The |cilia| are tiny microscopic hairs, which protrude from a thin covering of ~mucous~ within the |nasal cavity|. These hairs help eliminate dust and infectious agents from the ~air~ that is breathed in before they reach the respiratory tract. Constant ciliary action carries these particles to the |nasopharynx|, where they are drawn into the |stomach|. The |cilia| are also important to the sense of smell. Each hair terminates in a small smell receptor cell known as an olfactory receptor. It is believed that these receptors are sensitive to about 30 primary smells. Other smells are made up of mixtures of some or all of these primary smells. When odorous substances activate the |cilia|, the receptors respond by firing off a series of ~nerve~ impulses to the |brain| for analysis.
