Hello students, this lecture is going to be on gustation. We're going to be talking about taste. So gustation is the sense of taste and your ability to taste is related to your ability to smell. So appreciate that if you are eating something that food also whatever you're eating has molecules that might be in the air and those are also getting into your nose. And so both of those are happening at the same time. And so your brain puts those together as a whole experience. And so you get a perception with that. And so that that is related to your taste. And in fact, some tastes are are actually you perceive some tastes as taste, but they can actually be smells. And you'll get to study that in in lab. So again, make sure you do your if you can try to do the the taste and smell activities at home. You do not have to buy anything. Just use things that are similar for like sweet and salty and protein and things like that. So for gustation again this is the sense of taste. We are using uh your body uses chemo receptors. We're detecting chemicals in our foods or the things we ingest. And these are going to be through specialized receptors called taste buds. Taste buds are in or are part of your taste pill. So the bumps on the tongue are not really taste buds. They're actually taste pill and they are lined with taste buds. Every taste bud has all of the different types of taste cells to detect the different types of taste. And then your perception of taste is a combination of all of those different taste cells that are being activated at any particular time and a combination of smells. So if we take these bumps on the tongue and we blow them up and you can see here we've taken the bumps and then we are we are literally um showing the different taste buds on the side. So this is the taste bud. So all these different cells in here and you're going to have different taste cells. You're also going to have basil cells like you had in the respiratory epithelium. um and your your support cells and the basil cells will replace the taste cells just like they did in the in the olfactory epithelium. And you're going to have taste hairs kind of like the celia on the olfactory epithelium. The difference is these taste cells are separate from their sensory neurons. They look like they might be part of but they are actually separate cells. So these taste cells are are not directly they are not part of the sensory neuron. They are a separate cell. And so we will have this taste cell will have to create a we'll have to release neurotransmitter onto the sensory neuron to create an action potential in the sensory neuron for taste transduction. Okay. So our sense of taste is the conversion of chemical signal to an action potential. That will be the transduction process. And we have five classes of chemicals that we we can detect. Sweet, sour, salty, bitter and umami. When we talk about sweet, this is detecting simple sugar. So, glucose, fructose, um, galactose. There are some other chemicals like lead and ethylene glycol that have sweet taste as well that will bind. Um, and you know, babies, kids will like this because they taste sweet. Sweet um, sweet is attractive to us because it is a signal for energy. And so it is something that we typically like. And so sweet tastes that we have. So we have sweet receptors um or sweet taste cells. We have sour taste cells. These are detecting hydrogen ions. And you'll find these in in acidic things like um citric acid, lemon juice, um things like that. And then salty is detecting metal ions like sodium and potassium. So salt, light salt. Bitter is usually nitrogen containing compounds. Um alkyoid type substances. And this is our most sensitive taste cell. So the smallest amount is is usually it detects the smallest amounts or the most sensitive. And this is for detecting um bad things. So this is ve a very important taste cell because you want to pick up that something is not quite right. So salty is good because we we need our metals right. Hydrogen ion is good because hydro like sour things usually contain vit vitamins that are important like vitamin C and sweet obviously carbs are important. bitter because it's bad and um umami is the savory and this is be these things are like amino acids and so these are detecting proteins. So a lot of the taste cells are detecting things that we need in our body and we're attracted to those things because there are things that we need. Um, interestingly enough, there are people um that are called super tasters. And so there is a a a drug called proprioil that some people cannot taste it and some people find it very bitter and some people find it extremely awful. And um this is they're called super tasters. And these super tasters um may have more taste buds or they're just able to detect tech take detect better. But um this can be a good thing, but it can also be a bad thing because they may not want to take in certain foods and this could put them at risk for certain health problems, but they may avoid um certain types of foods. Anyway, I thought that was interesting. So, how does taste transduction occur? We have to take this chemical and we have to turn it into an action potential in our sensory neuron. So, how do how does how does this happen? Well, every taste cell is different. I only want you to be able to tell me how one taste cell in