By David Dunning – Updated Aug 30, 2022
When molecules from food or the environment enter the nasal passages and mouth, they dissolve in the watery mucus lining these areas. They then bind to specific receptor proteins embedded in the cell membranes of sensory neurons. This binding event triggers an electrical signal that travels along a dedicated neural pathway to the brain, where distinct regions interpret the chemical cues and associate them with memories, emotions, and behavioral responses.
In humans, the olfactory epithelium—just a tiny region less than 1/3 square inch in each nostril—houses roughly 50 million receptor cells. Each cell carries up to 20,000 hair‑like projections called cilia that extend into the mucus layer, providing a vast surface for odorant molecules to interact. The human olfactory system can discriminate thousands of distinct scents, provided the odorants are at least partially soluble in water or fat. For more on olfactory receptors, see the NIH review on olfactory receptor diversity.
Taste perception originates from taste buds located on the tongue’s papillae. Each bud contains 50–150 receptor cells and responds to five primary taste qualities: salt, sweet, sour, bitter, and umami—the savory, meat‑like flavor associated with glutamate. The papillae—circumvallate, foliate, and fungiform—cover the dorsal, lateral, and anterior surfaces of the tongue, ensuring a broad detection of chemical stimuli. For detailed anatomy, refer to the gustatory system overview.
Although the neural pathways for olfaction and gustation are anatomically distinct, they frequently converge to create a unified flavor experience. Much of what we perceive as “taste” actually arises from olfactory signals that travel to the brain during eating—especially when food is heated or chewed, releasing volatile compounds that reach the nose. This synergy helps regulate appetite, trigger pleasure or aversion, and anchor vivid memories of meals.
While we have identified five distinct taste receptors, research suggests there may be hundreds of olfactory receptors, underscoring the complexity of chemical detection in humans.
