THE COACTIVATION COMMAND FOR ANTAGONIST MUSCLES INVOLVING IB INTERNEURONS IN MAMMALIAN MOTOR CONTROL-SYSTEMS - AN ELECTROPHYSIOLOGICALLY TESTABLE MODEL

The hypothesis of a weighted combination of independent reciprocal (R) and co-activation (C) commands to agonist and antagonist motoneurons (MNs) underlying movement is considered. In contrast to the R command. C command does not influence the equilibrium position of the joint. T his constraint together with experimental data on descending and segme ntal afferent pathways to MNs forms the basis of the neuronal model fo r the C command. In the model, descending systems issue identical sign als to agonist and antagonist MNs. To prevent shifts in the equilibriu m position, these signals are adjusted by interneurons in propriocepti ve pathways compensating the asymmetry of muscle action.