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Welcome back to NeuroTransmissions. I’m Alie Astrocyte.
Taste is very subjective, isn’t it?
Some people don’t like sweet things, while others, like me, can’t get enough.
How does taste even work? Let’s find out!
Brain freeze!
Taste is also called gustation.
Just like smell, taste is a chemosensation.
It breaks down and interprets chemical signals from the food and drink you put in your mouth.
You probably already know that you can taste things thanks to the taste buds on your tongue.
All of those tiny little bumps you can see when you stick your tongue out are
covered in hundreds of taste buds and each taste bud contains between
50 and 100 individual taste receptor cells.
There are two major families of taste receptor.
Type 1 is the “sweet” family, while Type 2 is the “bitter” family
and different combinations of receptors within those categories
determine the different tastes we experience.
Currently, science recognizes five major categories of flavor:
sweet, salty, bitter, sour, and “umami”,
which is a Japanese word meaning “pleasant savory taste”.
Let’s talk about each of the different flavors, and what science knows about how we taste them.
It’s hard to find someone who doesn't like sweet things.
Sweetness is what we taste when a food is full of simple carbohydrates,
like sugar, and our taste buds can be tricked with artificial sweetener too.
Sweetness is detected with a G-coupled protein receptor on your taste receptor cells from
the Taste Receptor 1 protein family, which means that when a sweet molecule binds to
the receptor, it triggers a change in the protein that sets off a chain reaction that
has an effect somewhere else in the cell.
In sweet-detecting cells, two proteins together, called T1R2 and T1R3, combine to form the receptor
In this case, it allows calcium into the cell, encouraging the depolarization
of the cell, so it can send a signal to the brain.
We mostly taste salty things because they contain sodium ions.
We haven’t uncovered a definite “salty” taste receptor, but we think that the sodium
ions directly enter the receptor cell via sodium channels, causing the cell to depolarize
and send its signal on down the line.
Scientists think that evolving the ability to taste bitterness was very important for our survival.
Many toxic compounds have a generally bitter taste, so being able to detect
the bitterness would have kept us from chowing down on poisonous plants.
Still, many people develop a taste for bitterness.
It’s a primary component of the flavor of coffee, dark chocolate, and broccoli.
Like sweetness, bitterness depends on G-coupled protein receptors.
This time from the Taste Receptor 2 family.
We have several different kinds of bitter receptors, and over 550 different
bitter-tasting compounds have been identified by scientists.
How sour something tastes has to do with how acidic it is.
Sourness, like saltiness, is tasted primarily because of
the direct entry of ions into the taste receptor cell.
In this case, it’s because acids release hydrogen ions - essentially, just protons.
We’re not totally sure yet how this works, but we think that these positively charged
protons travel through ion channels to trigger an electrical change within the cell,
and this depolarizes the cell to trigger the start of the signal.
Umami receptors detect a molecule called glutamate, found in
savory flavors like mushrooms and meat broths.
Like sweetness and bitterness, the umami receptors are g-coupled protein receptors.
In this case, T1R1 and T1R3.
Now, imagine you’ve just taken a bite of this delicious ice cream.
And now your sweet receptors are all signaling your taste receptor cells to fire.
How does that signal reach your brain and let you know that you’re enjoying the taste of ice cream?
There are three major cranial nerve pathways that participate in this transmission.
The facial nerve, glossopharyngeal nerve, and vagus nerves receive signals from the
front, middle and back parts of your tongue, respectively, and pass that information on
to a brain structure called the solitary tract nucleus, or NTS for short.
From there, the information is passed up to the gustatory neocortex,
where higher-order processing can occur.
The different taste sensations are preserved all the way up to this level,
and different cells in the cortex respond to each of the five taste types,
as well as coding the intensity of the taste.
Studies in primates have indicated that these cells signal less when an animal is full and
that some neurons fire in response to images or the smell of food.
This means that the gustatory neocortex is probably important for identifying and choosing foods.
One thing we don’t know very much about is how we attach pleasure to different tastes.
Because taste is so subjective, and because you can “train” yourself
to learn to like new foods, there’s probably some very interesting neuroscience behind
the connection of taste to value.
We just don’t know that much about it, but maybe ten years from now,
science will have it all figured out!
Have some questions or other info you want to share? Put them in the comments below!
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Join us next week to learn a little bit about the last major sense:
Touch.
Until our next transmission, I’m Alie Astrocyte. Over and out!