Human masseter muscle: H- and tendon reflexes. Their paradoxical potentiation by muscle vibration.

We developed a method for direct electrical stimulation of the masseter nerve in man. Both direct M-reponses and genuine H-reflexes were recorded from the ipsilateral masseter muscle. Muscle vibration that inhibits the Achilles tendon reflex and the soleus H-reflex was found to potentiate the masseter tendon reflex and also the masseter H-reflex. This unexpected contrast may be related to peculiar brain stem circuitry of the masseter reflex mechanism.