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Smell (Olfaction) – Other Senses (PSY, BIO)

by Tarry Ahuja, MD
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    00:01 Now, next sent -- sorry, next sense which would be scent is smell.

    00:06 So how do you smell things? And we call that the process of olfaction.

    00:11 So this one’s also quite unique and then it employs, again, detection of a chemical stimulus.

    00:18 So the olfactory receptors are found on the roof of the nasal cavity or the nasopharynx.

    00:23 And there is something called the mucus membrane there.

    00:27 So the mucus membrane like the name kind of applies.

    00:29 Mucus is we all know of kind of phlegmy or sticky.

    00:32 And the membrane is a body where things would stick.

    00:36 So as we breathe smells in, the chemical is actually end up sticking to the mucus membrane that’s found in the nasal cavity, and that allows the molecules to actually interact with the receptors that are found there.

    00:49 So olfactory nerves project directly from the olfactory bulbs of the brain in the temporal lobe.

    00:54 So it’s a direct connection.

    00:56 So very, very fast and it’s very, very hands on.

    01:01 There’s this limbic system in this area within the temporal lobe is an area that also deals with memory and emotion, which is why we tend to make that correlation between smells and memories and emotions.

    01:14 Now you go to your local fancy-pancy shop with your wife or girlfriend and they have all these different scented candles and they have different names like calming and romance and you know and basically what they’re doing is they’re linking that scent to emotions that most of us have.

    01:30 Now you can think of certain smells that evoke the smell and memories associated with, say, Christmas or maybe the beach or summertime.

    01:40 All of these different relationships are done in this area, the temporal lobe.

    01:43 So another really neat thing that happens is this paring of information, right? So the way I just said, you know, that smell equals Christmas.

    01:51 Well, how does that happen? So it’s not that you smell a rose and you automatically know that this equals rose.

    01:59 You need to make that actual cognitive connection.

    02:02 And so it’s a learned process.

    02:04 It’s based on experience.

    02:05 And so that’s why as we grow up and we interact with our environment, we smell different things, we know that, you know, a dirty poopy diaper stinks and a rose smells amazing.

    02:16 So how does that happen? Well, you kind of backtrack and think.

    02:19 Because when you’re a small baby, you really don’t know why you’re smelling.

    02:22 You haven’t made that association.

    02:24 But as parents, you’re changing a diaper and you open up the diaper and you see a nice gift for yourself and you’re like, “Oh my God!” And what’s the first thing you do? You don’t go. “That smells fantastic. Well done son.” Instead you’re like, “Oh my God, what a big pooh.” And you clean it up and you throw it away.

    02:38 Or if you walk by a garbage, a dumpster, what do you say? You don’t say, “The smell is amazing.” Usually, you make that connotation, “Well, this is gross.” And so over time, over experience, you learn that based on that experience, you make that connection and that is how we cognitively associate sense with memory and emotion.

    02:57 Another really unique thing is something called pheromones.

    03:00 And these are targeted chemical signals used to cause a social response within a species.

    03:05 So in English, what I’m saying is we all heard the term before pheromones.

    03:08 Certain animals release them. Human release them.

    03:11 And these are specifically designed to evoke a response out of somebody within your species.

    03:18 So sometimes we’re not even aware of it, but humans, as humans, we do release pheromones.

    03:24 And, you know, the idea is to attract the opposite sex.

    03:28 And you want them to -- usually, unconsciously you say, “Oh, you know I am attracted to you.” And part of that is controlled by your influence by pheromones.

    03:38 In animals, it’s a little bit more obvious where they literally on purpose release certain things, scents and pheromones to say, “Hey, it’s mating time, let’s go. I know you like this.” And they start spraying pheromones and scents.

    03:50 And the receiving animal will know that this animal is ready to mate and is ready to kind of procreate.

    03:57 So very, very targeted, very, very specific, but highly accurate.

    04:03 And based on that reaction within a species, you can see that’s a social response, right? So it’s going to determine socially what’s happening in response to that pheromone.

    04:12 So different cultures might have different responses to different pheromones.

    04:16 So again, it’s quite individual and it’s culturally based.

    04:22 Here’s an image that’s going to look at that specific process that I just outlined.

    04:27 So here our friend with no hair is smelling a rose.

    04:30 And you can see that the chemical molecules are going up into the nasal cavity and they’re sticking to the mucus membrane.

    04:37 And then the olfactory bulb, which is in the nasal cavity, you have these molecules activating the receptors.

    04:44 The receptors then go on to send an electrical signal and then that goes on to the parts of the nervous system that are going to the central nervous system that are going to process that smell.


    About the Lecture

    The lecture Smell (Olfaction) – Other Senses (PSY, BIO) by Tarry Ahuja, MD is from the course Sensing the Environment.


    Included Quiz Questions

    1. Roof of the nasopharynx
    2. Lateral wall of the nasopharynx
    3. Posterior aspect of the nasopharynx
    4. Torus tubarius of the nasopharynx
    5. Anterior aspect of the nasopharynx
    1. Taste
    2. Smell
    3. Sight
    4. Hearing
    5. Touch
    1. ...olfactory nerves relay signals to ganglions before synapsing in temporal lobe.
    2. ...is involved in perception of targeted chemical signals to cause a social response in a species.
    3. ...is connected with the limbic system.
    4. ...is linked to memory and emotion.
    5. ...olfactory receptors are located in the nasopharynx.

    Author of lecture Smell (Olfaction) – Other Senses (PSY, BIO)

     Tarry Ahuja, MD

    Tarry Ahuja, MD


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