Understanding the Human Senses

Okay, back to A&P 2. How excited are you? So this semester starts off with the special senses or just senses in general chapter. And so this ties a little bit into A&P 1 as far as we ended A&P 1 with the nervous system. And so this is going to have some of that. But don't worry if it's been a while since you had A&P 1. Anything that you need from A&P 1, I will completely review. So hopefully you'll remember it. But if you don't, you'll just have to. learn it again, no problem. So don't think you're behind. Nobody's behind. Okay, so the whole goal of senses is to link the external environment, so the outside world, to what's happening inside. So it all goes back to homeostasis. So if you didn't learn anything in A&P 1, hopefully you learned homeostasis, because that is the... number one idea of physiology. This is the underlying idea of physiology. So if you don't remember homeostasis, the reason I have this little picture here is homeostasis is maintaining balance. So it's basically maintaining control of the inside of your body. So the outside world is so crazy chaotic, especially right now, but your inside is very calm. So homeostasis is basically just maintaining that. balance. And so keeping your temperature balanced, even though it could be 80 degrees outside or negative 20 degrees outside, your body temperature is still around 98.6. So maintaining your breathing, your heart rate, your pH levels. So maintaining a constant internal environment is the nerdy definition of homeostasis. Maintaining a constant internal environment. So this chapter is about senses. So how can I control what's going on inside my body if I don't know what the heck's going on out there? So I have to make sure that I'm connected, that I know what the temperature is. How would I know if I'm supposed to sweat or shiver if I don't know what the outside temperature is? So there are different types of senses. So we have general senses that are located all over your body. So general, if you think of the word general, these are generally located all over your body. They're very, very simple. They're almost like little buttons that get pushed. So you have touch, pressure, vibration, pain, temperature, proprioception, which I do define on a slide coming up. I don't know why I don't put it on this one. So proprioception is knowing where you are in space. So like if you close your eyes and put your arms out to your sides. Like you know your arms are out to the side. I'm sitting in a chair right now. I know my feet are pointing down. Fluid pressure. So this can be in your ear, which affects balance. But also blood pressure. Like I know when I'm pissed off, right? Like I can feel that blood pressure surge. Then we have somatic. And so these general senses, whether you're talking touch pressure, vibration, temperature, whatever. These can be felt from two different places. Somatic versus visceral. So somatic means body. but that's not very helpful in anatomy school because everything is body, right? But somatic is body. What I think of with somatic is I think more of the surface of the body, more superficial things like your skin and your muscles, your tendons and your joints. So these are things that are kind of on the periphery of your body. So like the torso would be more the central part of your body, right? These are things that are giving you peripheral information. Like when you touch a hot stove, that's going to come somatically. versus visceral. If you remember the word viscera, viscera means organs. I call them ooey gooey squishy parts. And so viscera being the ooey gooey squishy parts, I need to know when my stomach is full. I need to know when my bladder is full and it's time to pee. You need to know when it's time to duty. You need to know when your heart's racing. So you need information from the organs themselves. So touch, pressure, vibration, pain, temperature, proprioception, fluid pressure, generally all over your body. But we talk about them more on the surface, somatically. Or we talk about them deep inside, visceral. Because it's a very different sensation, a mosquito walking on your skin, versus your stomach stretching because you just had a cheeseburger. God, a cheeseburger sounds good. So in A&P 1, we talked about general senses a little bit when we did the integumentary system, when we did the skin, because the skin has touch receptors and temperature receptors and everything else. But this semester, we more focus on special senses. And that's what our first two labs will be is special senses. So this is olfaction, which is smell. Gustation, which I think is a fun word, especially if you say gustation, is taste. So I always think that like gustate, like has taste kind of in the word, gustation. Sounds like taste almost, because otherwise that's a weird word. Vision, which is, of course, seeing things. And then your ear is in charge of both, of course, hearing and equilibrium. Equilibrium is balance. So instead of being all over the body, like the general senses, these are in very specific regions of the head. So your head does a lot of things, right? It's not like you can see with your toes or see with your elbows or smell or taste with your fingers. which would make restaurants weird. Okay. Imagine if you tasted with your toes. I mean, restaurants would be a whole different game. So these are things that are in the head and they're very complex. As we're going to see in lab. I mean, it is complicated to see. The eyeball is complicated, which shouldn't it be? I mean, seeing is complicated. Hearing is complicated. So anatomically, these guys are a bit of a nightmare. Okay, so to review, it's all about sending information to the brain and away from the brain. So these are like nerve superhighways. You touch the hot stove. You need that information to travel down your arm, up to your brain. Your brain decides, okay, how hot is it? Should I do something about it? And then the brain sends a signal to the muscles, so we now go back down to the arm, out to the hand, to jerk the hand away if it's hot, or leave the hand there if it's nice and warm and you like it. So it's just like kind of like Interstate 74 has the east and west lanes. We've got a two-way street here. So if you don't remember these terms, you may want to write them down. Corticospinal tract and spinothalamic tracts. These are like the east and west lanes of 74. These are the nerve pathways. These are the nerve superhighways that are going up your spinal cord to the brain and then bring back down the spinal cord and then out to the nerves. So corticospinal tract. Cortex, if you remember that word. If you don't. It's fine, but we're going to use it a lot this semester. Cortex is the surface of an organ. So this is the surface of your brain. So if you're going from the cortex to the spine, you're going down, obviously, right? You're going from the brain to the spinal cord. So information is going out. So we would call that efferent with an E. And the way that I remember that is I think E for exit. So this is the brain has made a decision and it's sending its response. So it's efferent. Another word we had from last semester is this would be a motor response because motor is movement so that's what the brain is doing it's causing movement. So corticospinal tract is going from the cortex the surface of the brain down your spine so it's leaving the brain So it's efferent, and it's a movement, so it's motor. The other one is bringing information to the brain. So this is going up the spine to the brain, and if you remember, there's that structure in the middle of the brain that's called the thalamus. So this is the spinothalamic tract. So it's going from the spine to the thalamus. That's obviously bringing information to the brain. So this is afferent with an A, just means to the brain or to the nervous system. And this is a sensation. So this is a sensory pathway. So these are your two pathways. You're either sensing things or you're motoring. You're either sensing or you're moving to respond to that sensation. So these are the two major tracks. So the function of all these receptors you have all over your body is to turn whatever stimulus it is, whether it's touch, temperature, pain, smell, pressure, whatever, into an action potential. So we did that in AMP1, and boy was that not just the best time of your life, okay? The nervous system, it rocks everybody's world with the whole acetylcholine opening the doors, the sodium can rush in, and you had to go from negative 70 to negative 60 millivolts, and it was crazy. So we've already done that. So I'm assuming you already know how nerves fire. You may not remember the details, but you've already took tests on that. So for this semester, we're basically just saying an action potential, which we had in AMP1, now we're just basically thinking, okay, the nerve's firing. So we need enough stimulus to cause threshold to be achieved. If you remember from AMP1, that meant we had to have enough doors open to let enough sodium in to get us from negative 70 to negative 60. We called that threshold. Again, though, for this semester, just think the nerve has to fire. You have to get enough. like stimulus to cause the nerves to fire. Some of the receptors in your body aren't very fancy. So