 Hey everybody, Dr. O here. So in this video we're going to talk about gustation or taste. So taste begins in what are called taste buds. You've probably heard of them. So taste buds are going to be where the taste receptors or gustatory receptors are. But they're going to be in these epithelial projections that are called your lingual papilla. So there are really four types here, probably only three of them are really important though. Let's start with the filiform or phyliform papillae. They're just there to provide friction. They don't actually have any taste buds in them. Next we have the fungiform papilla. They usually have about five taste buds in each one of these epithelial projections. Then we have the circumvalate papilla. There can be as many as a hundred taste buds in one of these. Then lastly we have the foliate papilla. Not really that big of a deal. They're generally just found on the side and the back of the tongue. So those are the epithelial projections called lingual papilla where your taste buds are going to be. So here we see a taste bud. It's going to have basal cells or stem cells that these gustatory cells are generally only survive about 10 days and they have to be replaced. So there's a source of stem cells there. And then you do have the gustatory cell which projects these taste hairs up through the taste pour at the top. And that's going to be where taste actually occurs. As far as like the different taste sensations we have, what's known as gustatory discrimination, the four primary taste sensations are called sweet, salty, sour and bitter. There is some evidence that our tongue is more sensitive to those taste sensations in different locations. But generally speaking all your taste receptors respond to all of them. Again there is some evidence that the front of the tongue or the anterior tongue responds more to salty or sweet and the posterior tongue responds more to sour and bitter. But there really isn't a difference between the taste receptors. If we seem to be the most sensitive to bitter and that actually makes sense from an evolutionary standpoint, if something is bitter it's probably poisonous and should be avoided. So bitter is there basically to warn us of poisons and things to not eat. Sweet is generally reminding our brain that there's a good source of calories and quick energy here. Sweet is basically a mineral sensor. So it senses mineral content and food to make sure we're getting minerals and don't die. And honestly it's pretty unclear why we have sour receptors. I can't answer that. I know that my kids like sour candy but there's really an evolutionary advantage there. At least not that I know of. So those are your four primary taste sensations, sweet, salty, sour and bitter. But there actually humans do actually have two more. And that is umami which is a savory receptor. I think of things like Parmesan cheese, chicken broth, these would be the types of foods that trigger these receptors the most. It actually is triggered by the amino acid glutamate. So it's actually a protein sensor. So we have a sweet sensor that tells us about sugar and carbohydrates. We have a salty sensor that tells us about mineral content. And then this umami will tell us about the protein content of food potentially. And lastly you would have water receptors. So we don't think of water having a taste but we do have water receptors, most of them being in the fairings there in your throat. So sweet, salty, sour, bitter, umami and water would be the six taste sensations we'll talk about in this class. Alright so actual taste sensations. So just like with smell or olfaction, these taste hairs only work if dissolved chemicals come into contact with them. Which is why your mouth and nose need to stay moist and wet in order for smell and taste to work properly. So when these taste hairs are triggered by something that's going to lead to a release of neurotransmitters and that's going to send information down your sensory nerves here. So we're talking about taste here. We'll come back and talk about flavor in just a moment. But in the end these gustatory pathways are going to be linked to cranial nerves 7 and 9. Hopefully you remember from our earlier unit that cranial nerve 7, the facial nerve controls the anterior two thirds of the tongue. Cranial nerve 9, glasopharyngeal, controls the posterior third of the tongue. So this information is going to travel down cranial nerve 7 and 9 where it's going to reach the medulla langata, the thalamus and then finally to your taste cortex or gustatory cortex which is in the insula or insular lobe which you really can't see here. You have to appeal the frontal and temporal lobes apart to get to the gustatory lobe. All right but now let's talk a little bit about flavor because gustatory or taste sensations are more powerful when they're associated with smell and other sensations to be completely honest. So what you're looking at here is this idea of flavor. So flavor is going to be taste plus smell. You can make a very strong argument that 90% of the flavor of food is actually coming from smell. So the foods we eat have these dissolved volatile compounds that impact the flavor of what we're tasting, not just the taste. So the taste would be about 10% of it, flavor is going to be all the other things that can impact it. So an example is like a tomato has 200 volatile compounds that make it taste good because of how it's smelling, not exactly how it's tasting and this would be why you probably like tomatoes you grow yourself or tomatoes that are grown in nutrient rich soil are going to have more of these compounds and they are going to have a better flavor. Flavor being the key word there. The reason I want to show you this picture is because a big part of what we're smelling that impacts flavor is called retronasal olfaction. So yes you smell a food before you put it in your mouth but when you put a food in your mouth and start chewing it a lot of the smell actually travels up through the throat and up to the back of the nasal cavity. So you're smelling things from inside of your mouth actually and then of course mouth feel, sight, all these things are going to impact the flavor of food as well but olfaction or smell is dominant when it comes to flavor. So taste is taste, flavor is taste plus everything else that impacts how you feel about that food especially smell. All right so that is gustation or taste. I hope this helps. Have a wonderful day. Be blessed.