Springer Online Journal Archives 1860-2000
Summary 1. The coxo-trochanteral joint of the locust hindleg is supplied with five mechanoreceptive sense organs: A hairplate (HP) and a row of hairs (RH), two strand receptors (SR1, SR2) and a muscle receptor organ (MRO) (BrÄunig 1982). We report here an investigation of these mechanoreceptors with regard to their afferent responses to static and dynamic mechanical stimulation. 2. The only receptor suited for continuous measurement of joint position is the HP: its units are active over the entire range of possible joint positions and their number increases in proportion to the degree of joint levation (Fig. 3). The RH complements the HP as an additional sensor for extreme levation (Fig. 4). 3. Both SR are sensitive to the dynamic phase of joint depressions. Units of the multicellular SR1 respond over the entire range of joint movements, the single unit of SR2 is tuned to the lower half of that range (Fig. 5). 4. The sensory cell of the MRO is activated when the organ is stretched during depression of the joint (Fig. 6). Increasing slack of the organ during levation is compensated by activation of its receptor muscle. The MRO motor neuron is progressively excited with increasing joint levation, mainly by HP and RH (Figs. 6, 7, 8). 5. During stimulation of internal mechanoreceptors (SR1, SR2, and the sensory cell of the MRO) and during spontaneous motor activity the MRO motor neuron is co-activated with levator motor neurons (Figs. 9, 10). This mechanism may help to compensate for slack before the reflexes from HP and RH set in (see 4.). 6. The motor neuron of the MRO receptor muscle is not only activated by sense organs of the coxo-trochanteral joint, but also by proprioceptors of neighboring joints (Fig. 11). 7. Since all coxo-trochanteral joint receptors exert reflexes on motor neurons of power muscles and the efferent unit of the MRO, manipulation and extirpation of any one receptor must result in direct effects on the motor output of the metathoracic ganglion, but also additional indirect effects due to altered operation of the MRO.
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