Sensory Systems

this is video 2 in our series on sensation in this video we're going to focus in on specific sensory systems we'll spend most of our time on the visual system and the auditory system we'll touch on some of the other systems but we'll leave class for most of those discussions this video is meant to be an introduction a jumping-off point for a classroom discussion so we'll start with the vision the visual system in human being is our dominant sensory system meaning if we have a discrepancy between for example what we hear when we see our brain will usually bill with what we see 70% of all of our sensory receptors as human beings are found in the eye so we can see that it's our dominant system let's take a quick look at the anatomy of the eye these are the structures that we'll won't be able to identify and label let's scroll down let's look at this picture of the eye here and see the parts that we're going to need to label with the cornea which is the outer covering and the lens that we see here and the lens is going to focus the image onto the back of the eye speaking of the back of the eye this layer of cells here this yellow layer is the retina and it's in the retina that we have our receptor cells are rods and cones that are going to actually be stimulated by the energy from light and transduce that energy into neural impulses so if we're looking at this and we have maybe an image out here and we're looking at a tree that's my nice drawing of a tree and then the light from this tree comes into the eye and the the light comes in and the lens is going to focus this image so that it falls the back of the eye and we see it's going to be flipped upside down if you know from physics how it lenses work yet in our brain our perception of this is that it's right side up so again we process that information our brain turns it around for us but this focal point sometimes can be shifted meaning if the shape of the eye is shaped to oblong or it's maybe it's too narrow then it's possible for the focus of this image to be maybe too short and in front of the retina which we call nearsighted or maybe slightly behind which we'd call farsighted and of course we wear corrective lenses to bring that image or push it back so it falls right here on the retina so we can see things and they're not blurry a couple of the things we want to point out here the fovea centralis or the fovea is the center of our visual field and looking up at this diagram may be a little cleaner the fovea and it's here that we have our highest concentration of cones and we have the sharpest image but I also want to point out this area where the optic nerve leaves the back of the eye it's also our blind spot because for at this part right here we have no receptor cells all we have here are all the axons from all the other cells that are leaving the back of the eye so in this spot right here we have no vision and we actually have an empty spot yet we don't see it in our visual field if we kind of fill in the blanks and of course we would want to be able to identify the retina in this back portion of the eye and let's zoom in on the retina and look at the cells that make up the retina so this is zooming in and we see we have two very important types of cells we have our rods and our cones we have our rods and we have our cones and rods are better for lightness versus darkness and it's responsible for having good or bad night vision animals that are nocturnal see well at night have lots higher concentration of rods and cones are for color and in the central of our visual field and the fovea stand trial so we have a large concentration of cones for very sharp images so light would come in and strike one of these cells and stimulate it to fire an action potential and fires an action potential which moves up through these inter neurons and the message then transfers down the optic nerve and that's where we have to go back into the brain now each of our eyes has a right and a left visual field our right eye has a right visual field and a left visual field and our left eye has a right visual field and a left visual field and this diagram the right visual field is in blue so let's follow the right visual field the right visual field of the right eye since it's information to the left occipital lobe or visual processing and the right visual field of the left eye in blue here fall since it's information to the left hemisphere of the occipital lobe and right here there's a little crossover if it needs to switch over sides and the thalamus routes those sensory neurons to the visual system to the back of the brain for the occipital lobe for visual processing once these elements of our visual system get to this visual processing Center different parts of it are kind of partial doubt for processing and we have very specific receptor cells in the brain that are sensitive to certain features like horizontal lines versus vertical lines we have some features that are sensitive to movement others to depth and others to color so if we think about our visual experience being multi-dimensional like this it's not that we see the whole image we see components of the image and each image has form a ground versus a background versus foreground and the horizontal and vertical lines has motion to a color and depth and we process each of these elements of the visual experience in parallel separate from each other it's not that we process form and then motion and then color than depth we process depth color motion form and we do it in a parallel Siri and parallel rather than series and then we combine those to create the image what's interesting about that is if one of these systems fails we get a very unique visual understanding if you couldn't see color obviously you'd have your image or that color but what if you couldn't detect a motion and you get form color and depth but not motion then you wouldn't be able to see things as they're moving and there are examples of that happening and class will come up we'll talk about some more examples of how this system can kind of go awry and also the fact that there's certain parts of our brain that seem to be dedicated for recognizing certain types of features such as