Special Senses Lecture

0:00 in this lecture we're going to talk about the special senses the special senses include smell taste vision hearing in equilibrium unlike the general census which are found throughout the body the special senses are housed in complex sensory organs and are located in very special places for instance of a sense of smell a course is located at the top of the nasal cavity whereas the sense of taste is founding the tongue the epiglottis parts of the throat also vision of courses in the eyes hearing and equilibrium in the ears

0:48 now the sense of smell is the first one and this is the sense of affection okay and sensory receptors are chemoreceptors which means we're going to detect tiny little chemicals those chemicals are going to bind to the olfactory nerve cranial nerve number one and this is what's going to create an action potential or nerve impulse to the olfactory areas of the brain so sensory information travels along the cranial nerve one the olfactory nerve to the temporal lobe and the temporal lobe is where our sense of smell is located so what happens is odorants are going to

1:34 bind to receptors sodium channels are going to open depolarization occurs and the nerve impulse or action potential is triggered and if we take a look at this picture over here we can see the core perform plate if you remember that in the skull it didn't take up very much space but that was the part of the skull that had the little holes in it core performed means it's full of holes and the cranial nerve number one is what came through those holes so really when we talked about the cranial nerves we couldn't really see cranial nerve number one because they are so small almost microscopic are pretty much

2:22 microscopic and so as you can see they're going to come down through these holes you're going to have the olfactory epithelium right here that olfactory epithelium is going to have a coating of mucus although you think it's mucus but it's not okay that was a bad joke it is mucus and the purpose of the mucus is it's very sticky and the odorant molecules can adhere to the to the mucus and it's at that point that can come in contact with the olfactory hairs which are part of the olfactory receptor cells which then are part of the olfactory

3:12 nerve cranial nerve number one so adaptation and odor thresholds adaptation equals decreasing sensitivity in other words if you do cooking for instance there's times I'll be cooking something and you know it's it smells fairly good but if you go outside or another part of the room and then walk back into the kitchen although sudden it's like wow that smells really good that's because while you're in the kitchen your sense of smell becomes adapted to that smell and you might not notice it okay but if you leave for a

3:59 while okay they can kind of reset themselves and when you come back in you you again notice that smell so olfactory adaptation is rapid it's about fifty percent one second complete in about a minute now or threshold for odors is actually very low which means we only need a few molecules to be present in order to detect the presence of a smell and I don't know if you realize this but natural gas and I'm talking about the kind you cook with but natural gas like on your stove and what-have-you is odorless that's right it doesn't have a

4:45 smell to it you're like wait a second you know if the gas is turned on I can smell it well that's because again naturally occurring gas has no smell to it so the factories the refineries and a chemical called methyl mercaptan to the gas and this way we can detect that odor and we associate it with the gas itself even though natural gas has no order so it's kind of a warning signal because if we didn't weren't able to smell it at all you know we could have a gas leak not know it like you know a burner or something and cause an explosion or even

5:31 just breathing the gas fumes are toxic but the methyl mercaptan they don't have to put much in it's just a little bit because of the low threshold we have four orders and we are going to detect that smell now the olfactory pathways the axons from the olfactory receptors form the olfactory nerves cranial nerve number one that synapse in the olfactory bulb and again it's going to pass through the 44 aminah of the cribriform plate and the second order neurons are within the olfactory bulb and they form the olfactory track that synapses with the primary olfactory area of the temporal lobe and this is where

6:17 conscious awareness of smell begins and other pathways lead to the frontal lobe and that's Bradman's area 11 where identification of olders occur now I don't really want you to I guess get too worried about the Broadman areas okay but the fact that it's one thing to smell a particular smell it's another thing to identify it and know what it is okay and so that's in a different part of the brain and we typically refer to those areas is association areas now we're going to talk about the sense of taste and another word for taste is gustation and so taste buds on the

7:05 tongue are special organs of taste or the gustatory sense and receptors are classified as chemoreceptors in other words chemicals in the foods that we chew up are going to bind to receptors and create an action potential which is going to help us determine the taste and there are four basic taste sensations there is sweet salty sour bitter and a fairly new one that you don't see in the older books so in that's you mommy and well here I got a little video that might help you with you mommy so this guy walks in look at the pic of fine I'm like look buddy I don't want any trouble he's

