BIO 365R Lecture 7 - Lord Kelvin and the transatlantic...

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Unformatted text preview: Lord Kelvin and the transatlantic cable. How does the signal (dots and dashes) attenuate with distance along the cable? The so-called cable equations. (1824-1907) The attenuation of the signal with distance to ~1/3 its value is one space constant ( ). Membrane capacitance and resistance Most biological membranes have a unit capacitance (C M ) of ~1 F/cm 2 . The membrane resistance of biological membranes varies dramatically depending on which channels are open. Membrane resistance can change over a few milliseconds as channels open or close. If an axon were a perfect conductor, current going in one end would come out the other end without attenuation . However, axons are imperfect conductors and current leaks out across the membrane as well a Fowing down the axon. The amount of current that Fows down the axon is related to the ratio between the membrane resistance (r m ) and the internal or axoplasmic resistance (r i ) . That is, r m / r i . r i r m If r i > r m , all of the current would run out across the membrane and the axon would be shorted out. If r m > r i , current will run down the axon but some will leak out along the way. If r m >>>> r i most of the current will run along the axon and little will leak out....
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This note was uploaded on 04/12/2009 for the course BIO 51340 taught by Professor Zakon during the Spring '09 term at University of Texas at Austin.

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BIO 365R Lecture 7 - Lord Kelvin and the transatlantic...

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