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

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Unformatted text preview: Box 7-1 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 Bernsteins 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) The squid giant axon 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. What if a cell is permeable to more than one ion? The Goldman-Hodgkin-Katz equation P = permeability Note: [Cl- ] in and [Cl- ] out are reversed! 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 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 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 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. 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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Lecture 3 - Box 7-1 In the 1800s recording injury...

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