The action of knee joint afferents and the concomitant influence of cutaneous (sural) afferents on the discharge of triceps surae gamma‐motoneurones in the cat

Electrical stimulation of group II joint afferents of the posterior articular 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 these responses were consistent with mediation via segmental oligosynaptic spinal pathways. In addition, a longer‐latency facilitation was frequently 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 inhibition or long‐latency facilitation. Brief mechanical indentation of the 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 segmental inputs from group II articular afferents arising in the knee joint. Cutaneous afferents from the sural field exert a selective inhibitory influence over the facilitation of fusimotor discharge by articular afferents.