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.

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Dive Deeper

Relevant articles, podcasts, videos, and more from around the internet — curated and summarized by our team

Photo of a unpuffed blowfish looking directly into the camera.
Open link on science.org

Creatures like fish rely on suction to consume food, flexing their gills to create water currents that vacuum up their meals. When creatures first crawled from the sea, they likely had to return whenever they wanted help swallowing a snack. The evolution of the tongue enabled vertebrates to completely cut ties with the sea, moving on (and in)land where they could sample new foods and ways to eat them.

Open link on youtube.com

As an octopus pulls itself along the ocean floor, each step tells more about its next meal. Octopus suction cups are filled with modified sensory receptors that can bind with a greater variety of materials and transport a wider array of information, such as flavor, from tactile stimuli. These receptors don't resemble typical sensory system receptors but best resemble receptors that detect neurotransmitters within the body.

Photo of person eating a fingerful of mayonnaise.
Open link on ncbi.nlm.nih.gov

If you've ever seen a tongue map where the organ is broken into sections exclusively responsible for tasting certain flavors, you've been led astray. The original tongue map created by German researcher D.P. Hanig recorded reported taste sensitivities of human subjects in psychological studies. His findings were later translated and taken out of context, possibly giving rise to the faulty tongue map.

Photo of a glass of bubble tea.
Open link on knowablemagazine.org

Once your bubble tea has sloshed its way to the digestion system, taste or nutrient receptors there tell the body what it's dealing with so that the proper digesting enzymes can get to work. These digestive system taste receptors help control the flow of nutrients from the gut, meaning further research into its sweet receptors could open a new path to treating Type 2 diabetes.

Open link on nature.com

Cats—obligate or hypercarnivores that must eat meat to stay alive—are "behaviorally insensitive" to sweets due to taste receptor mutations. If sweetness doesn't influence one's survival chances, then mutations can gather, eventually blocking perception of it altogether. This holds true for other "-vore" categories. Pandas, for example, are unable to taste umami because they only eat bamboo, making protein and its flavors irrelevant.

Open link on youtube.com

Commercially caught fish are often killed through suffocation, allowing the fish to flop its way to a slow death. This causes the fish extreme stress (obvious, we know), flooding their bodies with stress hormones and lactic acid. These chemicals cause the fish's flesh to become bitter where it was once rich and quickens the rotting process. A better way? Stabbing it in the brain.

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