NEURONAL MECHANISMS IN SWALLOWING.

Abstract

1. Neuronal mechanisms of swallowing were investigated by means of single fiber recordings from afferent (superior laryngeal) and efferent (hypoglossal and vagus) nerves and by means of extracellular micro-electrode recordings from nerve cells in the solitarius, ambiguus and hypoglossus nuclei in unanesthetized, midcollicularly decerebrate cats. 2. Afferent fibers showed a great variety of patterns of discharge during swallowing and the same was true for nerve cells in nucleus solitarius. Efferent fibers, on the other hand, and nerve cells in ambiguus and hypoglossal nuclei showed much less variability, their response consisting primarily of a short burst of action potentials synchronous with activity in geniohyoid muscle. 3. Gallamine-induced motor paralysis abolished all swallowing response of afferent nerve fibers and of nerve cells in nucleus solitarius but left unchanged that of efferent fibers and of nerve cells of ambiguus and hypoglossus nuclei. Motor paralysis did not alter the response of nerve fibers or cells to electrical and mechanical stimulation of mucosa and deeper structures in the oropharyngeal cavity. 4. Nerve cells in ambiguus and hypoglossus nuclei could be divided into two groups. One consisted of nerve cells which were “silent” when first encountered but became momentarily active during swallowing. The second group comprised nerve cells discharging rhythmically in phase with respiration, also producing a short burst of action potentials during swallowing. Response of the latter group to swallowing disappeared when the animal was asphyxiated but that of nerve cells in the first group and efferent fibers of hypoglossal and vagus nerves persisted. 5. The functional organization of nerve cells controlling swallowing and its relationship with central respiratory mechanisms is discussed.