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Ordinarily the response of the synapse to an impulse is the production of
a relatively large EPP (end plate potential). To get at smaller potentials
one lowers the calcium concentration and adds magnesium to the muscle bath.
This effectively inhibits the response, allowing for study of small responses.
The animation above illustrates what one observes: instead of a continuum
of possible potential responses, each response seems to be a multiple of a
certain miniature EPP (MEPP) of around 0.4 mv (millivolts). To better
understand the nature of these "quantal" responses one employs statistical
analysis. ("Quantal" means discrete, noncontinuous, like the counting numbers - in particular, this does not indicate any tie to quantum mechanics, so don't panic - it's a simple concept. That is, each response will be a summation of 0, 1, 2, 3, 4 or more MEPPs. The animation above illustrates 0, 1, 2 and 3 MEPP responses. The horizontal axis is time; the verticle axis is potential, with the horizontal lines representing 1, 2 and 3 MEPPs.) |