Sensory Processing, Vestibular System, and Eye Anatomy MCAT Review

[Music] Hello and welcome to the first growth series, MCAT Content Review Podcast with actual content in it. All right, so this is the first episode where I'm actually going to be talking about psychology. It'll be really fun. So I'm going to start off with how the AAMC C psychology in the MCAT, and then we're going to get into the actual content. So let's just jump right into it. So I'm going to be splitting these different concepts into different ways, all right. So with psychology, the AAMC has designed five foundational concepts. Those are concepts six through ten, all right. I personally found that the order concepts are pretty unorganized, but generally I think concept six and seven have to do with the like physiology of psychology. While concepts eight, nine, and ten are like the nitty gritty, you know, the theories, this concepts, sociology, etc. So I'm going to start with foundational concepts six, not because it makes sense to go in order to learn properly, but I mean, I don't want to jump around, confuse you guys. I'll just go in order six through ten. So we'll get right into it. If you feel like I'm talking too fast or too slow, you can always adjust the podcast speed. But yeah, here goes the content part. So in foundational concepts six, the AAMC wants to know a few broad topics. Those are sensing the environment, making sense of the environment and responding to the world. So that kind of, you know, has to do with senses, all that stuff, you know, we're dealing with your eyes, your ears, cognition, etc. So in this episode, I will go over sensory processing and the physiological aspects of vision. So sensory processing, all right. So we know a vision has four cues. I call those form DMC. It's kind of like run DMC. So funny. All right. So form DMC, it's form, depth, motion, and constancy, form DMC. All right. So first in that form DMC model is form pretty simple, you know, just to save an object, not that bad. So we really only need one eye to identify form and using only one eye that's called monocular cues. So you can see size and height, just, you know, judging on other objects around it. And you can also see the overlapping of an object on another and the shading and contour by using lights and shadows. So basically for form, just no form has to do with monocular vision. And it can be used with, you know, size, height, overlap, shading, all that stuff. Form is just like the state of an object. All right. So form DMC, we checked off the form part. We'll get to the D part. That is depth. So what allows us to perceive depth? That's having two eyes. So having two eyes is binocular cues. And you need to know two things about having two eyes. So first, having our eyes separated is amazing. Having that slightly different view of an object is what gives us depth. All right. And the second thing you got to know about those binocular cues having two eyes is convergence. So let's stare at your nose for like 10 seconds. All right. That was in 10 seconds, but I know half you guys aren't doing it. So you know, who cares? Well, if you did do it, did you notice your eyes kind of get a little strained? Well, that's because when we look at things that are close to us, our eye muscles contract. So your nose is super close to your eyes. Your eye muscles are really contracting. It gets super strained. Now, if we look at things far away from us, our eyes get relaxed. So conversions, you know, looking close in a way, that has to do with depth. So basically for depth, just no depth means binocular vision, which means two eyes. And we can see binocular vision with retinal disparity, which is when our retinas, our eyes are on, you know, different places and conversions. So form is done. Depth is done. So we have the MC part of form DMC left. All right. And M is motion. All right. We go back to the monocular view of things. You can see motion with one eye, right? So we come on to relative motion. That basically means things that are further away look way slower, things that are closer look faster. Not much to it pretty basic. Last one is constancy. Constancy means that images change. It doesn't mean our perception of it changes. So if you let's say if you sat 15 feet away from me, right? And then you came inside a foot away from me. I wouldn't think that you're bigger a foot away from me. I would think that the same size object just moved a little closer. So basically just know that form, motion and constancy, you can always see that with just one eye. But depth is where you really need two eyes. All right. So we're done with all that. We're going to go to the other senses in general. So with senses, we know we have five. And so you know the normal senses you kind of talk about in elementary school, the site smell, sound, taste and touch. Well, for those five will use, but we're going to cut taste for now and we're going to add proprioception. So we have a smell, sound, touch, site and proprioception. All right. And so proprioception is basically just knowing the position of your body in space. So proprioception, knowing the position of your body. All right. So the main thing you got to understand is that all these senses adapt. So for example, with sound, you know, if you're hearing something you're adapting to the sounds, your inner ear muscles actually contract and relax. They contract and relax just so you know, dampen the vibrations and protect the eardrum. So with sound, you kind of downregulate sounds based on contracting and relaxing your inner ear muscles. All right. With touch, you've probably seen this all the time. We get desensitized at temperature. So for example, in the shower, you put the heat up a little bit and then five minutes later, it doesn't feel as hot. That's