SINGLE UNIT RECORDINGS FROM MUSCLE NERVES IN HUMAN SUBJECTS

Single‐unit impulses were recorded with semi‐microelectrodes from muscular portions of peripheral limb nerves in awake human subjects. Thirteen units were studied. Four of them could not be activated by mechanical peripheral stimuli but they fired steadily during sustained voluntary contractions. They were considered to be either motor fibres or proprioceptor units, having high thresholds to mechanical stimuli. The other nine units were shown to be proprioceptors which had their end organs located in deep structures of the leg or the forearm. They were divided into three groups on the basis of their responses to local mechanical stimuli, passive movements, and voluntary contractions. Possible relations between each group of units and various anatomical types of proprioceptors are discussed. Some of the units had characteristics which suggested that they were muscle spindle afferents. The findings reported in this investigation and in an earlier investigation, dealing with multi‐fibre discharges in muscle nerves, indicate that the muscle spindle afferent discharge is increased during voluntary contractions and thus, that the fusimotor system is engaged in voluntary motor acts. © 1969 Scandinavian Physiological Society