they're just like little neurons. So I have this little picture of the neuron up there, if you don't remember the parts of the neurons. We have the little dendrites, so those are on the right side. The little dangly dendrites is how I always remember them. Dangly dendrites. So you have several of those. And then on the left, you have that one long axon. So most of the time, 99% of the time, the neurons have one axon. But there are exceptions that we're about to see. But a lot of these receptors, like I said, that are more like touch receptors, that are more like little buttons that get pushed, they kind of look like these little neurons. So they respond to the stimulus. The dendrites gather the information, and they send it away on the axon. So that's how I remember it, A and away, axon, away. So the whole point of a stimulus, whether it's temperature or pain, is to let us know there's a change in the environment. Because homeostasis tells me I have to maintain an internal happy place. I have to maintain this internal balance. Well, how can I do that if I can't react to the outside world? We always use temperature because it's so easy. But think about how many different temperatures you're exposed to on a daily basis. When it's summer and it's so hot outside you want to die, you walk inside and the air conditioning is sometimes so cold you need a sweater. Well, again, if I didn't know about that change, how would I know if I'm supposed to put on that sweater? How am I supposed to know if I'm supposed to sweat or shiver? So when the environment changes, that's when we got to know what's going on because we need to make a change. So this happens because those dendrites and the cell body, which is where the nucleus is, are going to get graded potentials. And if you don't remember that from AMP1, again, I'm not testing you over this again because we already did it. But that just meant that different parts of the neuron can be experiencing different stimulation. Kind of like a room. If you have a room with an air conditioner, if you're close to the window unit air conditioner, you're going to be really, really cold. If you're on the other side of the room, you might not even feel it. So if you think of that neuron, if one of the dendrites is picking up a stimulus, the other dendrites might not be affected at all. And so we call this a graded potential. We just need enough sodium to rush in. to cause us to get to threshold. We got to get, if you remember the axon hillock, which is like the little neck of the axon or right before the axon starts, it's like the neck of the neuron. We had to be at negative 60. So our whole goal though is to initiate these nerve impulses, afferent. So we're bringing things to the brain and spinal cord. That's the whole goal of sensation, right? What does it matter if you can touch a hot stove if you can't tell your brain it's hot? Like that's not going to work out. So we have to be able to send smell to our brain. We have to be able to send taste, temperature, pressure, all this information to our brain so our brain could decide what to do about it. So CNS is just central nervous system. We classify sensory receptors based on the stimulus that they respond to. So you do need to know these terms. So mechanoreceptors are responding to mechanical changes. So touch, if you touch something, it changes your tissue mechanically. pressure the fancy term for a pressure receptor is a baroreceptor so I always think barometers like for weather always talk about pressure changes with weather like the barometric pressure is doing this whatever vibration stretch body position which again that nerdy word is proprioception so on that previous slide I said I didn't define it this is when you close your eyes and stick your arms out you know where you are and hearing so all of these are mechanical changes to your body like the tissue is physically changing. Thermoreceptors, that one's easy. That's temperature. Photoreceptor, that one's easy. If you think photography, you need light, like nothing blinds you more than an iPhone camera, right? Chemoreceptors, chemo being chemicals. And when you hear chemicals, everybody gets all bent out of shape, like, oh my God, chemicals are so evil. But your whole body's chemicals. And this is why we can smell. So this is why olfaction happens and why we can taste, which taste is one of the best things ever, right? All because these chemicals dissolve. And then nociceptors are pain receptors. So the way that I remember this is I think nociceptors, I think Novocaine for pain, even though that really doesn't make sense, but that's just the stupid way I remember it. So pain can come from tissue damage. So you cut yourself or your dog bit you. Extreme temperature. Like, oh, don't we love Illinois? You go outside when it's so hot and you feel like your skin's frying, but then you also go out in those negative 25 wind chills where your nose hairs stick together. And that hurts just as much. Frostbite does not look like a good time. And then, of course, chemical damage. Like if you spilled phenol, the cadaver chemical, on you and left it on there too long. Or acid. Or bleach. So pain sucks, but it's very important for our body to know what's going on so we can make changes. Where does this information go? So once we go up that spinophthalmic tract, the part of your brain that receives this information is the postcentral gyrus, which if you don't remember that, we're gonna see it in lab. Again, we had this in AMP1. Those were those two strips on the brain. So the one that's highlighted there is the postcentral gyrus. The one in front of it is the precentral gyrus. And so if you look at this diagram, it says somatosensory cortex. That sounds hella fancy, but cortex just means surface. sensory is the information you're bringing in and somato remember just means body so this basically just means the surface of the brain getting all of the body's sensory information so i think of this like a cell phone tower when i call my mom it doesn't just go to her it goes to a cell phone tower and then to her so when you when you um sorry smell is different so smells the weird exception to this but every other sensation okay say i touch um a cold ice cube you That information is going to travel down my arm. It's going to go up the spinothalamic tract, and it's going to stop at this strip in the brain. And then that is going to be sent, from there on, it'll be sent to the region of the brain that deals with temperature. So it's just a stopping point for all the sensory information, except for smell, because smell is really strange. So once information has gone to that strip, the brain then sends it on to wherever deals with it. Just like that cell phone tower sends the signal to my mom's phone. So if you look at this little picture of the brain, we had this last semester, we had the lobes of the brain. So the frontal lobe is that kind of pinkish-orange color. It's the largest lobe of the brain. Now, this is not an important lobe for this chapter because your frontal lobe is why you have the personality you have. It's why I have my dazzling sense of humor. my sarcasm, my love of travel and pizza rolls. So your frontal lobe is like your personality. So it's very important. It's probably, I would argue, the most important lobe in your brain, because being you is the most important thing ever, right? But for sensation, he just doesn't do a lot. So the occipital lobe, the green one in the back of your head, is for visual, which I know sounds so crazy that, of course, the eyes are in the front of your head, but the occipital lobe interprets vision. So if I look at a picture, it's my eyes, of course, me. looking at the picture, but it's the occipital lobe knows it's a picture of my mom. An occipital lobe remembers everything you've seen. So you don't wake up every day, like seeing everything for the first time. Like, you know, what grass is you've seen grass, the temporal lobe, which is on the side there in yellow. This is for hearing and smell. So the hearing makes sense because your ears are right there, but smell at first doesn't make sense. But then if you think. The temporal lobe kind of hangs above the nasal cavity, which we're about to see when we get into smell in this chapter, especially in the anatomy and lab. And so it's like the olfactory nerve, if you remember from AMP1, if you don't, we're going to see it again, is like laying pretty much on the brain. So it's like, why, this would be like, why would I use a cell phone to call my mom if we're in the same room? So it's just like the nerve impulse is so close to the temporal lobe already, we don't really need to send it to that postcentral gyrus. And then the parietal, which is the purple, is for taste, which seems real squirrely. Because you're tasting, of course, with your tongue. But what the parietal lobe, again, is doing is deciding, do you like that taste? Is that something you've had before? Should you keep eating it? Like, it's the one that's, like, interpreting the taste. The sensory cortex, which is that little strip in the brain, sends a sensation, basically sends a nerve impulse back to the region of stimulation. So we can pinpoint exactly where the sensation is coming from. So the brain gets a signal. it sends