7:50 like what are you chicken I'm like wasn't man effect I am chicken and bacon tomato lettuce little chipotle mayo and he's like are you think you're at stuff huh I like well the Chipotle males got a little bit of a zip to it but its taste pretty good he's like oh yeah tastes pretty good huh what would it taste like I'm thinking was this guy coming from well it tastes like tastes okay there's there's five different tastes technically you know there's a sweet there's sour salty bitter in your mommy that's kind of what I fall under cuz that's uh yeah a little more savory so I'm like it tastes like you mommy and he's like what I'm like my told joy

8:35 tastes like you mommy it's like don't go talking about my mommy and I'm like now it's not my mommy it's you mommy it tastes like you mommy he's like a buddy keep it up and I'm like whoa whoa whoa look here but you know I'm just not in the mood okay so I don't know after he threatens to kick my buns he finally leaves oh geez I don't know about this guy here but I'm glad he left I guess he just couldn't cut the mustard okay so technically it's pronounced umami it's a Japanese word that refers to a savory taste and if you want to

9:21 know what savory is well think about like chewing on meat meat has a savory flavor mushrooms have a savory flavor I mean would you describe me too sweet or salty or sour bitter if you do that you've either season the meat or it's gone bad or something like that but umami is is again savory and if we look over the picture here and I don't have it mapped out for mommy I've been having a hard time finding a good picture map of that but if we take a look at the tongue we can see where sweet is located and where salty is located off to the sides is going to be sour and toward the

10:08 back of the tongue is going to be bitter and most things that are bitter have kind of a toxic component to it it has a lot of alkaloids which make it bitter if you've ever eaten things like dandelion greens or arugula or any of those type of vegetables or leafy greens that have a bitter component to it now for us they're not toxic but a lot of things aren't like for instance if you chew of an aspirin it's very bitter most medications if it starts to dissolve on your tongue or if you have to chew it up it's very bitter okay and bitter things again in high quantities can be toxic so

10:55 that's kind of a defense mechanism that if it's really better you might gag in you might spit it out but like I said a lot of the leafy greens that tend to be bitter are not bad for us in fact a lot of animals like rabbits and turtles and things like that will will seek out these bitter greens and if you think about like a dandelion if you break it there's like a white milky substance that comes out that's the alkaloids but these animals will seek these things out and eat them because well a wild animal doesn't have access to a veterinary and if it's not feeling well and a wild animals are especially susceptible to internal parasites and so

11:41 if they eat these bitter things these alkaloids a lot of times that will either kill the parasite or make a very inhospitable environment for that parasite so the bitter area again on the tongue is toward the back and again it's kind of a defense mechanism now sensory information is going to travel along the facial nerve which is cranial nerve number four and that's going to innervate the anterior two-thirds of the tongue and it's actually a branch of the facial nerve called the chorda tympani nerve and what's interesting is the chorda tympani nerve its route kind of passes just behind the eardrum and sometimes if you're looking in

12:26 somebody's ears with a notice cope sometimes you can see the little shadow of the chorda tympani nerve going past that your drum and kavon an interesting phenomenon it doesn't happen often but it can happen where vibrations from the tympanic membrane can stimulate that that chorda tympani nerve and people can actually taste sound so and I know your question well what a sound tastes like well I don't know I've never had that happen but hopefully they're listening to some I don't know some pretty sweet tunes but and that one makes sense right and here are two thirds of the ton but anyway getting back to this again it's

13:12 kind of rare the next is the glossopharyngeal nerve which is cranial nerve number nine and that takes care of the posterior third of the tongue now one thing not mentioned on here is cranial nerve number 10 which is vagus nerve vagus nerve is going to innervate the epiglottis and again the epiglottis as you can see right here is a little flap again that covers over your Airways and it does receive taste information so you do taste as you're swallowing the food okay and so these nerves go to various parts of the brain eventually arrives at the gustatory cortex of the parietal lobe now one

