Reciprocal excitation of muscle antagonists by the primary afferent pathway.

Abstract

Measurements were made from electromyograms, evoked in human soleus and tibialis anterior muscles by tendon taps. Evidence is presented to suggest that in certain motor disorders it is possible to stimulate the stretch reflex afferents from a single muscle and elicit activity both in that muscle and its antagonist at comparable latencies and levels. Responses in both muscles occur at the short latencies of an oligosynaptic or even possibly a monosynaptic pathway. We discuss the proposition that the traditional concept of spinal reciprocal innervation as an inhibitory linking of muscle antagonists must be expanded to include both inhibitory and excitatory connections. Such reciprocal excitatory connections appear pronounced in spastic patients who have suffered perinatal injuries to the immature nervous system.