Respiration involves the complex coordination of several pump and upper airway/pharyngeal muscles. From a respiratory perspective, the major function of the pharyngeal muscles is to keep the airway patent allowing for airflow in and out of the lung with minimal work by the respiratory pump muscles. The activity of each of the pharyngeal muscles varies depending on its function, but many reduce their activity during sleep. In healthy individuals, these muscles can respond to respiratory stimuli during sleep to prevent airway collapse. However, in individuals with an anatomically small airway, the muscles cannot always compensate for the increased mechanical load. Thus a vulnerable situation in which the airway is prone to collapse may occur with the development of obstructive sleep apnea. This article describes the current understanding regarding the control of the pharyngeal musculature during wakefulness and sleep, as well as the implications for obstructive sleep apnea.