DISCHARGE PATTERNS OF LINGUAL SPINDLE AFFERENT FIBERS IN HYPOGLOSSAL NERVE OF RHESUS MONKEY

Muscle spindles have been identified in both the intrinsic and extrinsic musculature of the rhesus monkey tongue. The purpose of this study was to determine whether spindle afferent fibers were present in the hypoglossal nerve of the monkey and to ascertain the responses of these fibers to stretch of the tongue. Single units were isolated from the distal region of the main trunk and from both end branches of the hypoglossal nerve in seven animals and the responses of these units to various directions of stretch determined. The results indicated that spindle afferent fibers run within the distal region of the hypoglossal nerve main trunk in the monkey. Ten discrete discharge patterns were discerned in the 75 hypoglossal units from which recordings were taken and their potential significance discussed in relation to the type of information the lingual spindles may be forwarding to the central nervous system. © 1968.