BEHAVIOUR OF CLAW FLEXOR SYSTEM IN STICK INSECT CARAUSIUS MOROSUS BR

1. Optical methods for the recording of the position and movements of the 5 unrestrained distal tarsal segments are described (Figs. 1-3). The position and movements of the tarsal segments allow immediate conclusions regarding the behaviour of the flexor unguinum muscle, since this is the only muscle controlling the joints. 2. Under the influence of walking the tonus in the flexor unguinum muscle of a restrained hind-leg is reduced; at the same time the latency of the reaction to a constant test stimulus is prolonged (Fig. 6, Table 2); both parameters show a diurnal periodicity when such periodicity is evident in the walking activity of the animal (Fig. 8, Table 2). These relationships no longer obtain when the ventral nerve cord of the animal has been severed between the second and the third thoracic ganglion (operated animals, Fig. 8, Table 2). 3. Through various stimuli it is possible to produce a rapid reduction of the tonus and at the same time a transient increase in the latency of reflex responses in the flexor unguinum muscle of the hind-leg of operated animals (Fig. 9). Occasionally such a simultaneous change in both parameters also develops without an external cause. 4. The form of reflex responses and readiness to grasp show endogenous fluctuations and transient changes as after-effects of various stimuli (Fig. 11). In extreme cases the muscle reacts temporarily by relaxing instead of contracting. 5. Two kinds of periodical tarsal movements are described: a) Wagging. Faint movements, 80-120/min, displayed only by undisturbed animals at rest. Wagging can be superimposed on waving movements. b) Waving. Stronger movements, 8-22/min. Afferent signals are probably not required for the pattern characteristic of this movement. Intact animals but rarely manifest waving movements spontaneously. In operated animals waving is much commoner. Towards the onset of waving tonus is usually reduced (Fig. 12) and the latency of reflex movements is increased. Between 90 and 280 muscle potentials appear during a single movement, caused by one (ore possibly more than one) motoneuron not responsible for tonus. Changes of the duration of movements and intervals are mostly, but not always, negatively correlated (Fig. 16). Through a short stimulus applied to the abdomen the waving can be suppressed for 1/4-3 min (Fig. 17); waving probably ceases during walking as well. 6. A short percussion stimulus administered after waving can either shorten or lengthen the interval during these movements (Figs. 18-20). There is no subsequent correction for the phase displacement thus introduced into the waving rhythm. The stimulus can cause a quick response (Fig. 22) which often develops into a waving movement. If the stimulus is given during the waving movement, the latter is usually prolonged; but it can also be terminated prematurely (Fig. 23). Under repeated stimulation the frequency of waving is increased; the waving rhythm can be synchronized with the stimuli if the interval between stimuli is not too short. 7. The following points are discussed: a) how it is possible that the same stimulus can elicit opposite reactions; b) conclusions concerning the control of tarsus movements during walking; c) the similarity of waving to the behaviour of certain neuronal oscillators in crustacea. © 1969 Springer-Verlag.