because you get desensitized to that temperature. All right. With smell, we get used to different smells too. For example, if I worked out a bakery, I wouldn't even notice the great smell after a while. It'd just be the same old already. And then the special one, remember proprioception, the one we just added. That is knowing the position of your body in space. So you get used to an altered view over time. So let's say, for example, you're hanging upside down and then, you know, you're looking around for a while, your eyes will get used to that upside down view. Also, I suggest don't hang out upside down for that long. They get used to it. Be normal. All right. All right. So up until now, we've seen down regulation. Sight is the only one that has both up and down regulation. All right. With sight, there's down regulation when you're adapting to the light, like your pupils restrict. But there's up regulation when you're adapting to dark and your pupils surprise. Die late. So what sense is the only one that can both up and down regulate? Five seconds. Four, three, two, one. Sight. Yeah. Good job. All right. So we talked about touch a little bit, but the adaptation of touch is a great concept. So before I get into Weber's Law, I'll talk about the just noticeable difference. All right. That's a threshold where you notice change. So Weber's Law, they find out about the K constants in regards to this just noticeable difference. By the way, from now on, I'm going to call the just noticeable difference JND. So the formula for Weber's Law is the JND divided by the initial weight or intensity equals K, the constant. So Weber's Law, it's, as you can see, it's just a ratio. See how much change compared to the original weight is necessary to notice a change. So the JND is a threshold where you notice change. Weber's Law is the JND divided by the initial. All right. So for example, if I lifted a rock, that was 10 pounds. And then let's say I lifted another rock, it was 11 pounds. I didn't really notice the difference. But I lifted another rock. It was 12 pounds. And I definitely did notice the difference. Then let's first find the JND. Then we'll find the Weber's Law constant. So 12 pounds notice the difference. All right. That's a change of two pounds before you notice something. So the JND, simple as that, it's just two pounds. Now we know the initial was 10 pounds. So to get Weber's Law, we do the JND divided by the initial. So the K constant is 2 divided by 10, which is 0.2. And just know the K constant has no units because you're dividing pounds by pounds. So yeah, don't let them trick you with that either. All right. So another important thing to know about Weber's Law, we don't only use it for weight, we don't only use it for anything we touch. You can use it also for sound. Let's say I mean, I can compare technically a whisper to a scream in this scenario. Weber's Law would apply just the same. All right. And another little tip, but no, since Weber's Law is just a ratio, it's going to be a linear relationship. So if there's a question about Weber's Law that showed different graphs, it's a linear relationship shouldn't be too bad. Now I'm going to jump into something similar, but also different. And it confuses a lot of people. And that's the absolute threshold of sensation. All right. So just off the bat, know the absolute threshold of sensation is different from the JND. All right. JND is one concept. Absolute threshold of sensation is another concept. So by definition, let's talk about what the absolute threshold of sensation is. That's the smallest amount of stimulus needed to notice a stimulus 50% of the time. So why are we mentioning 50% of the time? Well, there's differences amongst different individuals. Some people are more sensitive than others. And then there's differences in you. Maybe one day you notice something, then next day you don't. So by saying the smallest amount of stimulus to notice the stimulus 50% of the time, we cover our bases. And we can talk about reliably perceiving something. And as I mentioned before, absolute threshold of sensation differs amongst individuals. What does that mean? Well, it's subject to changes. Maybe your expectations, your experiences, your motivation, how alert you are, all that stuff, that can all affect it. So even though it's called the absolute threshold of sensation, don't think of it as some super hard and fast rule. Honestly, Weber's Law and JND is more of that like hard and fast rule. Absolute threshold of sensation can change. And that's basically a part of the definition. So moving on from all that on touch, on tactile sensation, on Webers law, let's talk about how you think, alright? So there's two different types of processing You should know of that's bottom up and top down So bottom up is when you get sensory information as it's coming in you build from the small pieces and you build big pieces So right now, let's say you're listening to this podcast You're building these words you're building an idea you take each word you construct it into a full idea That you'll use to get a 528 on the MCAT, right? Alright, so bottom up basically build from the bottom up you get those small pieces and you build bigger ones Top down is when you have preset ideas in your mind and you use those to interpret a situation So probably the best example of top down processing is when we read texts So we kind of just go over typos and text and that's because we take that contextual information that we've used All the information that we already have and we make an idea of what the sentence we think will be So we kind of just run over typos and ignore it all so top down you build from preset ideas bottom up You get the information as it's coming you build an idea as you go all right So the last