The average human mouth and throat are home to about 10,000 taste buds, and each one contains around 100 receptors. There are several kinds of taste receptors, and although most of them are in the mouth, they are also scattered around in different body parts.
In “Taste and Its Complications” we mentioned the evolutionary value of this alarm system that warns the organism of encroaching toxins. When receptors are triggered by certain kinds of chemical molecules, they in turn tell the body to mobilize a defense mechanism. Then the body will sneeze, vomit, or take other action to basically get that stuff out of there.
Are there 14 basic tastes really?
An unlikely choice for the title of Basic Taste is carbon dioxide, the fizz in fizzy drinks, a sensation which has always been assumed to inhabit the realm of touch, but which might actually be a flavor. Another contender is kokumi, which means heartiness or “mouthfulness.” It is said to originate in foods that are aged, braised, or slow-cooked. However, kokumi was defined and glamorized by Ajinomoto, the company that gave the world umami (MSG), so its claim is seen as problematic. Another source adds “astringent” as a possible basic taste.
And then, there is plain old water, which only a couple of years ago began to be considered by neuroscientists as a candidate for one of the tastes — with a caveat. In fact, science seems rather confused. In 2017, Ephrat Livni wrote in her article for Quartz,
A study published in Nature […] shows that mammals respond to the stuff at a cellular level, on the tongue… Water may not be a taste all its own, however… On the one hand, this work seems to indicate that water is its own “taste” to the extent that specific taste receptor cells respond… But technically speaking, those TRCs have already been connected to our ability to taste sour.
The receptor cells in the mouth send a message to the brain, letting it know that water is being drunk. Mice are wired this way, and presumably humans also. But now, it gets interesting. The water receptor cells are not unique. They are the same ones that recognize the long-acknowledged basic taste known as sour.
How is it that the same receptors alert to both water and sour, and yet can tell the difference between them? Because what they probably are tasting is pH, the metric that describes acidity versus alkalinity. In addition, the activation of receptors to message the brain is not the only thing going on.
The story of how California Institute of Technology researchers figured this out is pretty amazing:
[T]he team used a technique called optogenetics that allowed them to stimulate sour cells with light instead of water. The researchers removed water from the animals’ water bottle and made it so that the bottle’s spout emitted a blue light when the animals touched it. They discovered that thirsty genetically engineered mice would go to the spout for water, encounter the light and “drink” it.
Even though a mouse brain can be tricked into thinking it is drinking water, it also knows somehow that the body is not really being hydrated. This is evident because the mouse does not stop the fake drinking. It really is all very strange.
Your responses and feedback are welcome!
Source: “It turns out that we may have more than five basic tastes,” QZ.com, 06/01/17
Source: “Turns out, that humans may actually be able to taste water,” IndiaTimes.com, 06/04/17
Photo credit: Kiki Sorensen on Visualhunt/CC BY
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