The effect of afferent stimuli on steadily discharging single motor units in man.

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Abstract
The effect of afferent stimuli on the firing pattern of single motor units was studied in the human 1st dorsal interosseous muscle of the hand. A reproducible series of changes in the probability of motor unit firing was seen. There was evidence for an excitatory spinal reflex involving median nerve muscle afferent fibers and ulnar nerve motor fibers. Cutaneous and muscle afferent pathways expected to be important in the control of fine movement of the 1st digit produced an excitatory reflex response at about 70 ms. All sites stimulated in the ipsilateral limb gave rise to a profound reduction in motor unit firing from about 70 to 130 ms.