of the conceptual psychological stuff I'm gonna be talking about is just salt principles and There's five laws really care about that's closure continuity proximity Pragnans and similarity so I'll go over the five just all principles again. Those are closure Continuity proximity Pragnans and similarity five laws All right, so similarity that's when you group similar things together So let's say I have a column of squares a column of circles another column of squares another column of circles I'll analyze a pattern based on columns. I won't look at the rows and be like oh, there has to be a pattern here No, I know there's a pattern in the columns and I'll interpret it as such because they're all the columns are similar All right now we'll go into Pragnans. That's when you reduce something to the most simplistic shape So Pragnans is actually a German word. That's why it sounds so weird. It's P R A G N A N Z It means concise and meaningful so the most common example is the one of the Olympic rings You see them as five circles, right? Not some intensely complicated shape filled with semi-circles all that stuff No, you just think of it as five different circles. That's Pragnans. You're reducing it to the most simplistic shape So proximity is pretty simple pretty obvious things that are you know close to each other are grouped together All right, and then we'll go on to continuity Basically it says you can make a continuous line whenever you can So let's say I see a hundred dots in a row But there's some dots on top of it and there's some dots below it But in general that we just see a hundred dots in a row You naturally organize those hundred dots into a continuous line So you make a continuous line and you distinguish it from those other dots All right, and the last law is closure and that says that basically When you see objects that are grouped together you kind of see them as a whole So let's say you know you want closure So let's say I have a circle and I made it with disconnected lines but The spaces in between the lines are really small So you still think of it as a circle, right? You still get the concept so you still think okay, even though it has disconnected lines I know what he's going for it's a circle All right, so next we're gonna jump from all these sensory things to the vestibular system The vestibular system is Mostly in the inner ear and it does two things balance and spatial orientation So just kind of getting your balance and your your sense of where you are and to be honest There's some things that really can't put into audio form and The actual physical shape of the vestibular system is one of them That's something I think you would have a much better understanding if you looked at it You know in a book or whatever online Despite that I'm still going to describe it the best I can obviously and I still will look at the order and talk about the function So we'll jump right into it First I'll talk about the semicircular canals in the vestibular system You had to know a few things here. There's three canals the posterior the anterior and the lateral So that's back front and middle so all three canals are orthogonal to each other That means they're at right angles to each other so one is on the x axis one is on the y axis and the last one is on the z axis And I could definitely see an discreet question being made out of the angle of the semicircular canals Just know that they're orthogonal alright alright, so the semicircular canals they're used for direction of shift and strength of rotation And it does so with this liquid called endolimp endolimp is a super potassium rich fluid It's you know, it's super rich in potassium just so it can start those action potentials So endolimp is used in those semicircular canals It's used for number one direction and number two the strength of rotation So how much are rotating but it's also present in the cochlear duct for hearing That's not really related to balance and vestibular system. You'll get into that maybe an episode or two from now Just know endolimp is the fluid in semicircular canals and you've definitely experienced the effects of endolimp So let's say you know you're spinning around in a circle and then you just stop right you still get really dizzy You feel like you're still spinning that's because even though you stop spinning your endolimp. It's a liquid It's still spinning so you get a little jazzy and you know you indicate to your brain you're spinning even though you're not All right, so next up in the vestibular system are the auto-lithic organs These are for linear acceleration and head positioning So if you remember with the semicircular canals I said that is the strength of rotation and the direction of shift Autolithic organs have to do with linear accelerations so straight forward or back and head positioning So semicircular canals just think of the word Circular you know that has to do with rotation shifting directions. Autolithic organs are just straight up up and down All right, so the most important thing you know about Autolithic organs or how they work Specifically in regards to the calcium crystals they have so they have calcium crystals that When they get pulled they tug onto a hair cell and it causes an action potential And the hair cell gets pulled if you do something like from lying down to standing So next up on the physiology aspect of this episode is sight and there's a ton of vocab words You need to know here. I'll definitely define them, but just as with the vestibular system open a book look at it a few times It'll give you that great understanding if you pair it with the podcast So the first layer that light hits Conjectiva all right, that's a super thin layer of epithelial cells The conjunctiva basically the whole point of it is it moisturizes