The olfactory system (smell system) allows the body to detect chemicals in the environment. Along with the gustatory system, the olfactory system also allows the body to distinguish flavors. Most of the olfactory system, however, is devoted to alerting the body to dangers in the environment. Humans can smell several hundred thousand substances, but only about 20% of them are interpreted as pleasant.

In the dorsal part of the nasal cavity is a thin bony structure called the cribiform plate. On the ventral surface of the plate is the olfactory epithelium, which contains three types of cells. Olfactory receptor cells, the dendrites of olfactory neurons, transduce chemical messages into nerve impulses. Supporting cells, which are somewhat like the glia of the central nervous system, produce mucus. Basal cells produce new olfactory receptor cells, which wear out and...