Auto-regulatory neuromechanism of the tongue muscle activity.

Tongue muscles are non-joint moving muscles and consist of extrinsic and intrinsic muscle groups. Contraction of the extrinsic tongue muscle group can produce fast movements of the tongue for protrusion, retraction or lateral deviation, and contraction of the intrinsic muscle group may produce a delicate change in shape of the tongue. The tongue is constantly in action during mastication, deglutition and speech, and the basic physiologic mechanisms of such well organized fine movements of the tongue might be attributed to some reflex system. However, there are still many discussions on the detailed physiologic mechanisms of such a system. Especially, the proprioceptive innervation of the tongue except in humans is still not clear, in spite of many morphological studies3,4,5,6,10,21,25,29). In the present experiment, cats were used and three different procedures were carried out to clarify the neural feedback system controlling tongue muscle activities. The first was an analysis of individual tongue muscle activity, the second a recording of afferent nerve impulses from the tongue, and the third a recording of the response in the medulla induced by stretch of the tongue.