13:58 thing I want to talk about usually when we think a taste buds we think of those little bumps on your tongue those bumps are not taillights those are what we call papilla and there's different shapes of papilla this is a filiform papillae and you ever have a cat lick you cats tongues are very scratchy and it's because they contain a lot of these filiform papillae and if you notice there are no taste buds associated with the filiform pillow over here we have a valet tour circumvallate papillae and the circumvallate papillae have the taste buds running along the sides here

14:45 and then if we keep going in a clockwise formation here we see the Foley eight but pila it's kind of shaped like a leaf sort of if you use your imagination but it's going to have taste buds along the sides as well so you can see taste buds are actually microscopic then we go over to the fungiform papillae it's called Funch form because it's kind of mushroom shaped and it also has taste buds associated with it and so we have about 10,000 tastebuds found on the tongue soft palate and larynx and it's found on the sides of the circumvallate the Foley eight in the

15:31 fungiform a pillow and it's going to have basically three cell types it's going to have a supporting cell and a receptor and basal cells and so this is what at a splint would look like it's an oval body it consists of about 50 receptor cells and it's going to be surrounded by supporting cells now here's the gross part coming out of the middle of each of these taste buds is a single gustatory hair and it's going to come up through the taste poor so it's kind of gross that you you actually have little hairs coming out to other taste buds on your tongue I don't know about

16:16 you but the thought of hair on my tongue kind of grosses me out but we do we have this little single gustatory hair sticking out and then here we have a basal cells and they develop into new receptor cells about every 10 days or so look at the physiology of taste we have completed app tation in about 1 to 5 minutes so try chewing food for a while after a while you start to lose the taste partly because you're you are kind of sucking out the good juices there but also because it's adapting ok your tongue is adapting and you're not really

17:01 noticing the flavor now we have different thresholds for taste that vary among the the four it says for primary taste I haven't changed that it is five primary tastes the most sensitive is going to be bitter or poisons okay and we would want to be very sensitive to that bitter or poison taste so that we don't intentionally ingest something that might harm us the least sensitive believe it or not is going to be salty and sweet and that would account for if you look at packaging on processed foods

17:47 there's going to be a lot of salt and there's going to be a lot of sugar at it sometimes they're not necessarily the first ingredient but they're up there okay so that's why the handsome insulting so much sugar to their products because they want us to taste it they want us to crave that food now mechanisms of taste the dissolved substances are going to contact the gustatory cares and again this is a chemoreceptor so the receptor potential results in neurotransmitter release and the nerve impulse is formed in a

18:33 first-order neuron so the first order neuron or first order gustatory fibers are found in the cranial nerves and we've kind of talked about this earlier but I kind of mentioned it again to reinforce it cranial nerve number seven the facial nerve serves the anterior two-thirds of the tongue again the branches the chorda tympani nerve cranial nerve number nine the glossopharyngeal nerve serves the posterior third of them and then we get the cranial nerve number 10 which is vagus nerve serves the palate and the epiglottis now signals travel to the thalamus or limbic system and also to

19:19 the hypothalamus now we talked about the limbic system what is the limbic system what's its function one of its primary functions if you said emotions you'd be absolutely correct and this is why we have have an emotional connection with food it also is very strongly connected to memory so and the same thing with a sense of smell to I didn't mention that but they both have a very strong connection to memory and this is why if you taste something or smell something that reminded you of grandma or your favorite person or something you ate a long time ago it they might bring back

20:05 you know happy memories or might bring back tragic memories or what have you but the bottom line is there is an emotional component to eating to taste now taste fibers extend from the thalamus to the primary gustatory area of the parietal lobe of the cerebral cortex and it provides conscious perception of taste now we keep talking about taste and again the tastes are going to be a sweet salty sour bitter umami but that is totally different than flavor like for instance if I give you an orange and a have you tasted what are

20:53 you going to tell me it tastes like well you'll probably say it well it tastes like an orange that's a flavor but if I say okay break it down you know is it sweet orange is a sour orange okay well it might be sweet if you got a good one it would be a sweet orange okay maybe if you put a little salt on it would be sweet and salty or if you got a little bit of the kind of the rind or the pith of the orange that tends to be a little bit bitter now those are tastes now here's the thing the sense of taste and the sense of flavor they are connected to or or i should say the sense of taste

