Four main proprioceptors monitor tibial position in the hindleg of the locust: the femoral chordotonal organ (FCO), the lump receptor, the suspensory ligament receptors and Brunner's organ. The influence of these proprioceptors on quantitative aspects of the kick motor programme has been investigated. The parameters measured were the duration of the initial flexion burst, the duration of co-activation of flexor and fast extensor tibiae (FETi) motoneurones, the number of FETi spikes during the co-activation, the interval between the kick and post-kick flexion, the number of FETi spikes occurring in this interval and the duration of post-kick flexion activity. The lump receptor and Brunner's organ have no detectable effect on any of these parameters. The FCO has highly significant effects on the duration of both initial flexion and post-kick flexion bursts, and on the number of FETi spikes occurring after the moment of tibial extension. The suspensory ligament receptors have significant effects upon the number of FETi spikes after the kick and the interval between the kick and the post-kick flexion. However, no proprioceptor had any influence upon the duration of co-activation or the number of FETi spikes during the co-activation. Thus, although elements of the kick motor programme preceding and following co-activation are strongly influenced by proprioceptors monitoring tibial position and movement, the co-activation stage, which is central to the effectiveness of the complete behaviour pattern, is not affected.

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