a signal back just to verify. So again, I think of this like a cell phone. If you call 911, if I call 911, they're going to verify my address because they don't want to send in the cavalry to the wrong place. So if I'm touching a hot stove, I don't want to jerk. If I'm touching a hot stove with my right hand, I don't want to jerk my left hand away. Like I want to make sure I know where that sensation is specifically coming from. One of the most important things about sensory information is you adapt to it very, very quickly. So this is something that you know, you just maybe don't know that you know that you know. So this is something that you experience, we just maybe didn't have words for it. So sensory receptors adjust to continuous stimulation so that impulses are triggered at slower rates. So that sounds real fancy, okay? But it's basically your brain is getting bombarded by billions and billions and billions of feedback from nerves every single second of every single day. It's almost like email. Sometimes you get so much email, right? Well, I don't need to get an email from my husband to say I'm at work. I'm at work. I'm at work. Like I don't need him to email me every minute of every day to tell me he's at work. I would like an email if he's going away for a work trip, like because that's something different, right? We don't need to be informed if there's no change. So when you walk into a room and your brain gets information about temperature, so your nerves might be firing and saying, it's hot, it's hot, it's hot. Well, your brain doesn't need to hear that. It's hot, it's hot, it's hot, it's hot, it's hot. So if you're in a room that the temperature's not changing, eventually those receptors will fire at less rates. So instead of going, it's hot, it's hot, it's hot, they'll go, it's hot. It's hot. It's hot. Like they'll keep the brain informed, but you can see where the brain just doesn't need to be bombarded with that much information. Just like I don't need a thousand emails from Brent saying he's still at work. So we filter this out because the brain doesn't need to be aware. of this. So you get used to things, right? Well, it's because your brain stops kind of listening to the nerves unless there's something new. So this is how people can like live next to a pig farm. Like I have cousins that have a pig farm and you go over there and it smells so freaking bad. It's just like, I don't know how they do it. Well, they don't smell it anymore because initially their olfactory nerves were saying, smell pig, smell pig, smell pig. Now it's like smell pig. And then maybe like... four hours, smell the pig. Like, and the brain ignores it because there's no change. But maybe that first really hot summer day, they smell their pig farm again. Because now the sensory has gotten like a lot more powerful. So their brain's aware of it. Air fresheners. How many times you put a new air freshener in your car and you're like gagging on pine salt smell. And then like a week later, you can't even smell it. But yet your friends will get in the car and they're like, oh, your car smells good. And you're like, really? Because you don't smell it anymore. Because initially your brain was like pine tree, pine tree, pine tree, pine tree. And now it's like pine tree, pine tree. Like the nerves aren't firing as much and the brain's kind of ignoring it. Now if you changed the scent, if all of a sudden you went for some Yankee Candle goodness, now your brain would like wake up and be like, oh my God, okay, yeah. I smell apples now. Clothing. If you close your eyes right now, you really can't feel your clothes. But like when you first put on a pair of pants, or when you first put on like a class ring or something that's touching your skin. Like I used to be real weird about rings. Like I hated wearing rings. Well, when I got married, I wanted to wear a ring and it drove me crazy for a while. Now I can't even feel the ring. But if I take the ring off, it's like... I'm freaking out because I'm like, I can feel the ring almost tickling. It's because those nerves are waking back up and saying, oh my God, the ring's missing. So you feel this sensation. Background noises. How many times have you been somewhere that had a really annoying background noise? And then eventually you didn't hear it anymore. Like I remember when I was a kid, my grandmother wanted one of those grandfather clocks that like chimed, like bong, bong. And I remember the first night when it went bong. bong, like 12 times at midnight. And I just laid there and counted like one, two, kill me, kill me. And I thought I'm never going to be able to sleep again. And I was actually plotting ways to destroy this clock. I was plotting its death. But after a few nights, I didn't hear it. I grew up on the wrong side of the tracks, as they say. And I mean, we were right by train tracks. And so at night, my bedroom, I was right by the train tracks. And when trains connect, it's like this Like this horrible crashing noise. And I didn't hear it, but I would have friends over for slumber parties and they would be like, oh my God, what the hell was that? And like, they'd freak out. And I'm like, I don't even know what you're hearing. Because again, my brain realized that was part of my environment. And so it kind of ignores it. Another example that's kind of mean, but parents, like how many times, I don't have children. I don't like children. I'll admit it. How many times are you at a restaurant and like a little kid's going, mom, mom, mom, mom, mom, mom, mom. And like, mom is. Totally ignoring the kid and she's talking to her mom or talking to her husband, whatever. And it's like, I'm just sitting there going, can you answer her? Can you answer her? Can you answer her? Cause she's driving me crazy. But I know that mom doesn't hear that kid because if you're a mother, you know how many times a day. you're going to hear mom like 10,000 times a day. To this day, I'm 44, soon to be 45 years old at this point. And if I'm somewhere with my mom, like at Target, I'll be like, mom, and she doesn't hear me. And I'll go, Lee. And like, She's instantly with me. I'm like, you're filtering me out. You think I am unimportant stimuli. So of course kids are important, but I think you moms know that it's not important for you to pay attention to them 24-7, especially when they just want to do a cartwheel for the 30,000th time. So your brain kind of protects itself from being overloaded with the mom, mom, mom, mom, mom. But have you ever noticed then the kid, after it said mom, mom, mom, it'll go mom, and as soon as there's that like, pain in the voice or anger or scared sound to the voice. Like, mom, parents are on it. It's like instantly your brain goes, oh my God, because now the sensation has changed. And so that's the thing with adaptation. If you look at the note at the bottom of this slide, after adaptation, impulses are only triggered again if you increase the stimulus, the strength of the stimulus. So I put in a new air freshener. It could be the same scent, but I would smell it because it was like stronger or the pig farm on a hot summer day. Or if you change the stimulus. So if I change sense, if I put on a sweater, I might feel that sweater. So otherwise, we adapt. So these somatic senses, these body senses that are coming from everywhere, these general senses coming from the receptors in your skin, your muscles, your joints, your organs, like I said. kind of superficial. We can classify these based on the origin of the stimulus. So exteroceptive, these sound terrible, but if we break down the vocab, exteroceptive, this is external. So this is truly superficial. So this is changes to the surface, pressure, touch, temperature, pain. Those are the big four. So pressure and touch differ because if a mosquito is walking on me, that's touch. But like if somebody grabs my arm, that's pressure. Proprioception. Proprioception is knowing where you are in space. So again, closing your eyes, gravity, you respond to gravity. Your joints, your bones, your muscles respond to gravity. And then visceroceptive. I'm sorry, that's my bird. That's Poe. He hears me talking, so he thinks he has to talk. So visceroceptive is changes in the organs themselves, in your viscera, in your ooey-gooey squishy parts. So the touch and pressure receptors are sensitive to these mechanical changes that are displacing, so they're like smooshing or deforming, potentially hurting your tissues. So we have three examples of this. So we did this in AMP1, but it's been a while. You have just free nerve endings. So if you look at this picture, it's basically just a little neuron, right? See all the little dendrites that are going up between those squamous cells that look like the little squashed eggs? So these, there's no synapse. They're not connecting. to anything else. And so it's just basically staying regionally. This is what gives you the sensation of itching. So you ever notice that when you itch, you start scratching and it itches more? That's because if you look at this picture, the more you scratch, those cells will swell because they get irritated and then they push on those little dendrites. So these are just free little nerve endings that let you know a mosquito is walking on you, let you know someone's