Source: Video and Images Created by Amanda Soderlind
Welcome to this lesson today on taste and smell. We will be discussing taste and smell as chemical senses. So when I discuss taste and smell as a chemical sense, what that means is that in order for our brain to be able to interpret a taste or smell, it has to interpret the chemical makeup of the substance that makes the taste or the smell. So chemoreceptors are the receptors that receive sensory information about taste and smell and then relay that information to your cerebral cortex for interpretation.
So we're going to start by discussing taste first. So the technical term for taste is gustation. So we have taste buds scattered within our mouth that contain taste receptors. And these taste buds are on our tongue, on the sides of our cheeks, on the roof of our mouth, in our throat. So these taste buds are scattered all over in our mouth, not just on our tongue, as some people would believe.
So what happens is that saliva will enter the pore of a taste bud and come in contact with these taste receptors. And then those receptors will stimulate a sensory neuron. And the sensory neuron will relay that information to your brain.
So the five common tastes or the five primary tastes that we have are sweet, salty, bitter, sour, and umami. Now you might be familiar with those first four. You can think of something that's sweet tasting, salty, bitter, or sour. But umami is something that you may not have heard of before. So basically, this taste describes something that is savory, so a savory taste we describe as umami.
And flavor, when you taste something and it has a distinct flavor, that flavor can be the combination of those five tastes or any combination of those five tastes. So maybe it's a combination of sweet and bitter or salty and sour and sweet. So it can be a combination of any of those.
An important part of taste is smell. So input of information from olfactory receptors influences the flavor of something. So that's why if you've had a head cold, for example, you can't taste your food as well, because if your nose is stuffed up, you're not getting that input from olfactory receptors. And therefore, it dulls the taste or the flavor of that food. So taste and smell are very, very closely linked. In order to be able to taste things, we need to be able to smell.
So that leads us to our next chemical sense, which is smell. And the technical term for smell is olfaction. So olfactory receptors located in our nose detect substances that are vaporized or water soluble. So when we smell something, we're smelling something that's vaporized or water soluble. And those olfactory receptors located in our nasal cavity are able to detect that.
So the odor molecules will them attach to those receptors in the nose of the olfactory epithelium. So it's a layer of tissue in your nasal cavity. And then those neurons will become stimulated. And nerve impulses will travel to the olfactory bulbs in the brain.
And then from there, the signal is forwarded to the cerebral cortex, where your brain will then interpret what the smell is. Is it lemon? Is it a pine tree? Is it cotton candy? What is that smell?
So we're going to take a look at some diagrams here just to give you a little bit better idea of how taste and smell work at the cellular level. So we'll take a diagram here. And we're going to look at this part of it first. So this is kind of describing taste.
So we have a picture of a tongue right here. And as I mentioned, we have the five main categories of taste. So I'm going to kind of label where those are on the tongue here. So on the sides of the tongue, we have sour, so this is where we can--
And then we have sweet on the tip of the tongue. We have bitter towards the back of the tongue. And then we have salty. That kind of goes along the edges around the front of the tongue.
So this picture showing us a close up of a part of the tongue right here. And I'm actually, I think, going to zoom in just so we can see this a little bit better. There we go.
So if we were to zoom in right here, we're zooming in to a part of the tongue where we can see the pores. So as I mentioned, saliva will enter these pores and come in contact with the taste buds. So we have our taste buds here.
And then if we were to zoom in even more on one of our taste buds, we're going to identify the parts of that. So our taste buds are made up of these taste cells. So you'll notice the individual cells here with the nuclei. And then we have our taste pore, and then our sensory nerves. And these sensory nerves will relay that information, the incoming information about the taste or the flavor, to the brain.
So now let's take a look at our next diagram down here about smell. So down underneath here is where we would have the nasal cavity. So if you were to inhale, you were to smell, the vaporized substance or the water soluble substance would enter through your nasal cavity. And then we have our smell receptors right here.
So basically, the odor molecules would attach to those smell receptors. And those smell receptors go up and they connect with the olfactory bulb in the brain. And the olfactory nerves within the olfactory bulb will then carry that information up towards your cerebral cortex. So this is the olfactory nerve. And then we also have our olfactory epithelium. And the olfactory epithelium is just that tissue that lines the nasal cavity where the smell receptors are located.
So this lesson has been an overview on taste and smell as chemical senses.
A perception of taste triggered by amino acids and is often associated with savory foods (example: meat).
A perception of taste often associated with spoiled or undesirable foods (examples: sour milk, nicotine).
A perception of taste triggered by acidic foods (example: citrus fruits).
Foods that are rich in salts/minerals elicit the sensation of saltiness (sodium, calcium salts, etc).
Foods that are naturally rich in carbohydrates elicit the sensation of sweetness; there are also artificial compounds designed to stimulate sweetness (artificial sweeteners).
Encapsulated receptors found within taste buds; taste buds are located on lingual papillae on the tongue, in the roof of the mouth and your throat; there are 5 different tastes that human taste buds are capable of detecting.
Receptors embedded within the mucous membranes of the nose that are specialized in detecting odor molecules/various odors; encapuslated nerves that synapse with the olfactory bulb on the superior/upper aspect of the roof of the nose.
Special senses that are detected by highly specialized, chemical receptors (olfaction and gustation) that detect dissolved chemicals and gases; olfactory and gustation receptors are encapsulated nerve endings that are embedded with mucous membranes (olfactory) or muscle & epithelial tissues (gustation).