21:40 and the sense of olfaction or smell that is what gives us flavor ok so the sense of smell the sense of taste is what gives us flavor and I want you to try this sometime if you can get ahold of some skittles or starburst starbursts are probably pretty good for this I'd like you to get one you know have a friend or somebody you trust handing you something you're going to stick in your mouth cut you don't have them pick one not tell you what it is hold your nose and close your eyes put it in your mouth chew it and see if you can tell what flavor it is chances are you're probably

22:27 not going to know the flavor you're going to taste that sweet you're going to taste that it's you know maybe sour okay but when you let go of your nose okay and choose some more now you're going to pick up the flavor because again olfaction has a strong connection to flavor and that's why like if your nose is plugged up food just doesn't taste right okay because you have to have that smell component okay the sense of sight the visual accessory organs of sight are going to include the eyebrows and the eyebrows

23:15 basically are there to help keep sweat from rolling down into the eyes one of my slides talks about it access shade but i'm thinking unless you're in the end at all and i got to get much shade from your eyebrows that seemed like a goofy thing your eyelids and your eyelids do a few different things one every time you blink the eyelids kind of wipe over the eyes to take off dusts and grit that might be on the eyes helps to close up the eyes when you sleep it protects the eyes so if something is going to poke you in the eye the eyelids will close okay so they do quite a few

24:01 different things the eyelashes again it's kind of a protectant mechanism something touches the eyelash first it's going to stimulate the blink reflex okay we also have the lacrimal apparatus the lacrimal apparatus is what produces tears now where do you think the tear ducts are or the tear glands let me let me rephrase that where do you think the tear glands are and if you can't just I can't see you but point to where you think the tear glands are now a lot of you have probably pointed to the corner of your eye toward your nose and that is not correct now tear ducts are found

24:47 there but the tear glands are going to be in the superior lateral aspect of the skull you know of the orbit of your eye there just behind the eye okay so it's going to be found in the the orbit and the skull upper outer quadrant there behind the eyeball and think about it like this the lacrimal gland is kind of like a rain cloud it's producing tears and you think about where clouds are and clouds are up above and through gravity it pulls the the rain toward the earth same thing here gravity is going to help flood tears over the eye to help nourish

25:35 it to help wash away dust in dirt and basically keep the I healthy there's enzymes in tears called lysozyme and they help to kill bacteria and things like that okay and then we have the extrinsic eye muscles nets allows for movement of the eyeball in the socket and so if you haven't already take a look at the video i made on the eye muscles now the eyeball has three layers we have the square of the choroid and the retina the sclera well let's take that word apart for a second here scoll

26:20 eres means tough and it's the tough outer covering of the eyeball so it's the outermost layer that extends anteriorly and eventually forms the cornea but it's the whites of your eyes so predominantly is the whites of the eyes the choroid is going to be your middle layer and that's rich in blood vessels the next layer the retina that's going to be the innermost layer it's the nervous layer that contains photoreceptors rods and cones and we'll talk about those in just a little bit the rods and cones are the photoreceptors and they are going to detect light and again when they detect light you're going to get an action potential and so the eyeball also has

27:10 two cavities we have a posterior cavity it's located between the lens and the retina and it's filled with a kind of a thick snotty solution that's called the vitreous humor okay it's real well is it thickens naughty if you've ever dissected an eye all maybe in high school you'll know what that kind of looks like the anterior cavity located between the lens and the cornea is filled with something called aqueous humor okay and aqueous means water so it's it's more of a watery fluid now one thing the eyes constantly making this fluid and we're

27:56 going to build up to a certain pressure if we go too high on pressures then well that's not good that's going to cut off blood supply it's going to do damage to delicate tissues and so we have to have a way of regulating that excess fluid and so right here we have what's called the canal of schlimm and again we're getting away from name so I'm sure they've changed that to a another name but the canal of schlimm here is a little opening that allows excess aqueous humor to kind of bleed off as the pressures enlarged if that canal if schlimm becomes blocked for whatever reason then pressures can build up in

28:44 the eye and we can develop glaucoma and in glaucoma is kind of one of the number one causes at least in the u.s. of blindness okay two sets of eye muscles we have the extrinsic eye muscles and the intrinsic I muscles the extrinsic eye muscles are external to the eyeball and control the movement of the eyeball and again take a look at that video I made and the intrinsic eye muscles control the size of the pupil in the shape of the lens and again if you've ever dissected an eyeball you know the lens is kind of rubbery I mean we're dissecting one in high school and it did it felt like a little rubber ball little

