In this video I explain the process of transduction for scent; how odorant molecules in the air can trigger different olfactory receptor neurons which then send messages to the rhinencephalon or “nose brain”. I mention the links between scent, emotion, and memory and how pheromones allow for chemical communication between members of a species. Finally I mention the relationship between scent and taste, which will be further explained in the next video.

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Video Transcript:

Hi, I’m Michael Corayer and this is Psych Exam Review.

In this video we’re going to look at olfaction, or our sense of smell. So how do we smell things? What exactly is happening when you smell something?

The way that we smell things is that we use special cells, which are chemoreceptors that interact with chemicals. In the case of smell we use olfactory receptor neurons. These are neurons that are specialized for interacting with odorant molecules.

Odorant molecules are molecules that float through the air off of the objects that we smell and they go up our nose and they interact with these receptor neurons. So we have about 10,000,000 of these olfactory receptor neurons and they come in different types. We have about 350 different types of olfactory receptor neurons so different molecules will stimulate different olfactory receptor neurons and this allows us to smell different things.

Now of course we can smelll more than 350 different things because the things that we smell are complex. They’re releasing a bunch of different molecules and so the unique pattern of interactions that this group of molecules triggers will gives us the unique scents that we experience.

So let’s look at a diagram of this. We can see that this flower here is releasing some pattern of molecules and those are wafting up here, going up the nose and they’re going to interact with these olfactory receptor neurons.

Now it’s kind of interesting to think about this, that when you smell something, you’re really interacting with actual molecules from that thing. So this is fine when you think about a flower or you think about a freshly baked apple pie, right? That apple pie is releasing molecules out into the air, they’re floating around in the room and then they go up your nose and interact with your body. It’s a little bit less pleasant when you realize that the same is true for bad smells. So if you walk into a bathroom and it smells really bad in there there’s molecules of those things floating around in the air, they’re actually going inside your body and interacting with some of your neurons.

Ok, so let’s go back to our flower example, a little more pleasant here. So this flower releases this unique pattern of molecules and it reaches this olfactory epithelium and here there’s a layer of mucus. This mucus sort of dissolves the molecules and allows them to interact with the olfactory receptor neurons.

Then depending on which olfactory receptor neurons are stimulated they’re going to stimulate these other cells called glomeruli and this comes from the Latin for “little balls of yarn” and that’s because these are little tangled looking cells. So a certain pattern of ORN activation will stimulate a certain group of these glomeruli and these then send their messages from the olfactory bulb to an area of the brain where they’re processed.

The area of the brain where this processing occurs is called the rhinencephalon. And this literally means “nose brain”. So this is the area of the brain that processes this olfactory information. It’s kind of unique in that all of our other senses the information first goes to the thalamus and then gets projected out to the cortex but in the case of scent we have this immediate connection between the olfactory bulb and the brain.

This area of the brain, the rhinencephalon, is linked to the limbic system. This is responsible for emotion and memory. This explains this connection we have between certain scents and emotions and memories.

You’ve probably had the experience where a particular scent will immediately remind you of something or immediately trigger some emotional response. If we think about our evolutionary past it makes sense to think that the scent of a predator we might want that to immediately trigger a particular emotion.

Now it’s possible to lose your sense of smell or to never have it in the first place. This is called anosmia. This can happen either because you’re born this way or you could have damage to your rhinencephalon or you could have damage to your olfactory receptor neurons so that they don’t function properly anymore. This would prevent you from being able to smell.

Other animals have an additional olfactory system and this is called an auxiliary olfactory system and this allows them to detect pheromones. So what are pheromones? Pheromones are chemical messengers that are sent between members of a species.

Animals release pheromones and then other members of their species can detect these pheromones and this can influence their behavior. So often this is used in the context of mating. So animals will release particular pheromones and this will influence their mating behavior of other members of their species. Humans, however don’t have a specialized auxiliary olfactory system. But we can detect pheromones and humans do release pheromones and they can have some influence on behavior.

Now one example of this is that humans are actually able to detect kinship based on pheromones. In other words, particular smells, you can tell who’s related to you or not. Not exactly, you can’t smell something and say “Oh this is definitely my long lost brother!” but we can estimate some level of kinship based on smell and this is happening essentially unconsciously through these pheromones. Again, it’s not this conscious process of “this person smells like a second cousin and this person smells like an immediate family member” or anything like that. But there’s evidence that we can detect some degree of relatedness based on scent and based on pheromones.

OK the last thing I want to mention is the relationship between scent and taste. In the next video we’re going to talk about taste, we’ll see it’s very difficult to separate the two because when we smell food, the foods we eat are often releasing these odorant molecules and those are interacting here and then when we chew the food it’s also able to go up the back of the throat here, up here. And our sense is going to be sort of intrinsically linked to our sense of taste.

So we’ll see that in more detail in the next video. OK, I hope you found this helpful, if so please like the video and subscribe to the channel for more.

Thanks for watching!