general can create an action potential. You don't have to tell me all of them. Note also, you don't have to give me the specific neurotransmitters because they differ for every every taste cell. So you don't have to you don't have to give them to me. We're going to try to be very simple here. Okay. I want you to just give me a basic understanding. So again, we have to have the chemical dissolve in the saliva. Right? So that's very important. So we need a moist mouth. that the mouse mouth is dry for whatever reason. Um, some disorders will cause a dry mouth and excessive sympathetic stimulation or certain drugs and that could affect the ability to taste. And so we the chemical gets dissolved and it will bind um a a receptor or it will come through an ion channel if it is detecting an ion. It depends on the type of taste cell. So whether it's an ion coming in or it is a it is binding a receptor. If it binds a receptor it activates a groin cascade. If it is an ion coming in then that stimulates um that causes depolarization. either the G-proin cascade causes depolarization or the ion coming in causes depolarization. Either way, you get a local potential. The local potential can then be transmitted along the membrane and that will cause voltage gate voltage gated calcium channels to open that will stimulate the influx of calcium. Influx of calcium stimulates the release of neurotransmitter and then that neurotransmitter will then activate the sensory neuron on the other side and stimulate an action potential if we reach threshold. So how does that work? So here is an example of a taste cell for salty or sour. So this is for salty or sour. Note, this would be different for all the other taste cells. For umami, for sweet, and for bitter, they use a G-proin. So, picture a um re a protein receptor. A chemical binds a G-proin. The G-proin cascade occurs and we're going to get some sort of cascade. It's going to be different depending on what's going on. And then we get a local potential. Okay. And again, it's a local potential. That's so important. Don't forget this. Okay. And so in this taste cell, the presence of the hydrogen or the or the sodium or potassium, the ion actually comes through the channel. So the more you have, the more that comes through. Sodium or hydrogen ions come through. So they're not necessarily binding, but they're actually coming in. The more that comes in, the more depolarization we get. We get a local potential and that local potential propagates along the membrane. We do not need an action potential. This is a very small cell. So short distance is fine and this causes voltage gated calcium channels to open. Calcium influx occurs. Calcium moves in down its gradient. This signals the release of synaptic vessels. We've seen this before. That is the signal for synaptic release of vesicles. And we release neurotransmitter. You don't have to tell me what the transmitter is, okay? They vary on all the different taste cells. So don't don't bother. That neurotransmitter will then bind the sensory neuron and create an action potential in the sensory neuron. Now we can start transmission. All right. So what is our gustatory pathway? What is the pathway for um gust gustatory um sensation that action potential will be propagated along the sensory neuron depending on the location of the taste the taste buds and taste cells. So if it's the if it's the anterior third of the tongue it'll be propagated along cranial nerve 7. If it's the posterior um anterior two/3s, if it's the posterior third, it'll be propagated along um cranial nerve nine. So, facial nerve, glossophrenial nerve. If it's in the fairings in the taste buds that are in the back of the throat, um it will be on the vagus nerve. So, we have action potentials propagating along these nerves going to um the solitary nucleus in the medulla. From there, we'll synapse on cell bodies of the next neuron which will propagate an action potential to the phalamus. At the phalamus, we synapse on a cell body and that will propagate an action potential to the primary gustatory cortex in the pietal lobe and um also the insula. You can add an insula here. It um they do both. So um from there we're going to go to all sorts of places. We're going to go to the prefrontal area. We're going to go to the lyic system. Remember taste is associated with memory and emotion. You can taste something and feel very strongly about it and have memories about it. You taste your grandma's cookies. You remember cook, you know, being in her kitchen and you um you have fond memories of that and you feel good. Um you can taste something bad, right? and have a bad memory. It's highly highly associated with emotion and memory. And so we'll go to the lyic system. We're going to go all over and associate. But you just need to get me here. Primary gustatory cortex, parietal lobe, and insula. So that's it. So here we're traveling along these three nerves depending on the location and we're going to synapse at the solitary nucleus. Think solitary T for taste in the solitary nucleus and then we're going to go to the phalamus and then to the primary gustatory cortex. Okay. And that's it for gustation. Our next lecture is going to be on the anatomy of the eye and then we'll get into the transduction of vision and then um the transmission of vision. All right, I will see you there.