29:30 hard rubber ball and and guess what we did yes we started bouncing it around on our tables and because it's oblong it went all over the place but because it is kind of rubbery like that we can attach muscles to it and these are going to be able to pull on the lens or relax and let the lens go back to its original shape and this is going to help to focus light that's coming through that lens now as far as the pupils go now what did we learn about muscles what a muscles do they can only contract and relax so you know if we're going to have two different movements we're going to have to have two different sets of

30:17 muscles and that's what we're going to find here we're going to have our circular muscles and when they constrict that is going to make our pupil smaller but if we want to make our pupil larger then we're going to need another set of muscles we're going to relax the circular muscles and then the radial muscles are going to contract and pull that opening your pupil a lot more open and we're going to get a larger pupil from them so it's kind of stretching that circular muscle back out so we stretch the circular muscle out and then if we want to constrict the pupil then

31:03 we relax the radial muscles and the circular muscle constricts okay an able to unable to see a lights going to enter the eye and stimulate the photoreceptors and the nerve impulse carries the information from the photoreceptors along the optic nerve or cranial nerve number two to the occipital lobe of the cerebrum and on this brain we can see kind of the the pathway that light impulses would take it's going to start off after dinner is the I going through the optic nerve which is cranial nerve number two and here's the thing if we let's just take a look at one eyeball so

31:51 if we take a look at one eyeball the left or I guess which way should say is the 10 prol field of view is going to come in and it's going to go down the optic nerve it's going to stay on the same side of the optic nerve it's not going to cross over it's going to stay on the same side and then go down the optic tract from the optic tract it's going to connect up with the lateral geniculate nucleus of the thalamus and hook up to the optic radiations which then go down to the occipital lobe of the brain and it's our visual center now the nasal

32:38 view of the eye is actually going to come down it's going to cross over at the optic chiasm and go down the opposite optic tract to the lateral geniculate nucleus where then it connects up with the optic radiation and goes to the opposite side of the brain to the occipital lobe so it's kind of interesting how that do it does that it actually splits your your visual field up into almost quadrants okay all that information is reassembled back in the visual cortex to be able to see the way we do we see in this video we're going

33:25 to talk about visual processing so how our brain is able to make sense of what we're looking at so in most of the our body we have the right side of the body being controlled by the left side of the brain and the left side of the body is controlled by the right side of the brain so how does this work in vision so let's imagine that this rectangle that I drew is our entire visual field and if these two eyeballs were focused in at the center this rectangle so if they were both focusing on this purple line all they can see are these two colors so we have a ray of light coming in from the left visual field it'll hit the eyeball it'll hit the left eyeball and it'll kind of be bent a little bit by the lens it'll hit the right side of this eyeball and so the inner side of the eyeball so this side of this

34:11 the left eyeball and this side of the right eyeball is known as the nasal side because it's the nose would be right in the middle of the eyes so the nasal side is the side of the eyeball closest than those and then this outside part of the eyeball which is over here and over here is known as the temporal side of the eyeball because it's closest to your temple so this is the site closer to the temples this is the side closest to the nose so a rate of light coming from the left visual field we'll hit the nasal side of the left eye and a ray of light coming from the web visual field we'll hit the right I be bent a little bit by the lens and it'll hit the temporal side of the right eye so let's look at a ray of light coming from the right side of the visual field a ray of light coming from here would enter the right eye and it would be bent a little by the lens

34:57 and hit the nasal side of the right eye whereas a ray of light coming in would hit the left I'd be bent a little and hit the temporal side of the left eye so let's look at what happens next so the eye is basically connect is the brain via the optic nerve so there is an optic nerve that kind of exits the back of the eye and goes into the brain so interestingly the optic nerve from both eyes actually converge so they actually reach a point where they converge and this point right here where they converge is known as the optic chiasm so they kind of converge and then break off again and then move even deeper into the brain so this point where they converge is known as the optic chiasm so optic

