HAND MUSCLE REFLEXES FOLLOWING AIR-PUFF STIMULATION

Hand muscle reflexes following muscle stretch and electrical nerve sti mulation show a typical pattern consisting of short- and long-latency reflexes. The present investigation was designed to test reflexes foll owing pure cutaneous stimulation. Air puffs were delivered to the palm ar tip and the nail bed of the first, second and fifth fingers during isotonic contraction of hand muscles. The EMGs from the thenar muscles , the first dorsal interosseous muscle and the hypothenar muscles were recorded. Reflexes were obtained in all muscles, with a typical confi guration consisting of a short-latency excitatory component (cutaneous long-latency reflex I, cLLR I) and a second excitatory component (cut aneous long-latency reflex II, cLLR II), with an inhibitory component between them. The size of cLLR II differed depending on the area stimu lated and the muscle recorded. We found the largest responses always i n the muscle acting on the stimulated finger. The reflex size depended on the strength of air puff stimulation. Allowing small displacements of the fingers led to an additional increase in the size of the refle x. The pattern of reflexes was identical independent of whether the fi nger tip or the nail bed was stimulated, but the size of the reflexes was smaller following nail bed stimulation. Following blockade of the cutaneous nerve branches of the thumb with local anaesthetics, air puf f stimulation of the thumb no longer elicited this reflex pattern. Hen ce, under our experimental conditions, cutaneous receptors were the on ly source of afferent input for these reflexes. The results suggest th at these cutaneous reflexes are mainly dedicated to controlling the st imulated finger independent of whether the palmar tip or the nail bed is stimulated. A possible physiological function is the adapting of gr ip force during handling of delicate objects if a perturbation is appl ied either to the object or the hand.