your cornea and it helps protect it from friction So your eyes are just open to the world you need the conjunctiva is kind of like an extra layer to help you Survive I guess all right next up is a cornea you've probably heard of this the cornea is curved and it's clear Basically what it does is it bends the light and it focuses the image on the pupil all right So right behind the cornea is the anterior chamber anterior meaning the front chamber It's filled with aqueous humor. Just no humor means liquid if you ever see it in a medical you know textbook anything like that You'll probably see it around I might say it a bit humor is liquid so the anterior chamber It's right behind the cornea filled with that aqueous humor and the aqueous humor Basically what it does is it provides pressure so keeps the shape of the eyeball and then right behind the anterior chamber is the pupil I mentioned the cornea focuses the image in bends the light to the people So we get to that part the people so the people can get bigger or smaller It depends on the degree of iris muscular contraction or relaxation So in the middle of the people is the iris and the iris is what your eye color is based on so if the iris Relaxes your pupils die late if the iris constricts your pupils Constrict so if you've ever gotten your pupils die late at the doctor, you know, that's you know what I'm talking about the people Basically it houses the iris the iris is able to change the amount of light that enters the eye by changing that size of the people So right now so far we had the conjectiva the cornea the anterior chamber and the pupil So we're gonna jump into the next one, which is the lens the lens is behind the people it bends the light So goes to the back of the eyeball So just like the cornea bent the light to get to the pupil the lens is behind the people and bends the light to get to the back of the eyeball So the lens basically just shuffles it a little further So behind the lens is a large space that space is called the vitrious chamber. It's filled with vitrious humor Which you know unlike the aqueous humor the vitrious humor is more of a jelly like substance aqueous humor is more of that liquid And so the vitrious humor it kind of does what the aqueous humor does So it provides pressure to the eyeball But it also does another thing and that's providing nutrients as well And the next thing is pretty important and that is the retina the retina lines entire back the eyeball It's tinted red so when flash from a camera bounces off the retina and directs back to the camera you get those red eyes in some pictures So the retina is where you'll have a lot of questions because it pertains to rods and cones So off the jump just know the basics Rods are for black and white cones are for color so the thing of cones, you know first two letters to CO Just like colors first two letters to CO cones color rods black and white So inside the retina which like I said it lines the entire back of the eyeball is the macula and That places unique because it's super rich in cones which means color But only has some rods inside the macula is an even cooler place and that's the fovea and the fovea is cool because it has all cones and zero rods So the retina has the macula a place with a ton of cones and some rods and the macula has a fovea a place with all cones and zero rods So what do the rods and cones do so I mentioned earlier rods are for black and white cones of her color and what they do is They display this information to your brain by taking that physical waveform we see in light and they transform that physical waveform to an electrochemical impulse and that rides up your optic nerve goes all the way up to your brain and you interpret that that electrochemical impulse as light And another thing to know about them is a quantity so there's 120 million rods and there's only six million cones And most of the cones are in that fovea. Remember that unique place in the macula in the retina So that means what there's 20 times more rods and cones So with a high quantity, it's obvious, rods are more sensitive, all right? They're more sensitive to light than cones. The tell us if light is present or not, but cones, they have an advantage over rods, and that's what they have a fast recovery time. So rods are pretty slow, and you've definitely seen that in your own everyday life. Let's say you turn your bedroom light off and you walk to your bed, you're blind for about a minute, you know, a minute or two, while your eyes are adjusting to the dark, that's just your rods adjusting to that lack of light. And it takes a minute, you know, you don't immediately get night vision. So rods are good because they're sensitive to light. They know if there's either a light present or not, and cones are good because they have that fast recovery time. They can just bam, say that there's a color or there's not. And then lastly, I'll conclude with just one vocab word, and that is the blind spot. So remember I talked about how the rednut lines entire back the eyeball, well I lied. There's a little bit of the back of the eyeball, it doesn't line, and that's the blind spot. That's because that's where all the nerve fibers come in, and that's where they form the optic nerve. And it's basically a tunnel from your eyeball to your brain. So first episode is gonna be pretty quick. I just wanted to get a little taste of Grow Series this MCAT content review podcast. So we reviewed over some stuff, you know, sensory processing, the stimulus system and vision. But like I said before, it's a rough overview. So use this kind of as a supplemental tool, really hammered all home with additional content review. And just like that, we are done. So thank you guys for listening to this first episode, and see you on the next one.