STRUCTURE AND FUNCTION OF THE UPPER AIRWAYS

Nose

The normal airway begins functionally at the nares. As air passes through the nose, the important functions of warming and humidification occur. The nose is the primary pathway for normal breathing unless obstruction by polyps or upper respiratory infection is present. During quiet breathing, the resistance to airflow through the nasal passages accounts for almost two thirds of the total airway resistance. The resistance through the nose is almost twice that associated with mouth breathing. This explains why mouth breathing is used when high flow rates are necessary as with exercise.

The sensory innervation of the nasal mucosa arises from two divisions of the trigeminal nerve. The anterior ethmoidal nerve supplies the anterior septum and lateral wall, whereas the posterior areas are innervated by nasopalatine nerves from the sphenopalatine ganglion. Local anesthesia can be produced by blocking anterior ethmoidal and maxillary nerves bilaterally; however, simple topical anesthesia is usually quite effective.