C

Example 4.3-2

In a second example, find the conditions whereby two subthreshold area Do input pulses elicit an RPFM SGL output pulse. How far apart in time T can these pulses occur and still give an output pulse at T? The peak amplitude of v(t) when the second pulse occurs is v2pk = Doc(1 + e-cT) 4.3-15

v2pk must equal 9 in the limiting case. Solve for T as in the previous example:

Thus, if the time T between the two pulses exceeds 1.386 ms, there will be no output pulse.

4.3.3 Modeling Adaptation

Given a constant input stimulus, a spiking receptor cell such as the Pacinian corpuscle pressure-sensing neuron in the abdomen will gradually decrease its firing rate to zero. This inability to respond to a steady-state stimulus is called adaptation by neurophysiologists. Adaptation can arise from several causes; it may be due to the primary mechanical structure of the transducer or mechanism, or it may involve time dependence of certain ion channels that give rise to depolarization (Kandel et al., 1991). Functionally, adaptation of a pacinian corpuscle can be modeled by placing a high-pass filter of the form:

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