The effects of cutaneous mechanoreceptor stimulation on the stretch reflex.

The effects of cutaneous stimulation on tonic and phasic responses to stretch were studied in the triceps surae complex of unanesthetized, decerebrate cats. The tonic response was produced by a maintained stretch of the muscle group to 80-85% of its maximum length. Stretch was applied directly to the isolated tendon at the calcaneus. Phasic responses were elicited by a ramp stretch of 1.0 to 2.0 mm superimposed on the maintained stretch. Mild, brief, electrical or mechanical stimulation of the plantar cushion caused a sequence of inhibitory and excitatory changes in the tonic EMG activity in the soleus muscle. Mild stimuli, applied 0.01 to 5 ms before the start of ramp stretch, decreased the size of the phasic response to stretch and converted it into a biphasic response. It is suggested that stimulation of cutaneous mechanoreceptors may be responsible for variations in the initial burst of EMG activity seen in the agonist muscle during the response to perturbation or fast voluntary movement in animals and man.