Lecture 3 - Box 7-1 In the 1800s recording"injury...

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Box 7-1
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In the 1800s recording “injury potentials” from a cut muscle showed the inside of a muscle was electrically negative QuickTime p and a TIFF (Uncompressed) decompressor are needed to see this picture. Cut in the muscle
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Bernstein’s hypothesis: resting potential is set by K + Bernstein knew that K + levels inside a muscle are high and Na + levels are low. He hypothesized that nerve and muscles cells are selectively permeable to K + at rest, and that the efflux of K + caused the resting potential. He formalized his hypothesis with the Nernst equation. QuickTime j and a TIFF (Uncompressed) decompressor are needed to see this picture. Julius Bernstein (1839-1917)
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The squid giant axon
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Is the resting potential of the squid giant axon predicted by the Nernst equation? Manipulate extracellular [K + ] o , record membrane voltage (resting potential) with electrode inside axon. Plot of resting potential vs. extracellular [K + ] o (red line). Black line is the predicted resting potential if it were perfectly explained by the Nernst equation for K + ions.
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What if a cell is permeable to more than one ion?
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The Goldman-Hodgkin-Katz equation P = permeability Note: [Cl - ] in and [Cl - ] out are reversed!
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A mammalian neuron has the following intra- and extracellular ion concentrations: Intra (mM) Extra (mM) Na + 10 145 K + 140 5 Ca 2+ 0.0001 2 Cl - 20 110 E k = 58 1 log 5 140 E k = 58(- 1.44) = - 83.5 mV
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The G-H-K equation reduces to this simpler form if we ignore Cl - . Vm = 58log 5 +145(.01) 140 +10(.01) = 58log 6.45 140.1 = - 77.5 mV Membrane is 100x more permeable to K + than Na + Membrane is 50x more permeable to K + than Na + V m = 58log 5 +145(.02) 140 +10(.02) = 58log 7.9 140.2 = - 72.4 mV
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These are the same! V m = 58log 5 +145(.02) 140 +10(.02) = 58log 7.9 140.2 = - 72.4 mV V m = 58log 5(50) +145 140(50) +10 = 395 7010 = - 72.4 mV or
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Is the resting potential of the squid giant axon predicted by the Nernst equation? Manipulate extracellular [K + ] o , record membrane voltage (resting potential) with electrode inside axon. Plot of resting potential vs. extracellular [K + ] o (red line). Black line is the predicted resting potential if it were perfectly explained by the Nernst equation for K + ions.
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How is the ionic gradient created and maintained? There is an excess of anionic charge inside a cell due to net negative charges on nucleic acids & proteins.
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