Taste Buds

Background

Taste buds do more than let you experience your favorite food. These peripheral organs can sense the chemical makeup, potential toxicity, and fleeting experience of flavor, giving the body a chance to respond to undesirable chemicals or tell the brain that you should reach for another scoop. 

Anatomy

A mammal's tongue is covered in four types of small bumps known as papillae, three of which detect taste and at least one of which detects texture, temperature, and pain. These papillae—circumvallate, fungiform, and foliate—each have several taste buds, which are garlic-shaped structures made up of 50 to 100 chemosensory taste cells.

Each taste cell contains receptors for certain tastes, of which there are officially five: sweet, sour, salty, bitter, and umami (though more may exist). 

Location

If you've ever seen a tongue map, where sections of the tongue were reserved for different tastes, then you've been led astray. 

Taste receptors venture far beyond the tongue, a fact made more digestible when one thinks of them as sentinels that react to foreign substances as they enter the body. They communicate chemical information rather than flavor.

Receptors across the tongue, nose, and other areas can also trigger bacteria-fighting responses (see study here). Bitter taste receptors in the nose and mouth can cause their host cells to wiggle tiny, hairlike projections that can flick away bacteria. They also trigger cell's defensive behavior, sending out antimicrobial proteins and nitric oxide to put an end to any intrusion.

These chemosensory receptors have been found across the body, including the lungs, gut, and testicles (learn more here). 

Neuroscience

Flavor and taste are different. Taste is the sensory perception captured by taste cells, while flavor refers to the overall eating or drinking experience, which includes other sensations, such as smell and texture.

The taste receptors that help create flavor send information about food and drink to the brain's gustatory cortex via at least five neurotransmitters secreted in response to chemical exposure.

The gustatory cortex refers to the part of the brain, so far understood to be the insula and operculum in the cerebral cortex, which assigns meaning to the chemical input relayed by taste receptors. Each taste receptor responds to particular chemical compounds in food and drink (see scientific deep dive). 

Evolution

The tongue's taste receptors provide "an evolutionarily old hedonic compass for what and what not to ingest." Sweet foods tend to provide energy- or calorie-rich nutrients, and bitter foods that can trigger revulsion warn against potentially noxious alkaloids, often found in plants that are toxic when ingested.

The story of taste's evolution is really about the loss of it, according to one university biologist. If a certain flavor doesn't influence one's survival chances, then mutations can gather and eventually block the perception of it altogether, such as in the case of cats and sea lions, both of which can't taste sweetness.