Olfactory Receptors

Smell and taste are both carried by chemoreceptors — receptors that respond to dissolved or airborne chemical molecules rather than to physical stimuli like light, sound or pressure. The receptors for smell specifically are excited by airborne chemicals that dissolve into the fluid lining the nose, and sit in patches of yellow-tinged tissue called the olfactory epithelium, located on the roof of the nasal cavity. This epithelium is covered by a thin mucus layer on its exposed surface and bordered above by connective tissue containing olfactory glands.

The olfactory epithelium contains three cell types: supporting cells, basal cells, and millions of pin-shaped olfactory receptor cells — themselves an unusual example of bipolar neurons, since most bipolar neurons elsewhere are confined to sensory structures like the retina. The supporting cells and the associated olfactory glands together secrete the protective mucus layer. The unmyelinated axons of the olfactory receptor cells bundle together to form the filaments of the olfactory nerve (cranial nerve I), which pass through tiny openings (foramina) in the bone above and synapse with cells of the olfactory bulb, just under the frontal lobe. From there, the impulse travels via the olfactory tract to the frontal lobe of the cerebrum, where the smell is actually identified, and separately to the limbic system, which generates …