VELOCITY SENSITIVITY OF HUMAN MUSCLE-SPINDLE AFFERENTS AND SLOWLY ADAPTING TYPE-II CUTANEOUS MECHANORECEPTORS

1. Velocity information is used in the performance of movement. This s tudy evaluated the ability of peripheral receptors to signal velocity in human subjects. 2. The velocity sensitivity of human muscle spindle afferents from the extensor digitorum muscles and slowly adapting typ e II cutaneous mechanoreceptors on the dorsum of the hand was evaluate d with recordings from tile radial nerve during imposed flexion moveme nts about the metacarpophalangeal joint. Twenty-degree movements at ve locities ranging from 5 to 80 deg s(-1) were used. 3. Three measures o f dynamic response were calculated: the dynamic positional sensitivity (the relation between discharge rate and joint angle during the dynam ic phase of movement), the dynamic index (the discharge rate just befo re ramp completion minus the rate 0.5 s later), and the incremental re sponse (the discharge rate just before ramp completion minus the rate just before ramp onset). 4. Both muscle spindle afferents and slowly a dapting type II cutaneous mechanoreceptors demonstrated significant ve locity sensitivity. The magnitudes of tile relations between dynamic r esponse measures and velocity were similar in the two receptor types. 5. These findings are consistent with the view that both muscle spindl e afferents and slowly adapting type II cutaneous mechanoreceptors pro vide reasonable velocity signals.