grabbing you. Just basically neurons. Then we have Meissner's corpuscles and Pachinian corpuscles. So Meissner's corpuscles are for tactile, which you don't really need to know that word, but tactile just means light touch. So these guys are for light touch. Pachinian are for heavy touch. So the way that I remember that is Pachinian starts with P and pressure starts with P. So Meissner's are for light touch. Pachinian. for deep touch pressure. So these are both, we'll see a picture of them next. They're both small, little oval. They look like little buttons that just get pushed. So it makes sense you would have a lot of these in places that you don't have hair. Because if you remember from AMP1, that giant picture of a hair follicle, that around each hair follicle is a tiny little nerve. And so if you take your hand and brush your arm, but don't touch the skin, just touch the hairs. When you bend the hairs, you can feel it, right? Because it's triggering that nerve impulse around the hair follicle. This is why sometimes I'll get home after a long day and I'll take my hair down and my hair hurts. And I'll tell Brent my hair hurts and he's like, your hair doesn't hurt. I'm like, yeah, it does. So ladies, you can relate to this. Or men, if you have really long hair, if you put it in a ponytail, it's like the nerves have been in that one position all day. So then when you like release it, all these nerve impulses fire and it can hurt. Or if you like brush your hair the opposite way that it's used to laying, it feels weird. So all of these hair follicles have this nerve ending. And so it makes sense that you would have tons of Meissner's corpuscles where you don't have hair because you're not getting the benefit of all those nerve endings. So this is places like your lips, your fingertips, the palms and soles of your feet. You can't have hair on the palms and soles of your feet. You wouldn't be able to grab stuff. Your nipples, good times, and external genitals, which is the last unit. So this is like... penis and vagina territory, man. AMP2 gets good with reproductive anatomy. So all of those things don't have hair, but they are still very sensitive parts of your body. And obviously for the things that we expect these guys to do, we need them to be sensitive. Pacheny and corpuscles are lamellated. You do not need to know the word lamellated, but you're going to see it a lot. It basically just means ringed. So we'll see on the picture that it looks like little tree rings. So I'm never going to ask you what lamella means. But you'll just see that word come up in lab a lot to help you find structures that look like tree rings. So these guys, again, look a lot like Meissner's corpuscles. They look like little buttons to get pushed. So we have heavy touch. We have deep pressure, vibrations. These are located in that hypodermis, in the subcutaneous tissue, in your hands, your feet, your genitals, your breasts, your tendons, ligaments. So that way, again, your body is getting information that potentially that deep pressure could cause damage. You could get to where you're breaking bones or bruising the skin. So it's very important to be able to tell the difference between light touch and deep touch. But let's look at the picture. These three layers should be familiar. We did them last semester. So we have epidermis, the top layer, the dermis, the middle layer, and then the hypodermis or subcutaneous layer. So if we think about logic here, we can't have any receptors in the epidermis. Because remember, the epi, epi means on, on the dermis, the epidermis is the top layer that falls off basically every day. So if you burn yourself or scratch yourself, it heals usually because that layer is just sloughing off every single day. So we can't have any receptors there because then the receptors would slough off. And so then we wouldn't be able to feel pain or we wouldn't be able to feel temperature and then we would be in some trouble. So the epidermis, because of its job, which is to protect you by falling off every day, it doesn't have any sensation. So most of your sensory information is in the dermis. And this makes sense, right? Because you wouldn't want temperature receptors or pain receptors in the hypodermis because it would almost be too late. Because the dermis is where your blood is. And so it's like, if you don't feel pain in that layer, you would cut yourself really, really deeply before you were even aware of it. So it makes sense that almost all the receptors are in the dermis. So we can see the thermoreceptors there, the Meissner's corpuscles. If you look at those, those guys are for light touch. So see how that Meissner's corpuscle which kind of looks like sperm, which we have sperm anatomy this semester. It's thrilling. How it's touching the epidermis, but it's not in the epidermis. So it's like that, that Meissner's corpuscle is as high up as you can get feeling, which makes sense if it's trying to feel light touch. It has to be as high up as it can be. The nociceptors, basically just little dendrites, are experiencing pain. So again, we don't want to experience pain in the third layer. I mean, we do, but we don't want to experience it for the first time. the third layer because we would really hurt ourselves. So the only sensory receptor that's in the hypodermis is the pachinion. And so again, pachinion, pressure. They both start with P. I need to know the difference if you compare this picture between the Meissner's corpuscle and the pachinion. I need to know the difference between light touch and deep touch. So their location makes perfect sense. Thermoreceptors, easy to remember because you use a thermometer to take your temperature, right? So these are free nerve endings. They're just those little dangly dendrites that respond to both heat and cold. So they kind of look like just little buttons that are getting pushed here. So you don't have to know these numbers. I never ask numbers. If I do, I always specifically say you need to know numbers. Otherwise, if I give you numbers, they're just for reference. So heat receptors trigger. They're the most sensitive between 77 and 113. So I know how some of you are because you like the heat. I hate to be hot. I'm so whiny. I hate summer. I hate heat. So 77 is too hot for me. Some of you are like, oh my God, 77 is awesome. It's just getting good. So everybody's different, right? So heat receptors just become sensitive at 77. Even though you may not think that's that hot, that's just when these guys are activated. And then 113. 113 is hot. So my best friend moved to Phoenix. and left me. And I went out there to visit her and I wanted to die. Like I cannot handle that heat. That's crazy. So it was like 112 degrees when I was there. It was nuts. So above that, the pain receptors kick in because human tissue gets very, very damaged after that. And so you want to, your body needs to know, okay, it is not safe to be in this level of temperature. The cold receptor is sensitive at 50. I don't think 50 is cold. 50 to 68 is not cold to me. In fact, that's like my happy temperature range. That's like where I want to be is between 50 and 68. But you can see where this is getting to the point where we need these receptors to say, hey, the body is starting to cool down or the environment is starting to cool down because if we hit 32, we're going to freeze to death. So below 50, we want the pain receptors to kick in. Like pain sucks. Burning, freezing sucks. Pain sucks. But we need pain to tell us to get the hell out of that situation. But thermoreceptors do adapt pretty quickly. Like I don't know about you, but in the morning when I crank on my shower, I turn it all the way up to where like the steam is like billowing out of the shower. Then I get into the shower and I'm like, oh my God, it's hot. And then I turn it down. And then about two minutes later, I turn it right back up to where it was when I thought it was really hot. Because I got used to it. Or I'm lucky enough to have a hot tub, which is one of my greatest treasures, honestly. And, um, I get in my hot tub and it's like, at first I'll step into it. I'm like, Oh my God, this is so hot. Which Brent's like, it's a hot tub. I'm like, you're funny. But yeah, I get it. So you get in this 102 degree hot tub and it's like, Oh my God, it's so unbearably hot. And then you sit in it for like five minutes and it's like, this is perfect. Cause you get used to it. Swimming on a cold, on the first like cold spring day that everybody wants to get into their swimming pool. You first get in, it is so cold that you think you're going to die. But then after about 10 minutes, you're swimming around like, this is great. The lab, I know, can sometimes, the lab room can sometimes be cold. So the point is you get used to it. Like you first walk into an air-conditioned room, you're like, oh my God, this feels so good. And then sometimes five minutes later, it doesn't even feel cold anymore because you've adapted. Now, you will never adapt to below 32 degrees. You will never adapt to above 212 degrees. So no matter if I put you in that hot tub and I raise it one degree an hour, you're never going to get used to boiling, right? So there are still the extremes that we can't handle, but we can adapt to temperature reasonably well.

