Spj

Record (post)

Presynaptic Membrane Potential (mV)

FIGURE 13 The relationship between depolarization of the presynaptic terminal and the release of neurotransmitter. (A) Experimental setup; (B) as the presynaptic terminal is depolarized to greater levels, transmitter release (as measured by the amplitude of the postsynaptic potential) increases. Because the results were obtained in the presence of TEA and TTX, these results indicate that the Na+ influx or K+ efflux that occurs during the action potential is not necessary for the release of neurotransmitter. (Modified from Katz B, Miledi R. J Physiol 1967; 192:407-443.)

Presynaptic Membrane Potential (mV)

FIGURE 13 The relationship between depolarization of the presynaptic terminal and the release of neurotransmitter. (A) Experimental setup; (B) as the presynaptic terminal is depolarized to greater levels, transmitter release (as measured by the amplitude of the postsynaptic potential) increases. Because the results were obtained in the presence of TEA and TTX, these results indicate that the Na+ influx or K+ efflux that occurs during the action potential is not necessary for the release of neurotransmitter. (Modified from Katz B, Miledi R. J Physiol 1967; 192:407-443.)

underlie the action potential have no direct effect on the release of chemical transmitter substance from the presynaptic terminal. One merely has to depolarize the cell to get the release of transmitter. Normally, the action potential is essential because it is the vehicle by which the terminal is depolarized. Although changes in Na+ and K+ permeability are important for producing an action potential, the direct influx of Na+ and efflux of K+ are, by themselves, not causally related to the release of the chemical transmitter substance.

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