. Principles of modern biology. Biology. INACTIVE AREA ACTIVE AREA NERVE heart, and these measurements prove helpful in diagnosing cardiac function. Bioelectric Potentials. Each cell, of course, is bounded by a plasma membrane that, in the living state, displays a very distinct electrical polarization. The outer surface is positive in relation to the negatively charged inner surface. In the resting, or unexcited, cell this difference of potential is called the resting potential; it usually amounts to some 50 to 100 millivolts (Fig. 11-3). When a cell is excited, however, a localized and momen-
. Principles of modern biology. Biology. INACTIVE AREA ACTIVE AREA NERVE heart, and these measurements prove helpful in diagnosing cardiac function. Bioelectric Potentials. Each cell, of course, is bounded by a plasma membrane that, in the living state, displays a very distinct electrical polarization. The outer surface is positive in relation to the negatively charged inner surface. In the resting, or unexcited, cell this difference of potential is called the resting potential; it usually amounts to some 50 to 100 millivolts (Fig. 11-3). When a cell is excited, however, a localized and momen- tary depolarization of the membrane occurs and, in fact, there is even a reversal of the normal polarity. This rapid shifting of the membrane potential is called the action po- tential (Fig. 11-3). The action potential is not static, however. It rapidly propagates it- self over the entire cell surface, starting at the point of stimulation. Moreover, the 100 METERS/SECOND. I I I I I I I I I I I I I I I I I I I I I IT l"l"l I I I I I I I I I 5 10 15 ^v 25 MILLISECONDS -Kt-++ +++++++++++ + f—y4+ + + + + + +++ + + + + + + + + cytoplasm—WK:&i;£§^:JM .:3*:ds!££*fSSS-^ MEMBRANE-*-' INSIDE ELECTRODE + + + + + ++ + -rf4>+++ ++ J^--A^-r- + 4 + +B+ + ++ + ++++ ++ OSCILLOSCOPE OUTSIDE ELECTRODE. Please note that these images are extracted from scanned page images that may have been digitally enhanced for readability - coloration and appearance of these illustrations may not perfectly resemble the original Marsland, Douglas, 1899-. New York, Holt, Rinehart and Winston
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