nose, the prominent structure between theeyes that serves as the entrance to therespiratory tract and contains theolfactory organ. It provides air forrespiration, serves the sense ofsmell, conditions the air by filtering, warming, and moistening it, and cleans itself of foreigndebris extracted from inhalations.

The nose has two cavities, separated from one another by a wall ofcartilage called the septum. The external openings are known as nares ornostrils. The roof of themouth and the floor of the nose are formed by the palatinebone, the mouth part of which is commonly called the hardpalate; a flap oftissue, thesoft palate, extends back into thenasopharynx, the nasal portion of thethroat, and during swallowing is pressed upward, thus closing off the nasopharynx so that food is not lodged in the back of the nose.

The shape of thenasal cavity is complex. The forward section, within and above each nostril, is called thevestibule. Behind thevestibule and along each outer wall are three elevations, running generally from front to rear. Each elevation, called anasal concha or turbinate, hangs over an air passage. Beside and above the uppermost concha is the olfactory region of the nasal cavity. The rest of the cavity is the respiratory portion. The respiratory area is lined with a moistmucous membrane with fine hairlike projections known as cilia, which serve to collect debris.Mucus from cells in the membrane wall also helps to trap particles of dust, carbon, soot, andbacteria.Sinus cavities are located in the bonyskull on both sides of the nose.

Britannica Quiz

Facts You Should Know: The Human Body Quiz

In theolfactory (smelling) portion of the nose, most of the lining is mucous membrane. A small segment of the lining contains thenerve cells that are the actual sensory organs. Fibres, calleddendrites, which project from the nerve cells into the nasal cavity, are covered only by a thin layer of moisture. The moisture dissolves microscopic particles that the air has carried into the nose from odour-emitting substances, and the particles dissolved in thefluid stimulate the olfactory nerve cells chemically.