MEMBRANE-POTENTIAL CHANGES OF SKELETOMOTOR NEURONS IN RESPONSE TO RANDOM STRETCHES OF THE TRICEPS SURAE MUSCLES IN DECEREBRATE CATS

The properties of membrane potential changes of skeletomotor neurons ( S, FR, and FF) innervating triceps surae muscles during pseudorandom s tretching of these muscles were studied in decerebrate cats. Peak ampl itudes of pseudorandom muscle stretches ranged from 119 mu m to 4.15 m m peak-to-peak. Sequences of ten identical stretching periods were app lied for averaging. Shapes of membrane potential changes and probabili ty density distribution of amplitudes of the input and output signals and power spectra suggest that the skeletomotor neuron membrane has no nlinear properties. First- and second-order Wiener kernels were determ ined by applying the cross-correlation (Lee-Schetzen) method. The resu lts suggest that the transfer function between muscle stretches and su bthreshold membrane potentials is a Wiener-type cascade. This cascade is consistent with a linear, second-order, underdamped transfer functi on followed by a simple quadratic nonlinearity [linear (L) system foll owed by nonlinear (N) system, or LN cascade] Including the nonlinear c omponent calculated from the second-order Wiener kernel improved the m odel significantly over its linear counterpart, especially in S-type m otoneurons. Qualitatively similar results were obtained with all types of motoneurons studied.