Facilitatory effect of lingual nerve stimulation on masseteric EMG Activities of the cat

Unitary EMG activities in masseter muscle of decerebrate cats were recorded during repetitive stimulation (20-50 Hz) of the lingual nerve and during vibration. These two kinds of stimuli facilitated EMG activities, whereby their effects could summate. Masseteric EMG response was also obtained during jaw opening phase of the cyclic jaw movement. With the jaw cyclically moved at a widely opened position: motor units discharged even at the jaw closing phase during simultaneous lingual nerve stimulation or during vibration. Based on the results obtained, two possible pathways for lingually induced excitation of masseteric EMG can be speculated on: an excitatory pathway from the lingual nerve to the masseteric motoneurons, secondly a direct pathway to masseteric motoneurons. As facilitation of masseteric EMG was obtained with the threshold lower than that of jaw opening reflex, separate afferent fibers concerning these two reflexes should also be considered.