Brainstem Organization of Swallowing and Its Interaction With Respiration

Swallowing acts as a protective reflex for the upper respiratory tract by cleaning the naso- and oropharynx and closing the larynx to prevent pulmonary aspiration. Extensive microelectrode recordings performed in sheep and rat have shown that the swallowing neurons are located in two major brainstem areas. The areas include the dorsal medulla within the nucleus tractus solitarii (NTS) and the adjacent reticular formation, forming the dorsal swallowing group; and the ventrolateral medulla just above the nucleus ambiguus, forming the ventral swallowing group. Complete inhibition of respiration can be produced during high-frequency rhythmic swallowing initiated by superior laryngeal nerve stimulation or activation of excitatory amino acid receptors in the NTS. It can be postulated that, among the different groups of swallowing neurons, local mechanisms in the NTS play a key role. The oropharynx subserves a common pathway for deglutition and respiration, and obviously these two functions must interact to prevent pulmonary aspiration.