concentrated gradient. At this juncture, net K+ movement ceases, and the system is in equilibrium. The voltage gradient required to stop the diffusion of any ion is called its equilibrium potential.
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Similar effects occur in cell membranes, but now we deal with more ions, and the system does not settle down to equilibrium. Explain.
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The Na+-K+ pump establishes a K+ gradient: high K+ on the inside, low on the exterior side
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How does Na+ fit into the above statement?
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It also establishes an oppositely directed Na+ gradient, but this is not as important because there are many more operative K+ channels to establish a voltage gradient(membrane potential) with the inside negative. The magnitude of the membrane potential is not quite equal to the K+ equilibrium potential. Other ions may permeate the membrane, besides K+.
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Each time the pump cycles, 3 Na+ move out, but only 2 move in, this results in a net movement of one positive charge out. TRUE/FALSE
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TRUE.
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Are the concentrations of Na+ and K+ fairly constant?
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Yes, but they are not in equilibrium. They settle down to steady values because as fast as they leak in or out, they get pumped back out or in.
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