In this video I explain the process of transduction for taste and how gustatory cells detect tastant molecules in food. I discuss structures of the tongue, including papillae, taste buds, and gustatory cells and consider evolutionary explanations for changes in the number of taste buds over time. I also mention the phenomenon of supertasters, who are more sensitive to taste and can detect compounds that non-supertasters cannot. Finally I consider how the experience of taste arises from the stimulation of 5 main types of gustatory cells, as well as the stimulation of other receptors, other senses, and even beliefs and expectations.

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Recommended Videos:

Linda Bartoshuck on Supertasters:
http://klru.pbslearningmedia.org/resource/nvsn6.sci.bio.taster/what-is-a-supertaster/

NOVA Science Now – The Science of Picky Eaters:
https://www.youtube.com/watch?v=mffC4hKBd2A

Taste Perception and Colored Jello
https://www.youtube.com/watch?v=1oX7hJLDtpU

Penn and Teller Water Taste Test
https://www.youtube.com/watch?v=YFKT4jvN4OE

Video Transcript:

Hi, I’m Michael Corayer ad this is Psych Exam Review. In this video we’re going to look at gustation, or our sense of taste. So we’re going to be focusing on the mouth and in particular the tongue.

So if you look closely at your tongue, you’ll see it’s covered in bumps. These bumps are called papillae. For the most part, papillae are involved in taste perception. This is because they’re covered in tiny structures called taste buds. So in your mouth you have about 5,000 to 10,000 taste buds. These are inside your papillae. You might think this is a large difference between 5,000 and 10,000. So what’s that about? Well, when you’re a child you have many more taste buds. But as you age, you lose them. By age 20 you’re down to about 5,000 taste buds.

So what’s the reason for this and how does this explain some things that we might notice? One thing we might notice is that children are picky eaters. They’re much more sensitive about what they’ll eat and what they won’t than adults. Part of the reason for this is that they’re more sensitive to certain tastes because they have more taste buds.

One taste in particular that they’re more sensitive to is bitter taste and there’s an evolutionary reason for this. Things that are poisonous tend to taste bitter so we want to avoid them. We want to be especially careful with bitter things. Whereas sweet things are generally safe and so children have no problem eating things that are sweet.

Now you also can understand why adults enjoy certain bitter foods that children can’t stand to eat. Things like broccoli and brussel sprouts which are bitter, children don’t like them. They certainly don’t like things like beer and coffee. These flavors are much too bitter for children. Part of the reason for this is that they have many more taste buds.

If we continue out evolutionary view we can realize that by the time you’re 20, you’ve figured out what you can eat and what you can’t. You know what foods are safe so you no longer need to rely on your taste buds to tell you what you should eat. If you’ve made it that far, if you’ve made it to age 20, you pretty know what is food and what isn’t.

Whereas when you’re a young child you don’t necessarily know and you need to learn that. Now there are also people who are especially sensitive to certain tastes and these are people called super-tasters. So part of the reason super-tasters are so sensitive is that they have more papillae on their tongue. Their papillae are more closely packed together, this makes their sense of taste more sensitive.

They also can detect compounds that other people can’t detect. So if you’re a super-taster you can actually detect this compound called 6-n-proplythiouracil. This is a very very bitter compound. Most people can’t even detect it and it’s in vegetables like broccoli, cabbage, and brussel sprouts. So this explains why super-tasters will find these foods excessively bitter, right? Unpleasant to try to eat. Whereas people who can’t detect this particular chemical compound have no problem eating these foods.

OK so let’s take a look at what a taste bud actually looks like. Let’s imagine we’re looking at the surface of the tongue here and then we’re going to have a sort of gap here.

So this would be a taste bud and there would be many of these on a single papilla. There’s a little opening called a taste pore. Inside that we can see these little tiny hairs called microvilli. And these microvilli are projecting off of specialized taste receptors. Inside the taste bud here we have all these cells in here this sort of looks like an onion. This taste bud would have 50 to 150 of these cells inside. These are called gustatory cells.

This is very similar to the olfactory receptor neurons that we learned about. Remember they could interact with molecules and certain molecules will stimulate certain olfactory receptor neurons. The same is true for gustatory cells, so what happens is the tongue is covered in saliva here, and then we get tastant molecules in the food, these are molecules that we can detect, and they dissolve in the saliva and so they get into the taste pore where they interact with the microvilli.

Different tastant molecules will stimulate different gustatory cells and therefore have different flavors. And then of course different foods will have different combinations of tastant molecules and that will lead to different patterns of stimulation of these gustatory cells and that would lead to the different tastes that we experience.

And then all the messages from these gustatory cells here are going to be sent out they have projections leading out of the taste bud and then they go to the brain where they go to the gustatory cortex. The gustatory cortex is located partly in the frontal lobe and then also in the area to cortex called the insula.

