Welcome to this tutorial on the chemical senses. The chemical senses pertain to a set of special sensory systems associated with the head region of the body. And we are going to discuss them in several parts. In this part I'd like to give you an overview of the chemical senses. And this discussion about chemical sensation is going to again, illustrate for you the complexity of the brain as the body's most complex organ. And as we get into our special sensory systems for the chemical senses , we'll see once again evidence of genetically determined circuits that provide the foundation for the functions of the nervous system. And when it comes to discussion of these chemical sensory systems, I think we'll see some, some really remarkable examples of where there is genetic expression. In space and time that influences the structure of circuitry that provides for, in this case, the foundation for chemical sensation. So, I have just a brief tutorial for you. In this particular part, you will provide an overview of the chemical senses. And my goal for you, is that you'd be able to summarize the organization of the neural systems for the chemical senses. So, let's get started. And just a simple comment that will set the stage for our more detailed studies of olfaction gestation, in just a bit. Our chemical senses are special sensory systems primarily in the face, but also in the cavities within the head. And these are systems that detect minute quantities of chemical molecules in the environment. And these chemicals can serve a variety of purposes. And that's what I want to help you understand in this brief overview. So, consider, for example first, airborne molecules. So, the air is full of odorants full of molecules that have a particular shape and structure to them, particular chemical qualities. And there are specializations of receptors in the face and in the head that interact with these airborne molecules. Specifically, these airborne molecules interact with receptors that produce a sense of smell. And this is what we call olfactions. So olfactory sensations, are a response to the presence of these airborne molecules. Now some of these molecules, can actually produce irritation to tissues in the body. They are potentially damaging. And it makes great sense that we would have a chemical sensory system that would be dedicated to detect these potentially irritant molecules. And that's where the third major chemical sensory system comes in. It's called the trigeminal chemosensory system. Now in addition to airborne molecules, of course there are molecules that are mostly water soluble, and also lipid soluble that we ingest. So we put these molecules into our bodies, obviously through our mouth, and these molecules have an opportunity then to interact with the mucosa that is present in our oral pharynx. So as we interact with these ingested molecules these molecules can then activate a variety of receptors that give rise to our sensation of taste. This is what we call gustation. So ingested molecules give rise to gustatory sensations. Now, you may be wondering about flavor. Which, as we'll talk about as we move along here, is actually a combination, of, really all three of these chemo sensory pathways, when we think about it. Consider for example eating your favorite spicy food. There's a particular smell that might first arouse our appetite when this plate of food is presented to us. And then of course, as we begin to eat it, there is the consumption of these molecules that we begin to ingest and then begin to interact with our gustatory receptors. But, if it's spicy, there my also be a mild irritant quality to it that can drive sensations through our trigeminal chemosensory system. And somewhere in the brain, and I'll tell you where we think it actually happens in just a little while. These various sensory systems are combined. And they are combined in a sense that gives us our quality that we call flavor. Well, in addition to feeding behaviors these chemical sensory systems provide really a number of important functions. beginning with nutrition. So, these chemical sensory systems allow us to assess the palatability, or the desirability of those foods and drinks that we consume. and this is quite important as I think we all can appreciate perhaps not so much in our, our modern societies, but certainly, as we sample the foods of the world, wherever we may be, we are always on guard, are we not, for the palatability of food. trying to avoid potentially harmful substances. There are a variety of physiological functions that are regulated by our chemo sensory systems. these include memory, visceral motor behavior, reproductive cycles. And very importantly infant paternal behaviors and infant maternal behaviors. There are a variety of social interactions that are mediated via the chemical senses. Through the chemical senses we evaluate self and we evaluate others. As I mentioned already, safety becomes an important domain of chemical sensation. Not just for the ingestion of potentially harmful substances, but also our interaction with volatile chemicals in the environment. That might be mildly irritating at low concentrations, and potentially quite harmful at higher concentrations. And then lastly, it's through the chemical senses that so much of our hedonic rewards system is tuned. And what I mean by this is, those chemical messages. That either we ingest, or that we sniff, or that we otherwise interact with, with our chemo sensory systems. That can drive a sense of pleasure. And one can imagine lots of examples of this, an attractive perfume the scent of your favorite flower pleasurable foods and drinks. And quite interestingly, also the possibility of there being, pheromones. Now, as I'll describe as we get a little deeper into olfaction we know that, the old world primates, including humans, lack the specializations, in the olfactory epithelium, and in the peripheral parts of the olfactory system. To be sensitive to pheromones in the way that non old world primates and other non-primate mammals may be. but nevertheless there is some tantalizing bit of evidence to suggest that our behaviors are in fact influenced by chemical messages in a way that would be consistent with pheromone interaction. So, that will be an interesting discussion to bang around perhaps on the discussion forum or elsewhere. Well, I hope you've enjoyed this brief overview of where we're going to go over the next couple of pieces to this tutorial on the chemical senses. And I look forward picking up with you, in just a moment, in a discussion of the olfactory system. So, I'll see you then. [BLANK_AUDIO]