The Exoskeleton and Insect Proprioception Ii. Reflex Effects of Tibial Campaniform Sensilla in the American Cockroach, Periplaneta Americana

1. Mechanical stimulation of individual tibia! campaniform sensilla produces specific reflex effects upon motoneurones to leg muscles. 2. The reflex effects of a campaniform sensillum depend upon the orientation of its cuticular cap. The proximal sensilla, oriented perpendicular to the long axis of the tibia, excite slow motoneurones to the extensor tibiae and extensor trochanteris muscles and inhibit slow motoneurones to the flexor tibiae and flexor trochanteris muscles. The distal sensilla, oriented parallel to the tibia, exhibit reflexes of opposite sign, inhibiting the extensors and exciting the flexors. 3. These reflexes constitute a negative feedback system. Individual sensilla specifically excite motoneurones which innervate muscles whose resultant tensions decrease the firing of those sensilla. 4. It is postulated that individual campaniform sensilla can detect loading of the leg in various postures and can excite appropriate motoneurones in compensation. These receptors can also detect strains caused by large, resisted contractions of the antagonist muscles and inhibit the corresponding motoneurones.