Coactivation of leg reflexes in the stick insect
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Each leg of a standing stick insect acts as a height controller. The leg contains several joints. Most of these joints are known to be controlled by feedback loops which are the basis of resistance reflexes (review Bässler 1983). This leads to the question of whether the resistance reflex of the whole leg can be understood as a simple, vectorial sum of the individual reflexes provided by the different joints, or whether additional properties emerge by simultaneous stimulation of several joints. Force measurements were performed while passively moving the middle leg tarsus of a fixed stick insect (Carausius morosus) stepwise to different positions. From the dynamic and static forces the torques developed by each joint were calculated. They were compared with the torques developed when only a single joint was moved by the same amount. The comparison shows that for a large range of positions there are no differences between both situations. Differences occur in two cases. First, the muscle system controlling the coxa-trochanter joint seems to be more strongly excited when the entire leg is moved than when only the one joint is moved. This change increases the linearity of the whole system for small deviations from the zero position. Second, the torque developed by the extensor tibiae system for negative steps (corresponding to increased body height), and the levator of coxa and trochanter for positive steps, decreases rather than increases when the whole leg is moved to extreme positions. This contributes to a decrease in the slope of the force-height characteristic and thus to a more non-linear behaviour of the whole system for the extreme positions. It is well known that the amplification factors of resistance reflexes in the leg show a large variation (Bässler 1972a; Kittmann 1991). Our results indicate that any change of the amplification factor influences the reflexes in all leg joints in the same way.
KeywordsTorque Amplification Factor Extreme Position Muscle System Stick Insect
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- Bässler U (1965) Proprioreceptoren am Subcoxal- und Femur-Tibia-Gelenk der Stabheuschrecke und ihre Rolle bei der Wahrnehmung der Schwerkraftrichtung. Kybernetik 2:168–193Google Scholar
- Bässler U (1983) Neural basis of elementary behavior in stick insects. Springer, Berlin Heidelberg New YorkGoogle Scholar
- Clarac F (1977) Motor coordination in crustacean limbs. In: Hoyle G (ed) Identified neurons and behavior of arthropods. Plenum Press, New York pp 167–186Google Scholar
- Dautenhahn K, Cruse H (1990) Resistance reflexes in the leg of an insect: is the whole more than the sum of its parts? In: Elsner N, Roth G (eds) Brain-perception-cognition Proceed. of the 18th Göttingen Neurobiology conference, 55, Thieme, Stuttgart New YorkGoogle Scholar
- Graham D (1985) Influence of coxa-thorax joint receptors on retractor motor-output during walking inCarausius morosus. J Exp Biol 114:131–139Google Scholar
- Kittman R (1991) Gain control in the femur-tibia feedback system of the stick insect. J Exp Biol, 157:503–522Google Scholar
- Schmitz J (1985) Control of the leg joints in the stick insects: differences in the reflex properties between the standing and the walking states. In: Gewecke M, Wendler G (eds) Insect locomotion. Parey, Berlin Hamburg 1985 pp 27–32Google Scholar
- Wendler G (1972) Körperhaltung bei der Stabheuschrecke: ihre Beziehung zur Schwereorientierung und Mechanismen ihrer Regelung. Verh Dtsch Zool Ges 65:214–219Google Scholar