THE ACTION OF KNEE-JOINT AFFERENTS AND THE CONCOMITANT INFLUENCE OF CUTANEOUS (SURAL) AFFERENTS ON THE DISCHARGE OF TRICEPS SURAE GAMMA-MOTONEURONS IN THE CAT

Electrical stimulation of group II joint afferents of the posterior ar ticular nerve (PAN) to the knee evoked short-latency facilitation and/ or inhibition of the background discharge of gastrocnemius-soleus (GS) gamma-motoneurones in decerebrated spinal cats. The latencies of thes e responses were consistent with mediation via segmental oligosynaptic spinal pathways. In addition, a longer-latency facilitation was frequ ently observed. Mechanical non-noxious stimulation of the skin within the field of innervation of the sural nerve, on the lateral aspect of the heel, suppressed the short-latency facilitation, but not the inhib ition or long-latency facilitation. Brief mechanical indentation of th e posterior aspect of the knee joint capsule could elicit facilitation or inhibition of gamma-motoneurones. Facilitation, but not inhibition , was blocked by anaesthesia or section of the PAN. Both actions could be suppressed by mechanical stimulation of the heel. We conclude that GS gamma-motoneurones receive both facilitatory and inhibitory segmen tal inputs from group II articular afferents arising in the knee joint . Cutaneous afferents from the sural field exert a selective inhibitor y influence over the facilitation of fusimotor discharge by articular afferents.