Miosis is a decrease in pupil size as a result of paralysis of the iris dilator muscles
. The sphincter and dilator muscles
of the pupil are innervated, respectively, by the sympathetic and parasympathetic systems.
Multiple factors can influence output from the hypoglossal motor nucleus to the major upper airway dilator muscle (the genioglossus) (70-76).
For example, a hypnotic agent provided to OSA patients with a low arousal threshold but recruitable upper airway muscles may allow enough time for C[O.sub.2] and negative pressure to accumulate sufficiently to augment dilator muscle activity yielding improvements in pharyngeal patency.
Following arousal from sleep, augmented pharyngeal dilator muscle activity and a robust ventilatory response to arousal generally occur (Fig.
Normally, the diameter of the upper airway increases during inhalation and decreases during exhalation, The changes in upper airway diameter during respiration is thought to primarily result from increased activation (during inhalation) and decreased activation (during exhalation) of pharyngeal dilator muscles
such as the geniohyoid, sternohyoid, genioglossus, and stylopharyngeus muscles.
Reflex arcs involving these upper airway dilator muscles
are integrated with the central mechanisms that control ventilation and breathing.
Fregosi, "Influence of posture and breathing route on neural drive to upper airway dilator muscles
during exercise," Journal of Applied Physiology, vol.
In addition to the typical muscular coat of the foregut, the pharynx has dilator muscles that aid in conveying food from the buccal cavity to the esophagus (Chapman 1985; Skaer 1993).
The epithelium is invested by the visceral and dilator muscles. It is lined with a 2.5 [mu]m thick dorsal cuticular intima, the middle portion of which is curved upwards with right and left halves connected by an elevated bridge.
Upper airway collapsibility may reflect the impaired function of upper airway dilator muscles
such as the genioglossus muscle.
This activation increases the tone of the upper airway dilator muscles
. Increased muscle tone allows the airway to remain open as a person quickly takes deep breaths in order to lower the CO2 level.