 So taste, my friends, is a chemical sensation. So taste cells, which are sensitive or deliver information about what you are tasting, taste cells are chemo receptors. And most people think of taste cells, you actually think of taste buds as being what you taste with, right? Most of us think of our taste buds as actually being the little bumps on your tongue. The fact is that there are like a million taste buds, I don't know what the actual number is, embedded in the bump on your tongue, which is called a papilla. This is an image of different taste cells embedded in a single taste bud. So this is a taste bud right here. I'm going to trace a single taste cell so you can see that how it's kind of set up here. A taste cell has, it's long, and it touches this pore, this is called your taste pore, which is open to your mouth. You can consider this the space or the lumen, and so you have, your taste cells are open to that space. If you start thinking about it, that pore, that taste pore is tiny. Nonetheless, if you eat something, little pieces of what you eat actually fall into the taste pore and activate the cell. So first thing I want to do is draw you a picture of a taste cell. This is what it looks like. Now, the taste cell is actually, I don't know, how do we want to say this? It's not a neuron. And we've got a couple of different kinds of taste cells. I'm going to draw one kind first. What I know is that on these little, these are actually microvilli. Embedded on these microvilli are sensory receptors. And here's the deal. Each taste cell has one flavor of sensory receptor. And that sensory receptor is going to bind to some kind of molecule. I say that each one has one kind. They're actually, they think, at the last publishing of the book that I used, there are 13 receptors. So 13 different possible receptors that molecules can bind to. Now think about that for a second. That means basically there are 13 different flavors. And then it's the combination of how those 13 different receptors are stimulated that delivers kind of rich, unique sensations of flavor to our brain. Even though there are 13 different receptors that they've found, there are only five primary sensations of taste. And I'm going to show you what that means because look at me being really careful. That's an actual taste bud. And look at those cells. We're going to see how those guys work. But first of all, I want you to see our different flavors of receptor that pick up taste. Our basic tastes, even though there are 13 of these things, our basic tastes are salty, sweet, sour, bitter, and umami. Umami, there's no way I can describe it. It's like MSG. I can't describe that either. Is that salty? It's not salty because it doesn't fall into the salty category. It's unique. Some of you will know what I'm talking about. But that's it. Like all of our receptors can fall into one of those five taste categories. And here's the crazy thing. The message, the mechanism by which salty molecules deliver the message of, oh, that was salty to your brain, is different than the mechanism by which bitter ones send the message to your brain. And let's talk about what is this mechanism you speak of. Are you ready? Okay, first of all, we're going to do salty and sour. So let's do it like a, like a, this, salty and sour. This is the mechanism by which the information travels or is delivered. First of all, a salty or sour molecule binds to the receptor. Second of all, an action potential. What is generated in this receptor cell? Dude, does that make this thing a neuron? I don't know. Action potential is generated, guess what? Here comes the action potential. What happens when it reaches the end of this thing? Yeah, this is not a nucleus. This is a bubble of serotonin. We think of serotonin as our feel-good molecule. Well, it is also involved in sensations of taste, in sensations of salty and sour taste. So serotonin is then exocytosed into the synapse. So that would be step, what, three? Exocytosis of serotonin. And then serotonin stimulates a neuron. Okay, what color is my neuron going to be? It's, we'll make it an afferent neuron, which I usually make those guys blue. So I was trying to think of, how am I going to draw my neuron like this? And we're going to go to the CNS through olfactory nerve, cranial nerve one. This is CNS. Okay, so you barf serotonin on to an olfactory nerve, and that olfactory nerve gets the message, sends an action potential to the brain. Fantastic. That one makes sense, doesn't it? Okay, watch this one. I'm going to give it a different color slightly so that you can appreciate the fact that, you know what, this is a different flavored receptor. I mean, yeah, chemo receptor. It's a different flavored taste cell. And so we're going to pick up different kinds of sensory stimuli. So let's just do that. We'll make them round this time. So this, you can see it's still a taste cell, but it just has a different flavor. It's only going to pick up the round orange molecule. The pink square molecule is going to bounce right off that thing. You're not even going to see it. The orange round molecule is going to bind. Now, here's what happens. So this is everybody else. This is bitter, umami, and sweet. This is so cool. First of all, the molecule lines, just like we would expect. Second of all, I'm going to give you a hint. Look at what happens. We get a second messenger cascade. And you can think about, why would you do that? What are some possible functional consequences of that? The second messenger cascade, this is really interesting, results in the production of ATP, which comes out of the cell and stimulates my next neuron. Now, once it stimulates the neuron, same mechanism. Now we're going to the CNS, to the central nervous system, to process that sensation of smell. But the significant thing is that we have two different mechanisms for receiving sensations of taste. All right. You can have a wakadouzi receptor. And if you do, that means you can't taste that thing. Just like that. And you can have a wakadouzi chemical receptor, like a little protein receptor, is wakadouzi. I don't know if you can have a whole kind of taste cell that is not functional. How cool is that? All right. So that's how taste works. Let's talk about how smell works.