35:43 chiasm let's look at how this information is transmitted to the brain through the optic chiasm the renas lining the back of the eyeball and we had this yellow ray of light hit the nasal side of the left eye and it hit the temporal side at the right eye so let's go ahead and trace this information to the brain so the information will be sent via axons through the back of the eye into the optic nerve and basically it'll come in and what it'll do is it'll actually cross at the optic chiasm and then go this way and what we also have is this ray of light will come in to the back of the

36:29 eye and it will actually go down the optic nerve but it's not going to cross so all light that hits the temporal side of either eyeball does not cross the optic chiasm so let's go ahead and trace this green ray so the green ray coming from the temporal side of the left eye is going to exit the back of the eye go down the optic nerve and it's just going to stay in place so it's not going to cross the optic chiasm whereas this ray of light is going to go through the back of the eye and it's going to cross over here it's an across the optic chiasm and go down to the brain and so what this effectively does is it actually takes the right visual field and allows all the information that's entering the eye

37:15 from the right visual field to go to the left side of the brain so this is the left side of the brain this is the right side of the brain so like the rest of the body all the information coming from the right visual field actually goes to the left side of the brain and all the information coming from the left visual field goes to the right side of the brain in this video I'm going to talk about photoreceptors photoreceptors within the retina this is a very back of the eye so just roll one out here we're

38:05 going to look at what happens to the photoreceptor when it's in the dock so here we have a sodium channel this is our photoreceptor now the sodium channel allows sodium ions which are positively charged to

38:52 enter inside the photoreceptor this makes the inside of the photoreceptor more positive so if we look at the voltage over time it's going to get more and more positive inside so I'm going to introduce a few rules that are really important when considering the visual system the first one is that a cell will release

39:44 neurotransmitter when depolarized all right for this cell is now depolarized when the voltage inside is much more positive that's what we call being depolarized so according to rule number one this cell will have to release neurotransmitter and there it is can at the bottom now let's see what happens when light hits the photoreceptor this channel is

40:37 controlled by what we call a GPCR which is a g-protein coupled receptor let's see just quickly how this works when light comes into the photoreceptor it hits this protein called an option now through a series of events which I don't want to go into here this controls whether the sodium channel is open or closed so when light hits this option it

41:30 closes this sodium channel this means it's sodium these sodium ions trying to get into the cell cart I shouldn't say that this is a cascade of events not just one single event so I want to introduce my second rule this is at light hyper polarizes photoreceptors and when looking at the visual systems you can get really

42:16 confusing so it's really important to remember these two rules and then you can kind of work things out from these principles so let's look at the situation where light hits a photoreceptor so here's our light and it hits the photoreceptor so this blocks off the sodium channel so there's nothing happening there now let's look at the voltage inside the cell if

43:09 there's no sodium going in then the cell will become more negatively charged so the cell is hyperpolarized and that's rule number two now if we look back at rule number one that sells released neurotransmitter when depolarized it follows that a cell won't release neurotransmitter when hyperpolarized

43:59 now let's have a think about this Oh transmitter neurotransmitter used is called glutamate which is an amino acid but it's a very common neurotransmitter in the bang not that it's important but it's got a structure that looks like this now one last thing there are two types of photoreceptors rods and cones rods kind of look like what I've shown here and there are three types of cones

44:46 cones that respond most to red light to green light and two blue line and then there are rods the may respond to very little light so they use the night vision and that's a summary of photoreceptors okay that previous video was from hand written tutorials com and I'd like you to check that out now that particular video was an older one I'm probably one of his first videos it didn't have the quality of his later videos and that might be something you want to check out especially when you get to a in p2 because there's a lot more physiology

45:31 also if you go on for nursing or health care he does talk about pharmacology and a few other things so hope we didn't bore you too much there like I said his other videos are much better but for some reason that this slide presentation didn't cover that and I did want to make mention of the photoreceptors and some of the physiology involved okay the sense of hearing there's basically three parts to the year we have the outer ear the middle ear and the middle ear contains three ossicles the hammer anvil and stirrup or malleus incus and stapes and then we have the inner ear now the

