Introduction

In organisms as complex as vertebrates, structures serving a particular physiological system often play roles in other major systems as well. Obvious examples are the shared equipment of the digestive and respiratory tracts at the head end of the organism and of the genital and urinary tracts at the other end. Shared structures of this sort require a sort of biological time-sharing with regard to function. One can breathe or swallow, but not at the same time without embarrassing consequences.

A more subtle co-ordination of functions must exist within the system that we use for both respiration and phonation. Breathing and vocalization are not mutually exclusive, but are interdependent. The co-ordination of movements for these two purposes and the integration of reflexes that serve them constitute an important problem in regulatory physiology. Since the larynx is not only a respiratory valve, but also the organ of speech and song, we hope the discussion will be of interest to students of both systems.

Because vocal and respiratory science have evolved nearly independently, it is not surprising that certain responses that actually influence both systems are historically entrenched as the property of one or the other. A good example is the coordinated set of reflex responses mediated by pulmonary stretch receptors. These are the well-known Hering-Breuer reflexes, which have been firmly associated with the regulation of respiratory tidal volume for more than a century (Breuer, 1970). Despite this association, these reflexes appear to be at least as effective in maintaining upper airway patency as in regulating lung volume (Sica, et al., 1984; Kuna, 1986; Bartlett and St. John, 1988), and as noted later in the chapter, they may well play a role in the co-ordination of vocalization as well.

Our purpose is to examine some factors that influence both breathing and phonation. We begin by presenting a brief review of the respiratory physiology of the larynx. We then report some recent ideas and findings about the influence of respiratory reflexes during evoked vocalizations in animals and the apparent gating of protective reflexes during phonation. The closing section consists of comments and discussion about the importance of reflex control of motor activity during speech and other complex movements.

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