And so this is going to have some of that. But don't worry if it's been a while since you had A&P 1. Anything that you need from A&P 1, I will completely review. So hopefully you'll remember it. But if you don't, you'll just have to.

learn it again, no problem. So don't think you're behind. Nobody's behind. Okay, so the whole goal of senses is to link the external environment, so the outside world, to what's happening inside. So it all goes back to homeostasis.

So if you didn't learn anything in A&P 1, hopefully you learned homeostasis, because that is the... number one idea of physiology. This is the underlying idea of physiology. So if you don't remember homeostasis, the reason I have this little picture here is homeostasis is maintaining balance. So it's basically maintaining control of the inside of your body.

So the outside world is so crazy chaotic, especially right now, but your inside is very calm. So homeostasis is basically just maintaining that. balance. And so keeping your temperature balanced, even though it could be 80 degrees outside or negative 20 degrees outside, your body temperature is still around 98.6. So maintaining your breathing, your heart rate, your pH levels.

So maintaining a constant internal environment is the nerdy definition of homeostasis. Maintaining a constant internal environment. So this chapter is about senses. So how can I control what's going on inside my body if I don't know what the heck's going on out there?

So I have to make sure that I'm connected, that I know what the temperature is. How would I know if I'm supposed to sweat or shiver if I don't know what the outside temperature is? So there are different types of senses. So we have general senses that are located all over your body.

So general, if you think of the word general, these are generally located all over your body. They're very, very simple. They're almost like little buttons that get pushed. So you have touch, pressure, vibration, pain, temperature, proprioception, which I do define on a slide coming up. I don't know why I don't put it on this one.

So proprioception is knowing where you are in space. So like if you close your eyes and put your arms out to your sides. Like you know your arms are out to the side.

I'm sitting in a chair right now. I know my feet are pointing down. Fluid pressure. So this can be in your ear, which affects balance.

But also blood pressure. Like I know when I'm pissed off, right? Like I can feel that blood pressure surge.

Then we have somatic. And so these general senses, whether you're talking touch pressure, vibration, temperature, whatever. These can be felt from two different places.

Somatic versus visceral. So somatic means body. but that's not very helpful in anatomy school because everything is body, right?

But somatic is body. What I think of with somatic is I think more of the surface of the body, more superficial things like your skin and your muscles, your tendons and your joints. So these are things that are kind of on the periphery of your body. So like the torso would be more the central part of your body, right?

These are things that are giving you peripheral information. Like when you touch a hot stove, that's going to come somatically. versus visceral.

If you remember the word viscera, viscera means organs. I call them ooey gooey squishy parts. And so viscera being the ooey gooey squishy parts, I need to know when my stomach is full.

I need to know when my bladder is full and it's time to pee. You need to know when it's time to duty. You need to know when your heart's racing. So you need information from the organs themselves.

So touch, pressure, vibration, pain, temperature, proprioception, fluid pressure, generally all over your body. But we talk about them more on the surface, somatically. Or we talk about them deep inside, visceral. Because it's a very different sensation, a mosquito walking on your skin, versus your stomach stretching because you just had a cheeseburger.

God, a cheeseburger sounds good. So in A&P 1, we talked about general senses a little bit when we did the integumentary system, when we did the skin, because the skin has touch receptors and temperature receptors and everything else. But this semester, we more focus on special senses.

And that's what our first two labs will be is special senses. So this is olfaction, which is smell. Gustation, which I think is a fun word, especially if you say gustation, is taste. So I always think that like gustate, like has taste kind of in the word, gustation.

Sounds like taste almost, because otherwise that's a weird word. Vision, which is, of course, seeing things. And then your ear is in charge of both, of course, hearing and equilibrium.

Equilibrium is balance. So instead of being all over the body, like the general senses, these are in very specific regions of the head. So your head does a lot of things, right? It's not like you can see with your toes or see with your elbows or smell or taste with your fingers.

which would make restaurants weird. Okay. Imagine if you tasted with your toes. I mean, restaurants would be a whole different game.

So these are things that are in the head and they're very complex. As we're going to see in lab. I mean, it is complicated to see. The eyeball is complicated, which shouldn't it be? I mean, seeing is complicated.

Hearing is complicated. So anatomically, these guys are a bit of a nightmare. Okay, so to review, it's all about sending information to the brain and away from the brain.

So these are like nerve superhighways. You touch the hot stove. You need that information to travel down your arm, up to your brain. Your brain decides, okay, how hot is it? Should I do something about it?

And then the brain sends a signal to the muscles, so we now go back down to the arm, out to the hand, to jerk the hand away if it's hot, or leave the hand there if it's nice and warm and you like it. So it's just like kind of like Interstate 74 has the east and west lanes. We've got a two-way street here. So if you don't remember these terms, you may want to write them down. Corticospinal tract and spinothalamic tracts.

These are like the east and west lanes of 74. These are the nerve pathways. These are the nerve superhighways that are going up your spinal cord to the brain and then bring back down the spinal cord and then out to the nerves. So corticospinal tract. Cortex, if you remember that word. If you don't.

It's fine, but we're going to use it a lot this semester. Cortex is the surface of an organ. So this is the surface of your brain. So if you're going from the cortex to the spine, you're going down, obviously, right?

You're going from the brain to the spinal cord. So information is going out. So we would call that efferent with an E. And the way that I remember that is I think E for exit.

So this is the brain has made a decision and it's sending its response. So it's efferent. Another word we had from last semester is this would be a motor response because motor is movement so that's what the brain is doing it's causing movement. So corticospinal tract is going from the cortex the surface of the brain down your spine so it's leaving the brain So it's efferent, and it's a movement, so it's motor. The other one is bringing information to the brain.

So this is going up the spine to the brain, and if you remember, there's that structure in the middle of the brain that's called the thalamus. So this is the spinothalamic tract. So it's going from the spine to the thalamus. That's obviously bringing information to the brain. So this is afferent with an A, just means to the brain or to the nervous system.

And this is a sensation. So this is a sensory pathway. So these are your two pathways.

You're either sensing things or you're motoring. You're either sensing or you're moving to respond to that sensation. So these are the two major tracks.

So the function of all these receptors you have all over your body is to turn whatever stimulus it is, whether it's touch, temperature, pain, smell, pressure, whatever, into an action potential. So we did that in AMP1, and boy was that not just the best time of your life, okay? The nervous system, it rocks everybody's world with the whole acetylcholine opening the doors, the sodium can rush in, and you had to go from negative 70 to negative 60 millivolts, and it was crazy.

So we've already done that. So I'm assuming you already know how nerves fire. You may not remember the details, but you've already took tests on that.

So for this semester, we're basically just saying an action potential, which we had in AMP1, now we're just basically thinking, okay, the nerve's firing. So we need enough stimulus to cause threshold to be achieved. If you remember from AMP1, that meant we had to have enough doors open to let enough sodium in to get us from negative 70 to negative 60. We called that threshold. Again, though, for this semester, just think the nerve has to fire.

You have to get enough. like stimulus to cause the nerves to fire. Some of the receptors in your body aren't very fancy. So they're just like little neurons.

So I have this little picture of the neuron up there, if you don't remember the parts of the neurons. We have the little dendrites, so those are on the right side. The little dangly dendrites is how I always remember them. Dangly dendrites.

So you have several of those. And then on the left, you have that one long axon. So most of the time, 99% of the time, the neurons have one axon. But there are exceptions that we're about to see. But a lot of these receptors, like I said, that are more like touch receptors, that are more like little buttons that get pushed, they kind of look like these little neurons.

