Cutaneous facilitation of transmission in reflex pathways from Ib afferents to motoneurones.

Abstract

The effect of volleys in low threshold cutaneous afferents upon transmission of synaptic action from Ib afferents to motoneurons was investigated with intracellular recording from .alpha. motoneurons to [cat] hind limb muscles. There was facilitation from cutaneous afferents of transmission in excitatory and inhibitory reflex pathways from Ib afferents without any evidence for difference in effect on di- and trisynaptic pathways. Volleys in cutaneous afferents probably evoke excitatory action in interneurons of these reflex pathways. The time course of facilitation suggested that cutaneous afferents had disynaptic excitatory connections with the interneurons intercalated in the disynaptic Ib inhibitory pathways to motoneurons. Some observations suggested that interneuronal transmission in Ib inhibitory pathways to motoneurons might be facilitated from Ia afferents. The presumed role of Ib reflex action in regulating muscle tension was discussed.