You might remember from a video I previously mentioned that the insula is like this hidden section of cortex. It’s in between the lateral fissure where you have the temporal lobe and then you have this crevice before you get to the frontal lobe and there’s some cortex inside there. That’s the insula and part of the role of the insula is this gustatory cortex that’s responsible for taste perception.

Ok, so next you might ask, “what kinds of tastes can we detect? What kinds of gustatory cells do we have?”. So there’s five main tastes that we can detect.

An important point here is that within each taste bud, you’re going to have all of these different gustatory cells. When you were a kid you might have done some drawing activity in elementary school science where you colored in the tongue with a salty area, a sweet area, something like that. That’s totally a myth. Total garbage, it’s not true at all.

There are not specialized regions of the tongue for different flavors. Based on a mistranslation and misinterpretation of a study on sensitivity and it’s totally wrong but for some reason it still continues it still persists, in elementary schools children are still doing this. I don’t know why. But rid that myth from your mind.

Remember that any of your taste buds are going to have receptors for all of these different tastes. So what are these tastes that we have? First thing, things like sodium are going to interact with some of the cells and that’s going to be responsible for salty flavors then we have sugars and they’re going to respond to certain gustatory cells. So that’s going to give us sweet flavors. Then certain types of acids like citric acid are going to bind to certain receptors here and those are going to give us sour flavors.

Then we have bitter flavors that I mentioned before. Then lastly we have one that you might not be familiar with and this is umami. So umami is a savory flavor. So what does that mean? This is a new one that was added by Japanese researchers and they found that we have receptors for this umami flavor. Savory flavor is like the richness of meat and cheese. A good example of this would be monosodium glutamate, MSG, which is added to food and it makes the foods taste richer. It makes them more savory. If you add it to water it makes it taste more like a rich broth rather than just water, it makes it actually taste thicker even though it isn’t. So that’s the umami flavor.

You might be wondering when you look at this list, “Well what about, there’s other things about food, where’s spiciness? How come we don’t have a spicy gustatory cell?” and we don’t have a spicy gustatory cell.

So what’s happening with spiciness is that it’s actually triggering some of the other receptors that you have in your tongue. So the receptors we talked about on the skin, you have those on your tongue as well. You have pain receptors, if you’ve even bitten your tongue you’re certainly aware of that.

You also have thermoreceptors that tell you about temperature. Spicy foods stimulate these thermoreceptors, they actually make you feel hot. It makes these cells, it binds to these same receptors and makes you think that it’s hotter in your mouth. The opposite is true with things like menthol. Menthol interacts with thermoreceptors and makes your mouth feel colder.

As you know with spiciness, it also stimulates the pain receptors in your tongue, those same things. In peppers you have a substance called capsaicin and that can interact with thermoreceptors and it can also interact with pain receptors and that’s why something that’s too spicy will actually hurt.

OK so up in addition to the fact you have the other receptors in your tongue for things like temperature and pain, you also can feel things in your moth. So texture is an important part of sensing food. It’s not just about things that happen on the taste bud. And in addition to these other aspects, we have other senses that also influence our taste perception. So I mentioned in the previous video that our sense of smell has a strong relationship with our sense of taste. That’s because food that we eat, the molecules waft up the back of the throat and they interact with our olfactory system. You can try to stop this by blocking your nose, right?

If you block your nose the air can no longer move up to the back of the throat. So that does a pretty good job of blocking it but it doesn’t block it completely. But you might be surprised that actually many of your other senses also play a role in this. So your sense of sight, your vision heavily influences taste and people can be fooled by mis-coloring foods.

So you can take jello that’s a particular flavor color it different colors and people will eat a bunch of different colors, all the same flavor, and they’ll actually think that each of them is a different flavor. I’ll post a link in the video description where you can see a video of this task where kids and adults were given lemon flavored jello but if it was colored red they thought it was berry, if it was colored yellow they thought it was lemon. It’s pretty interesting that we see this change, that our vision can influence.

Your sense of hearing can also influence through crunchiness of things. You can have people wear headphones that make foods sound crunchier than they are, like potato chips, and people will actually enjoy the chips more when they hear this extra sound. They don’t realize that it’s coming from the headphones but they think that the chips are actually crispier.

Finally our beliefs and our expectations play a role in our sense of taste. The things that we think about the foods we eat actually influence how they taste. So we can be fooled. If we think a wine is a very expensive wine we might tend to think it actually tastes better. Not just think it tastes better, we actually perceive it tasting better.

Or in another link that I’ll put in the video description, we can give people water, give a bunch of people the same water but give them different expectations. If they think it’s tap water versus if they think it’s some fancy bottled water, they’ll actually experience it tasting different.

OK that’s all for taste. I hope you found this helpful, if so, please like the video and subscribe to the channel for more.

Thanks for watching!