Lecture 7 - Lord Kelvin and the transatlantic cable....

Info iconThis preview shows pages 1–9. Sign up to view the full content.

View Full Document Right Arrow Icon
Background image of page 1

Info iconThis preview has intentionally blurred sections. Sign up to view the full version.

View Full DocumentRight Arrow Icon
Background image of page 2
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) QuickTime · and a TIFF (Uncompressed) decompressor are needed to see this picture.
Background image of page 3

Info iconThis preview has intentionally blurred sections. Sign up to view the full version.

View Full DocumentRight Arrow Icon
The attenuation of the signal with distance to ~1/3 its value is one space constant ( λ ).
Background image of page 4
Membrane capacitance and resistance Most biological membranes have a unit capacitance (C M ) of ~1 μ 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.
Background image of page 5

Info iconThis preview has intentionally blurred sections. Sign up to view the full version.

View Full DocumentRight Arrow Icon
If an axon were a perfect conductor, current going in one end would come out the other end without attenuation .
Background image of page 6
However, axons are imperfect conductors and current leaks out across the membrane as well a flowing down the axon. The amount of current that flows 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
Background image of page 7

Info iconThis preview has intentionally blurred sections. Sign up to view the full version.

View Full DocumentRight Arrow Icon
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. r
Background image of page 8
Image of page 9
This is the end of the preview. Sign up to access the rest of the document.

This note was uploaded on 07/31/2009 for the course BIO 365R taught by Professor Draper during the Spring '08 term at University of Texas at Austin.

Page1 / 29

Lecture 7 - Lord Kelvin and the transatlantic cable....

This preview shows document pages 1 - 9. Sign up to view the full document.

View Full Document Right Arrow Icon
Ask a homework question - tutors are online