46:23 inner ear structure is concerned with hearing and its main organ is going to be the cochlea and it contains hearing receptors like the organ of corti and hair projections on the cells are mechanoreceptors in other words they respond to a mechanical stimulation and in the case of the cochlea it's basically going to be vibrations in the fluid within the canals of the cochlea that are going to cause a vibration of certain structures that will then vibrate and push on stereocilia or hair cells and create an action potential then we interpret is hearing

47:11 so the organ of corti looks like this we have the tectorial membrane we have the hair bundle which contains stereocilia we have the outer hair cell and our supporting cells and then here's our inner hair cells and these are going to be connected with the sensory motor fibers of the cochlear branch of the vestibulocochlear nerve which is cranial nerve number eight now as fluid begins to vibrate this tectorial membrane is of course going to move as it moves it's going to compress these these hair cells

47:57 and again an action potential is going to be created and go to the auditory portion of our brain so as you hear sound waves entering the outer ear causes the to panic membrane or eardrum to vibrate and the vibrating tympanic membrane causes the ossicles the little tiny bones in the ear to vibrate the vibrating stay piece causes the fluid in the inner ear to move and then moves the inner ear fluid bends the hairlike projections at the organ of court I'd like I showed you earlier and then activation of the organic or ty creates

48:44 nerve impulses that travel along the cochlear branch of the cranial nerve number eight again the vestibulocochlear nerve and it goes them to the temporal lobe now also found in the inner ear is our sense of balance and the receptors again our mechanoreceptors so they're going to respond to mechanical stimulation and they are hairlike projections and they're located in the vestibule and the semicircular canals of the inner ear this first one found in the vestibule is a receptor that's activated when the

49:31 head the head changes positioned so activation the receptor creates a nerve impulse the travels along the vestibular branch of the stimulatory nerve cranial nerve number eight too many areas of the brain including the cerebellum the midbrain in the temporal lobe and if you notice on this picture here we have these things called o toadlets with or litho mean stone odo means ear so ears stones and basically what they're going to do is give a little bit of weight okay so they're going to respond to gravity they're going to sit kind of in this gel on top of this Oda lithic membrane and also embedded over or I

50:20 should say embedded into the autolytic membrane are these hair bundles we're going to have Kino cilia and stereo psyllium and basically basically what happens here is if you tip your head down because of gravity these Auto lists are going to slide forward and when they do they're going to distort the ODA lithic membrane and Bend these hair bundles when the hair bundles are bent then we're going to get an action potential and that's going to tell us that we've been to our head forward whether we tipped our head backward now this also responds to acceleration for instance in your car when you accelerate

51:06 it's going to cause these odor lists to go backward okay and give us the sense of acceleration as you stop these Auto lists are then going to move forward and give us this sensation of deceleration so again as I said the movement of the stereocilia or Kennaugh psyllium results on a release of neurotransmitter into the vestibular branch of the vestibulocochlear nerve again cranial nerve number eight and now we have these other receptors they are small elevations within each of the three semicircular ducts we have anterior

51:52 posterior and horizontal ducts that detect different movements and we have these hair cells covered with copula which is a gelatinous material and when you move the fluid in the canal bends the cupola stimulating the hair cells that released neurotransmitter and so when the head moves all the attached to my circular ducts and the air cells move with it the endolymph which is found inside the ampulla here it's a fluid does not bend it or does not move I should say and so it's going to bend the

52:38 cupola and the enclosed hair cells so nerve signals to the brain are generated indicating in which direction the head has been rotated now here's the thing if you have say a glass of water and you have something floating on top of the water and you kind of spin the glass when you stop what's going to happen just the water stop automatically know it's going to keep going now if we start spinning in a circle and then stop one thing that's going to happen is the fluid is going to keep moving and then it's going to keep pushing on this

53:24 cupola and when it does we're going to get this constant this constant action potential that's telling us that we're still moving and that's what cream makes us kind of dizzy now the reason the room seems to look like it's spinning as a result of this stimulation the eyes are going to start moving back and forth so if you ever get a chance to try this you know put your lab partner in a in a stool or chair that can spin spin them around stop them and look at their eyes you'll see their eyes moving back and forth again that's what makes the room look like it's spinning but what's actually happy and that and again that will also add to the feeling of dizziness but what's kind of stimulating

54:10 that is the fluid that in the lymph pushing on the cupola and making you still feel like you're moving and that concludes our lecture