So they respond to the stimulus. The dendrites gather the information, and they send it away on the axon. So that's how I remember it, A and away, axon, away.

So the whole point of a stimulus, whether it's temperature or pain, is to let us know there's a change in the environment. Because homeostasis tells me I have to maintain an internal happy place. I have to maintain this internal balance.

Well, how can I do that if I can't react to the outside world? We always use temperature because it's so easy. But think about how many different temperatures you're exposed to on a daily basis.

When it's summer and it's so hot outside you want to die, you walk inside and the air conditioning is sometimes so cold you need a sweater. Well, again, if I didn't know about that change, how would I know if I'm supposed to put on that sweater? How am I supposed to know if I'm supposed to sweat or shiver?

So when the environment changes, that's when we got to know what's going on because we need to make a change. So this happens because those dendrites and the cell body, which is where the nucleus is, are going to get graded potentials. And if you don't remember that from AMP1, again, I'm not testing you over this again because we already did it.

But that just meant that different parts of the neuron can be experiencing different stimulation. Kind of like a room. If you have a room with an air conditioner, if you're close to the window unit air conditioner, you're going to be really, really cold.

If you're on the other side of the room, you might not even feel it. So if you think of that neuron, if one of the dendrites is picking up a stimulus, the other dendrites might not be affected at all. And so we call this a graded potential.

We just need enough sodium to rush in. to cause us to get to threshold. We got to get, if you remember the axon hillock, which is like the little neck of the axon or right before the axon starts, it's like the neck of the neuron. We had to be at negative 60. So our whole goal though is to initiate these nerve impulses, afferent. So we're bringing things to the brain and spinal cord.

That's the whole goal of sensation, right? What does it matter if you can touch a hot stove if you can't tell your brain it's hot? Like that's not going to work out.

So we have to be able to send smell to our brain. We have to be able to send taste, temperature, pressure, all this information to our brain so our brain could decide what to do about it. So CNS is just central nervous system.

We classify sensory receptors based on the stimulus that they respond to. So you do need to know these terms. So mechanoreceptors are responding to mechanical changes. So touch, if you touch something, it changes your tissue mechanically. pressure the fancy term for a pressure receptor is a baroreceptor so I always think barometers like for weather always talk about pressure changes with weather like the barometric pressure is doing this whatever vibration stretch body position which again that nerdy word is proprioception so on that previous slide I said I didn't define it this is when you close your eyes and stick your arms out you know where you are and hearing so all of these are mechanical changes to your body like the tissue is physically changing.

Thermoreceptors, that one's easy. That's temperature. Photoreceptor, that one's easy. If you think photography, you need light, like nothing blinds you more than an iPhone camera, right? Chemoreceptors, chemo being chemicals.

And when you hear chemicals, everybody gets all bent out of shape, like, oh my God, chemicals are so evil. But your whole body's chemicals. And this is why we can smell. So this is why olfaction happens and why we can taste, which taste is one of the best things ever, right?

All because these chemicals dissolve. And then nociceptors are pain receptors. So the way that I remember this is I think nociceptors, I think Novocaine for pain, even though that really doesn't make sense, but that's just the stupid way I remember it.

So pain can come from tissue damage. So you cut yourself or your dog bit you. Extreme temperature. Like, oh, don't we love Illinois?

You go outside when it's so hot and you feel like your skin's frying, but then you also go out in those negative 25 wind chills where your nose hairs stick together. And that hurts just as much. Frostbite does not look like a good time.

And then, of course, chemical damage. Like if you spilled phenol, the cadaver chemical, on you and left it on there too long. Or acid. Or bleach. So pain sucks, but it's very important for our body to know what's going on so we can make changes.

Where does this information go? So once we go up that spinophthalmic tract, the part of your brain that receives this information is the postcentral gyrus, which if you don't remember that, we're gonna see it in lab. Again, we had this in AMP1. Those were those two strips on the brain.

So the one that's highlighted there is the postcentral gyrus. The one in front of it is the precentral gyrus. And so if you look at this diagram, it says somatosensory cortex.

That sounds hella fancy, but cortex just means surface. sensory is the information you're bringing in and somato remember just means body so this basically just means the surface of the brain getting all of the body's sensory information so i think of this like a cell phone tower when i call my mom it doesn't just go to her it goes to a cell phone tower and then to her so when you when you um sorry smell is different so smells the weird exception to this but every other sensation okay say i touch um a cold ice cube you That information is going to travel down my arm. It's going to go up the spinothalamic tract, and it's going to stop at this strip in the brain. And then that is going to be sent, from there on, it'll be sent to the region of the brain that deals with temperature. So it's just a stopping point for all the sensory information, except for smell, because smell is really strange.

So once information has gone to that strip, the brain then sends it on to wherever deals with it. Just like that cell phone tower sends the signal to my mom's phone. So if you look at this little picture of the brain, we had this last semester, we had the lobes of the brain.

So the frontal lobe is that kind of pinkish-orange color. It's the largest lobe of the brain. Now, this is not an important lobe for this chapter because your frontal lobe is why you have the personality you have. It's why I have my dazzling sense of humor.

my sarcasm, my love of travel and pizza rolls. So your frontal lobe is like your personality. So it's very important. It's probably, I would argue, the most important lobe in your brain, because being you is the most important thing ever, right? But for sensation, he just doesn't do a lot.

So the occipital lobe, the green one in the back of your head, is for visual, which I know sounds so crazy that, of course, the eyes are in the front of your head, but the occipital lobe interprets vision. So if I look at a picture, it's my eyes, of course, me. looking at the picture, but it's the occipital lobe knows it's a picture of my mom. An occipital lobe remembers everything you've seen.

So you don't wake up every day, like seeing everything for the first time. Like, you know, what grass is you've seen grass, the temporal lobe, which is on the side there in yellow. This is for hearing and smell. So the hearing makes sense because your ears are right there, but smell at first doesn't make sense.

But then if you think. The temporal lobe kind of hangs above the nasal cavity, which we're about to see when we get into smell in this chapter, especially in the anatomy and lab. And so it's like the olfactory nerve, if you remember from AMP1, if you don't, we're going to see it again, is like laying pretty much on the brain.

So it's like, why, this would be like, why would I use a cell phone to call my mom if we're in the same room? So it's just like the nerve impulse is so close to the temporal lobe already, we don't really need to send it to that postcentral gyrus. And then the parietal, which is the purple, is for taste, which seems real squirrely. Because you're tasting, of course, with your tongue. But what the parietal lobe, again, is doing is deciding, do you like that taste?

Is that something you've had before? Should you keep eating it? Like, it's the one that's, like, interpreting the taste.

The sensory cortex, which is that little strip in the brain, sends a sensation, basically sends a nerve impulse back to the region of stimulation. So we can pinpoint exactly where the sensation is coming from. So the brain gets a signal.

it sends a signal back just to verify. So again, I think of this like a cell phone. If you call 911, if I call 911, they're going to verify my address because they don't want to send in the cavalry to the wrong place.

So if I'm touching a hot stove, I don't want to jerk. If I'm touching a hot stove with my right hand, I don't want to jerk my left hand away. Like I want to make sure I know where that sensation is specifically coming from.

One of the most important things about sensory information is you adapt to it very, very quickly. So this is something that you know, you just maybe don't know that you know that you know. So this is something that you experience, we just maybe didn't have words for it. So sensory receptors adjust to continuous stimulation so that impulses are triggered at slower rates.

