Der Regelkreis des Kniesehnenreflexes bei der Stabheuschrecke Carausius morosus

In Part B the tendon of the femoral chordotonal organ (receptor tendon) of a fixed leg is sinusoidally moved with different amplitudes and frequencies. This causes movements of the tibia. Figures 1–3 show the amplitudes of the tibia movements and the phase-shifts between tibia-movement and stimulus. As it is known, that a tibia-movement of about 13° corresponds to a movement of the receptor-tendon of 100 m, a bode-plot can be constructed. Figure 4 is the first part of a three-dimensional bode-plot (amplitude ratio) which additionally shows the values of amplitudes and frequencies, at which a phase shift of 180° can be observed. The system is stable, if the gain of the system is smaller than 1 at these values. A gain equal or larger than 1 causes instability. As it can be seen in Fig. 4, the system is stable, but it is not very far from instability. In Part C an inert mass is coupled to the tibia in order to enlarge the phase-shift. After a disturbance, which causes a higher gain of the system, intact legs often show long lasting oscillations of small amplitude (Fig. 6a, b). During these oscillations the other legs are not moved. Sometimes active movements of all legs occur. Active movements of the tested legs have larger amplitudes and are always followed by small-amplitude-oscillations. Legs with cut receptor tendons and intact legs of decerebrated animals never show small-amplitude-oscillations but only active movements. Therefore it is probable that the small-amplitude-oscillations are oscillations of the feedback-system. In Part C 4 another possible explanation for these oscillations is discussed: The forces, produced by the muscles, might be represented by a noise of broad bandwidth from which the mechanical system selects only a small band given by its resonance frequency. In order to test this hypothesis, electrophysiological experiments are done (C5): During slow-amplitude-oscillations of legs with an inert mass added a spike-burst can be observed in the flexor tibiae during extension and in the extensor tibiae during flexion of the femur-tibia-joint. Sometimes no activity in the extensor can be observed. This means, that the activity in the muscles has a phase-shift of about 180° relative to the movement of the tibia: These supports the hypothesis, that the small-amplitude-oscillations are oscillations of the control system of the Kniesehnenreflex. In Part D it is discussed, whether the rocking-movements of the whole animal could be explained by oscillations of control systems. It is, deduced, that if this hypothesis is true, the control system in the coxa-trochanter-joint must be as near to instability as the control system of the Kniesehnenreflex.