Tactile sensilla of the trochanteral hair plate in the coxotrochanteral joint of the cockroach leg were stimulated by random (white noise) displacement and the afferent action potentials resulting from the stimulation were observed. From the resulting signals, the first and second order frequency response functions between the stimulus and the response were computed, together with their inverse Fourier transforms, the time domain Wiener kernels. Analysis of these results shows that the behaviour of the receptor may be minimally accounted for by a cascade of two functional elements, where the first is a linear element affected by the past history of the input signal (memory) and the second is a nonlinear element with no memory. The behaviour of the linear element is very close to that of a time differentiator or velocity detector, while the nonlinear element behaves as a rectifier which transmits the velocity signal only during flexion of the limb. The results suggest that the functional description may correspond to a physical system with two parts. The element performing differentiation is probably a fluid cavity in the mechanical connection from the hair to the dendrite, and the element performing rectification is most likely to be found in the cell membrane of the dendrite.
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