A Locomotor-Related “Autogenetic” Ib Excitation of Hind-Limb Extensor Muscles in the Cat

Abstract

In this Chapter we review our findings that stimulation of group I afferents from ankle and knee extensor muscles may reset and/or entrain the intrinsic spinal rhythm of “fictive” locomotion in the cat; these afferents are thus acting on the motoneurones through the spinal rhythm generators. A train of group I volleys delivered during a flexor burst would abruptly terminate the flexor activity and initiate an extensor burst. The same stimulus given during an extensor burst prolonged the extensor activity, while delaying the appearance of the following flexor burst. It has been shown that the major part of these effects originates from Golgi tendon organ Ib afferents. Intracellular recordings from extensor motoneurones during locomotion revealed that stimulation of group I afferents produces oligosynaptic excitation in this situation, rather than the “classical” Ib inhibition. We also discuss the possible functions of this proprioceptive control as well as the present understanding of the organization of the rhythm generator for locomotion in the cat.