faces now I don't to spend too much time in this video we will talk about more in class there are two different theories on color vision and human once called the cry the trichromatic theory which supposes that we have three distinct receptors in the retina for green blue and red and that's the combination of the firing at these receptors that we can perceive all the different colors that we see in our visual experience but that doesn't explain all of color vision there's another theory the opponent-process theory which brings to light the couple of other phenomenon in our color vision system as the idea that we have two opposing color pairs or three posing color pairs yellow and blue red and green and black and white and that we have a hard time seeing both of those colors at the same time the idea would be that as the as we excite the red receptors that we actually suppress the green and when we were sensing blue that we can't sense yellow and there's a little experiment that we're going to do in class with after images where we can see how that might manifest itself like I said this would be a discussion will happen class I just want to introduce the terms here so you had the terms as we move forward let's move over to hearing and the the first let's go over the anatomy of the of the ear we have the outer ear which helps direct the sound wave they're traveling through the air down the ear canal and we reach the end of the ear canal we have the eardrum or the tympanum this is a thin membrane that stretches across this opening and as a member that will vibrate with the vibrations of the air that are sound causing these three bones of the middle ear the incus or the malleus the incus and the stapes to vibrate and transfer these sound waves into a very mechanical movement of these small bones in the inner ear which then press on the oval window of this snail leg structure called the cochlea and it's inside the cochlea that we have the actual receptor cells for sound and a structure called the organ of Corti and up here at the top this purple structure this is another inner ear structure it's very important for our sensation of balance this is the are our vestibular system these are called the semicircular canals and we have on three different axes the X the Y and the Z axes this arch and there's fluid in here and as that fluid moves around there are receptor cells in there that give us information about the orientation of our head up down left right back and forth and it plays important in our sense of balance we have a couple nerves that lead out the year we have the the auditory nerve or the otic nerve right here that leads into the temporal lobe of the brain for interpretation of the sound and we have the vestibular nerve from the semicircular canals that send our the information to the brain again regulating our sensing our directional balance and of which way we're facing it was going up or down let's think about how this works when the vibrations from the air the sound waves come in to the ear canal they hit the tympanic membrane they cause it to vibrate back and forth which causes these bones to move back and forth which causes this bone and move back and forth which inside of the cochlea sends this vibrations that we're going to is very thin medium to air into a thicker medium of fluid and these vibrations in their very specific pattern of frequency and and then strength travel through the cochlea and we need to zoom into the cochlea to see what's going on in there so inside the cochlea and this is simplified we have a basal membrane that has many hairs on it so imagine if all these different hairs and as that fluid passes by it difficult these hairs to deflect and in the organ of Corti and the these hairs are attached to sensory neurons that when they deflect cause the neurons to fire and as to firing these neurons in the organ of Corti these hair cells that initiate the nerve impulses in the year the question becomes how does the ear kind of discern pitch and frequency and in volume and there's two theories that go with this about how that you're actually is working there's the place theory which says that we interpret pitch based upon where the vibrations occur along that membrane so in other words if they occur out here versus deeper into this sure that the place on the cochlea that's where the hairs are deflecting represents the different pitches the frequency theory says we interpret the sound by the frequency of the auditory nerve firing so two different theories and that both of them have some some elements that work together to explain how the ear works for further information on how the ear works I have a couple of videos linked on our webpage that goes into more details but for now if you know the basic physical elements if you can basically identify the anatomy and where the different things are happening that's probably enough for now for our psychology course now there are other senses and again we're going to spend time talking class talking about these some more than others but obviously our sense of smell and taste and we're going to late those two chemical senses - how they affect things like or how they're related - to memory we're going to talk a little bit more about the stimuli or sense of balance but our sense of kinesthetics or movement and how our body is moving in the concept of proprioceptors a very interesting idea here the proprioceptive the sense of knowing where our body parts are in relationships our other body parts which is a sense that we don't think about it's also very important to kind of how we relate to the world and we can we're going to read an excerpt from the man who mistook his wife for a hat where the case study is a woman who has lost this sense of proprioception and then of course our skin senses touch and pain the two we're going to spend a lot of time talking about we definitely need to learn about the gate control theory of pain and how we can go about maybe blocking pain sensation or even sometimes ignoring it and we have some interesting things to talk about there so with that said this is our preview video ends our preview video on sensation and we'll have another set of videos for perception you