ABSTRACT
The use of the terms ‘‘upper airways’’ and ‘‘lower airways’’ (to indicate regions above and below the larynx) is arbitrary because the airway acts as a single unified conduit. The functions of this airway may be broken down into sections, with the nasal passages acting as both chemosensor and air conditioner, the pharynx acting as a crossroads between the digestive and respiratory systems, the larynx acting as a sensitive protective valve, and the lungs acting as the gas exchange area. The sensory nerve supply to the upper airway has the capacity to detect potentially damaging gases, particulate matter, and the presence of food and fluid. Stimulation of upper airway sensory nerves can initiate reflex responses that either expel the source of the stimulus by sneeze or cough or close off the airway and inhibit breathing.
