Monosynaptic Ia pathways and motor behaviour of the cat distal forelimb.

The projection pattern from large muscle spindle afferents (Ia) onto cat alpha-motoneurones innervating the elbow, wrist and digit muscles is correlated with new electromyographical and x-ray kinematic data on the motor behaviour of the forelimb. This correlation suggests that the Ia-synergistic groups may be one substrate to organize movement components mobilized in motor behaviour. This hypothesis is based on the data on the active stabilization of the radio-ulnar joints during the stance phase, on the data on the Ia-organization of a motor nucleus taking part in different motor behaviours and on the results showing how the Ia convergence onto the long digit extensor muscles fits the execution of finely tuned movements at ball joints.