INHIBITORY PROJECTIONS FROM PRONATOR TERES TO BICEPS BRACHII MOTONEURONS IN HUMAN

Neural projections from the pronator teres (PT) muscle to biceps brach ii (BB) motoneurones were studied in three healthy human subjects usin g a post-stimulus time histogram method. In 25 BB motor units, electri cal stimulation to the PT nerve with intramuscular needle electrodes i nduced inhibition in nine units (36%), whereas facilitation was produc ed in 18 units (72%) by stimulation to the median nerve trunk with sur face electrodes at the distal end of the intermuscular septum of the a nn or in the cubital fossa. Six motor units (24%) received both inhibi tion (PT nerve stimulation) and facilitation (median nerve trunk stimu lation). In the six, the latency of the inhibition was, on average, 1. 2 ms longer than that of the facilitation. The stimulation site for th e inhibition was, on average, 4.8 cm distal to that for the facilitati on. The inhibition was evoked with an intensity well below the motor t hreshold. These findings suggest that BE motoneurones receive oligosyn aptic inhibition of group I afferents from PT in human.