So that sounds real fancy, okay? But it's basically your brain is getting bombarded by billions and billions and billions of feedback from nerves every single second of every single day. It's almost like email.

Sometimes you get so much email, right? Well, I don't need to get an email from my husband to say I'm at work. I'm at work. I'm at work.

Like I don't need him to email me every minute of every day to tell me he's at work. I would like an email if he's going away for a work trip, like because that's something different, right? We don't need to be informed if there's no change.

So when you walk into a room and your brain gets information about temperature, so your nerves might be firing and saying, it's hot, it's hot, it's hot. Well, your brain doesn't need to hear that. It's hot, it's hot, it's hot, it's hot, it's hot. So if you're in a room that the temperature's not changing, eventually those receptors will fire at less rates. So instead of going, it's hot, it's hot, it's hot, they'll go, it's hot.

It's hot. It's hot. Like they'll keep the brain informed, but you can see where the brain just doesn't need to be bombarded with that much information. Just like I don't need a thousand emails from Brent saying he's still at work.

So we filter this out because the brain doesn't need to be aware. of this. So you get used to things, right? Well, it's because your brain stops kind of listening to the nerves unless there's something new.

So this is how people can like live next to a pig farm. Like I have cousins that have a pig farm and you go over there and it smells so freaking bad. It's just like, I don't know how they do it.

Well, they don't smell it anymore because initially their olfactory nerves were saying, smell pig, smell pig, smell pig. Now it's like smell pig. And then maybe like... four hours, smell the pig. Like, and the brain ignores it because there's no change.

But maybe that first really hot summer day, they smell their pig farm again. Because now the sensory has gotten like a lot more powerful. So their brain's aware of it. Air fresheners.

How many times you put a new air freshener in your car and you're like gagging on pine salt smell. And then like a week later, you can't even smell it. But yet your friends will get in the car and they're like, oh, your car smells good. And you're like, really?

Because you don't smell it anymore. Because initially your brain was like pine tree, pine tree, pine tree, pine tree. And now it's like pine tree, pine tree.

Like the nerves aren't firing as much and the brain's kind of ignoring it. Now if you changed the scent, if all of a sudden you went for some Yankee Candle goodness, now your brain would like wake up and be like, oh my God, okay, yeah. I smell apples now.

Clothing. If you close your eyes right now, you really can't feel your clothes. But like when you first put on a pair of pants, or when you first put on like a class ring or something that's touching your skin. Like I used to be real weird about rings.

Like I hated wearing rings. Well, when I got married, I wanted to wear a ring and it drove me crazy for a while. Now I can't even feel the ring. But if I take the ring off, it's like...

I'm freaking out because I'm like, I can feel the ring almost tickling. It's because those nerves are waking back up and saying, oh my God, the ring's missing. So you feel this sensation. Background noises.

How many times have you been somewhere that had a really annoying background noise? And then eventually you didn't hear it anymore. Like I remember when I was a kid, my grandmother wanted one of those grandfather clocks that like chimed, like bong, bong. And I remember the first night when it went bong. bong, like 12 times at midnight.

And I just laid there and counted like one, two, kill me, kill me. And I thought I'm never going to be able to sleep again. And I was actually plotting ways to destroy this clock. I was plotting its death. But after a few nights, I didn't hear it.

I grew up on the wrong side of the tracks, as they say. And I mean, we were right by train tracks. And so at night, my bedroom, I was right by the train tracks.

And when trains connect, it's like this Like this horrible crashing noise. And I didn't hear it, but I would have friends over for slumber parties and they would be like, oh my God, what the hell was that? And like, they'd freak out. And I'm like, I don't even know what you're hearing. Because again, my brain realized that was part of my environment.

And so it kind of ignores it. Another example that's kind of mean, but parents, like how many times, I don't have children. I don't like children. I'll admit it.

How many times are you at a restaurant and like a little kid's going, mom, mom, mom, mom, mom, mom, mom. And like, mom is. Totally ignoring the kid and she's talking to her mom or talking to her husband, whatever. And it's like, I'm just sitting there going, can you answer her? Can you answer her?

Can you answer her? Cause she's driving me crazy. But I know that mom doesn't hear that kid because if you're a mother, you know how many times a day.

you're going to hear mom like 10,000 times a day. To this day, I'm 44, soon to be 45 years old at this point. And if I'm somewhere with my mom, like at Target, I'll be like, mom, and she doesn't hear me. And I'll go, Lee.

And like, She's instantly with me. I'm like, you're filtering me out. You think I am unimportant stimuli. So of course kids are important, but I think you moms know that it's not important for you to pay attention to them 24-7, especially when they just want to do a cartwheel for the 30,000th time. So your brain kind of protects itself from being overloaded with the mom, mom, mom, mom, mom.

But have you ever noticed then the kid, after it said mom, mom, mom, it'll go mom, and as soon as there's that like, pain in the voice or anger or scared sound to the voice. Like, mom, parents are on it. It's like instantly your brain goes, oh my God, because now the sensation has changed.

And so that's the thing with adaptation. If you look at the note at the bottom of this slide, after adaptation, impulses are only triggered again if you increase the stimulus, the strength of the stimulus. So I put in a new air freshener.

It could be the same scent, but I would smell it because it was like stronger or the pig farm on a hot summer day. Or if you change the stimulus. So if I change sense, if I put on a sweater, I might feel that sweater. So otherwise, we adapt.

So these somatic senses, these body senses that are coming from everywhere, these general senses coming from the receptors in your skin, your muscles, your joints, your organs, like I said. kind of superficial. We can classify these based on the origin of the stimulus. So exteroceptive, these sound terrible, but if we break down the vocab, exteroceptive, this is external. So this is truly superficial.

So this is changes to the surface, pressure, touch, temperature, pain. Those are the big four. So pressure and touch differ because if a mosquito is walking on me, that's touch. But like if somebody grabs my arm, that's pressure. Proprioception.

Proprioception is knowing where you are in space. So again, closing your eyes, gravity, you respond to gravity. Your joints, your bones, your muscles respond to gravity.

And then visceroceptive. I'm sorry, that's my bird. That's Poe. He hears me talking, so he thinks he has to talk. So visceroceptive is changes in the organs themselves, in your viscera, in your ooey-gooey squishy parts.

So the touch and pressure receptors are sensitive to these mechanical changes that are displacing, so they're like smooshing or deforming, potentially hurting your tissues. So we have three examples of this. So we did this in AMP1, but it's been a while. You have just free nerve endings.

So if you look at this picture, it's basically just a little neuron, right? See all the little dendrites that are going up between those squamous cells that look like the little squashed eggs? So these, there's no synapse.

They're not connecting. to anything else. And so it's just basically staying regionally. This is what gives you the sensation of itching.

So you ever notice that when you itch, you start scratching and it itches more? That's because if you look at this picture, the more you scratch, those cells will swell because they get irritated and then they push on those little dendrites. So these are just free little nerve endings that let you know a mosquito is walking on you, let you know someone's grabbing you.

Just basically neurons. Then we have Meissner's corpuscles and Pachinian corpuscles. So Meissner's corpuscles are for tactile, which you don't really need to know that word, but tactile just means light touch.

So these guys are for light touch. Pachinian are for heavy touch. So the way that I remember that is Pachinian starts with P and pressure starts with P.

