29cap - 9/29/09 -Everything so far: surface membrane...

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9/29/09 -Everything so far: surface membrane phenomena (except 2 nd messengers) -sodium channels: once you turn them on they turn off after a certain period of time -partial potentials -ratio for sodium across cell membrane: 10:1 or 100:1 (external:internal) -ratio for calcium: external: 10^-3, internal: 10^-7 (1000 100,000:1) and remember that calcium’s valence is ++ -so every calcium that comes in has twice as much effect as sodium coming into membrane -cardiac muscle: use calcium! Pg 296 (notice that calcium action potentials are very long), shape is different -permeability: delayed turn on of calcium permeability, then potassium permeability remains fairly high, then turns off about the time that calcium permeability turns on, turns on when calcium is turning off -which channels evolved first? --- -some nerve cells: ends of axon can be very far away from cell body (even up to meters!); 1-10 microns in diameter -takes about 30-40 min to diffuse (pure diffusion) in an axon that is meters long
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29cap - 9/29/09 -Everything so far: surface membrane...

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