Motor-unit reflex inhibition in different regions of the human masseter muscle

Regional localization of reflexes is common in anatomically complex limb muscles, but it is uncertain whether this occurs in the multipinnate human jaw-elevator muscles. In this study, motor-unit (MU) inhibitory reflex behaviour was examined in different regions of the human masseter using a strictly controlled method in which stimulus conditions, MU firing frequency, and motor task were matched. All MUs were inhibited by a non-noxious electrical stimulus delivered to the oral mucosa. Although there were significant differences between MUs in the duration of inhibition, this was not dependent on the location of the MUs within the muscle. It was concluded that MU inhibitory reflex behaviour in the masseter is not region specific.