So Meissner's are for light touch. Pachinian. for deep touch pressure.

So these are both, we'll see a picture of them next. They're both small, little oval. They look like little buttons that just get pushed.

So it makes sense you would have a lot of these in places that you don't have hair. Because if you remember from AMP1, that giant picture of a hair follicle, that around each hair follicle is a tiny little nerve. And so if you take your hand and brush your arm, but don't touch the skin, just touch the hairs. When you bend the hairs, you can feel it, right? Because it's triggering that nerve impulse around the hair follicle.

This is why sometimes I'll get home after a long day and I'll take my hair down and my hair hurts. And I'll tell Brent my hair hurts and he's like, your hair doesn't hurt. I'm like, yeah, it does. So ladies, you can relate to this. Or men, if you have really long hair, if you put it in a ponytail, it's like the nerves have been in that one position all day.

So then when you like release it, all these nerve impulses fire and it can hurt. Or if you like brush your hair the opposite way that it's used to laying, it feels weird. So all of these hair follicles have this nerve ending. And so it makes sense that you would have tons of Meissner's corpuscles where you don't have hair because you're not getting the benefit of all those nerve endings.

So this is places like your lips, your fingertips, the palms and soles of your feet. You can't have hair on the palms and soles of your feet. You wouldn't be able to grab stuff. Your nipples, good times, and external genitals, which is the last unit. So this is like...

penis and vagina territory, man. AMP2 gets good with reproductive anatomy. So all of those things don't have hair, but they are still very sensitive parts of your body. And obviously for the things that we expect these guys to do, we need them to be sensitive.

Pacheny and corpuscles are lamellated. You do not need to know the word lamellated, but you're going to see it a lot. It basically just means ringed.

So we'll see on the picture that it looks like little tree rings. So I'm never going to ask you what lamella means. But you'll just see that word come up in lab a lot to help you find structures that look like tree rings.

So these guys, again, look a lot like Meissner's corpuscles. They look like little buttons to get pushed. So we have heavy touch.

We have deep pressure, vibrations. These are located in that hypodermis, in the subcutaneous tissue, in your hands, your feet, your genitals, your breasts, your tendons, ligaments. So that way, again, your body is getting information that potentially that deep pressure could cause damage.

You could get to where you're breaking bones or bruising the skin. So it's very important to be able to tell the difference between light touch and deep touch. But let's look at the picture. These three layers should be familiar. We did them last semester.

So we have epidermis, the top layer, the dermis, the middle layer, and then the hypodermis or subcutaneous layer. So if we think about logic here, we can't have any receptors in the epidermis. Because remember, the epi, epi means on, on the dermis, the epidermis is the top layer that falls off basically every day. So if you burn yourself or scratch yourself, it heals usually because that layer is just sloughing off every single day. So we can't have any receptors there because then the receptors would slough off.

And so then we wouldn't be able to feel pain or we wouldn't be able to feel temperature and then we would be in some trouble. So the epidermis, because of its job, which is to protect you by falling off every day, it doesn't have any sensation. So most of your sensory information is in the dermis.

And this makes sense, right? Because you wouldn't want temperature receptors or pain receptors in the hypodermis because it would almost be too late. Because the dermis is where your blood is.

And so it's like, if you don't feel pain in that layer, you would cut yourself really, really deeply before you were even aware of it. So it makes sense that almost all the receptors are in the dermis. So we can see the thermoreceptors there, the Meissner's corpuscles.

If you look at those, those guys are for light touch. So see how that Meissner's corpuscle which kind of looks like sperm, which we have sperm anatomy this semester. It's thrilling. How it's touching the epidermis, but it's not in the epidermis. So it's like that, that Meissner's corpuscle is as high up as you can get feeling, which makes sense if it's trying to feel light touch.

It has to be as high up as it can be. The nociceptors, basically just little dendrites, are experiencing pain. So again, we don't want to experience pain in the third layer. I mean, we do, but we don't want to experience it for the first time.

the third layer because we would really hurt ourselves. So the only sensory receptor that's in the hypodermis is the pachinion. And so again, pachinion, pressure. They both start with P. I need to know the difference if you compare this picture between the Meissner's corpuscle and the pachinion.

I need to know the difference between light touch and deep touch. So their location makes perfect sense. Thermoreceptors, easy to remember because you use a thermometer to take your temperature, right?

So these are free nerve endings. They're just those little dangly dendrites that respond to both heat and cold. So they kind of look like just little buttons that are getting pushed here. So you don't have to know these numbers.

I never ask numbers. If I do, I always specifically say you need to know numbers. Otherwise, if I give you numbers, they're just for reference. So heat receptors trigger. They're the most sensitive between 77 and 113. So I know how some of you are because you like the heat.

I hate to be hot. I'm so whiny. I hate summer.

I hate heat. So 77 is too hot for me. Some of you are like, oh my God, 77 is awesome. It's just getting good. So everybody's different, right?

So heat receptors just become sensitive at 77. Even though you may not think that's that hot, that's just when these guys are activated. And then 113. 113 is hot. So my best friend moved to Phoenix.

and left me. And I went out there to visit her and I wanted to die. Like I cannot handle that heat. That's crazy. So it was like 112 degrees when I was there.

It was nuts. So above that, the pain receptors kick in because human tissue gets very, very damaged after that. And so you want to, your body needs to know, okay, it is not safe to be in this level of temperature. The cold receptor is sensitive at 50. I don't think 50 is cold.

50 to 68 is not cold to me. In fact, that's like my happy temperature range. That's like where I want to be is between 50 and 68. But you can see where this is getting to the point where we need these receptors to say, hey, the body is starting to cool down or the environment is starting to cool down because if we hit 32, we're going to freeze to death. So below 50, we want the pain receptors to kick in.

Like pain sucks. Burning, freezing sucks. Pain sucks. But we need pain to tell us to get the hell out of that situation.

But thermoreceptors do adapt pretty quickly. Like I don't know about you, but in the morning when I crank on my shower, I turn it all the way up to where like the steam is like billowing out of the shower. Then I get into the shower and I'm like, oh my God, it's hot.

And then I turn it down. And then about two minutes later, I turn it right back up to where it was when I thought it was really hot. Because I got used to it.

Or I'm lucky enough to have a hot tub, which is one of my greatest treasures, honestly. And, um, I get in my hot tub and it's like, at first I'll step into it. I'm like, Oh my God, this is so hot. Which Brent's like, it's a hot tub.

I'm like, you're funny. But yeah, I get it. So you get in this 102 degree hot tub and it's like, Oh my God, it's so unbearably hot.

And then you sit in it for like five minutes and it's like, this is perfect. Cause you get used to it. Swimming on a cold, on the first like cold spring day that everybody wants to get into their swimming pool. You first get in, it is so cold that you think you're going to die. But then after about 10 minutes, you're swimming around like, this is great.

The lab, I know, can sometimes, the lab room can sometimes be cold. So the point is you get used to it. Like you first walk into an air-conditioned room, you're like, oh my God, this feels so good. And then sometimes five minutes later, it doesn't even feel cold anymore because you've adapted. Now, you will never adapt to below 32 degrees.

You will never adapt to above 212 degrees. So no matter if I put you in that hot tub and I raise it one degree an hour, you're never going to get used to boiling, right? So there are still the extremes that we can't handle, but we can adapt to temperature reasonably well.

Transcript for:Understanding the Human Senses

Transcript for:
Understanding the Human Senses