The nose is the only organ of the respiratory system that resides outside of the body. As we breathe, air enters the body through the nostrils or external nares. The area inside the nose is known as the nasal cavity. The nasal septum divides the nasal cavity medially. The olfactory receptors are located in the mucosa in a small area on the roof of the nasal cavity (see the special senses). The respiratory mucosa lines the nasal cavity. This mucosa helps warm air entering the body. It also helps moisten the air and trap invading pathogens.
The walls of the nasal cavity are uneven. There are three mucous covered projections that
stick out into the nasal cavity. These lobes are known as conch. These projections help
increase the area that the mucosa can affect. The nasal cavity is separated from the oral
cavity by a palate of bone. Anteriorly, where the palate is supported lies the hard plate.
The unsupported area of the palate houses the soft plate.
The paranasal sinuses surround the nasal cavity. These sinuses are located in the
maxillary, ethmoid, sphenoid, and frontal bones. The sinus chambers help lighten the
weight of the skull. The sinus chambers also act as resonance chambers for vocalization.
The sinus cavities also secrete mucous for the nasal cavity.
The pharynx is the muscular passageway that provides a means of transportation for air and
food. The pharynx, also known as the throat, is about 13 cm. long.
