Swallowing and Other Related Reflexes

Abstract

Mastication and swallowing can be viewed as a part of alimentary behavior (see Dellow, 1976). Swallowing can be assigned airway functions as well (see Storey, 1976a). It is instructive to consider both these complex reflexes within the framework of reflexes serving the upper airway and alimentary tract (see Fig. 59). Reflexes initiated from a number of sites in these two tracts can be functionally designated as supportive and protective reflexes. While the former are related to air and food intake, the latter are concerned with the prevention of entry into or expulsion from the airway or alimentary tract of inappropriate substances. Suckling, mastication, and swallowing are easily assigned to supportive reflexes of the alimentary tract, while spitting, gagging, and vomiting can be assigned to protective reflexes of the same region. What is not generally recognized is that swallowing is also a protective reflex of the upper airway along with apnea, sneezing, sniffling, glottic closure, and coughing. Kahn (1903) was the first to suggest that swallowing protected the airway; the finding that water stimulation of the larynx is a most effective means of initiating swallowing from the larynx of several species of animals (see below) prompted its assignment to this role (Storey, 1968a). Swallowing initiated from the larynx may guard the larynx from invasion from the alimentary tract of saliva or liquid bolus residues and esophageal regurgitation or from the respiratory tract of nasopharyngeal and tracheal secretions, especially during periods of upper airway infection. For further discussion of the hierarchical organization of these airway reflexes and the manner in which the most appropriate reflex is elicited, see Storey (1976a).