VideoPoints

• ••• • •• • ••••• • •
BIOL 4315 Neuroscience Tue Th 4-5.30pm - Neuroscience Lecture 18 Auditory System
Help Tour
© Distribution of this video is restricted by its owner
Transcript ×
Auto highlight
Font-size
00:03 So today's lecture is on the on auditory system, on the hearing.
00:10 when we talked about visual system, talked about the properties of sound,
00:14 light. And we're talking about the system we're hearing, we have to
00:19 about the properties of sound just and sound is? It's really our neural
00:25 . Yes. Um I'm not sure anyone else is having this issue,
00:29 I can't find it in. it's been activated. Oh I'll try
00:36 again. So it's neural perception of energy. We have sound waves that
00:52 traveling at the speed of sound, is 343 m/s or 767 mph.
01:01 faster than the fastest car you've seen by you, the traveling vibrations of
01:07 in the air, they consist of regions of compression and rarefaction of air
01:14 . So a good example is a a tuning fork. If the tuning
01:19 is just sitting there, uh then molecules in the air are equally distributed
01:25 . There's no particular pattern, there's sound wave here. But if you
01:31 the tuning fork, then you create in the tuning form. And as
01:37 tuning for is vibrating, it starts and compressing these air molecules essentially in
01:47 the waves of sound. The same is with the stereo speaker or with
01:56 ear buds, uh your headphones listening sound, what's going on as you
02:03 this Dira as this, this diaphragm moving and as this diaphragm is
02:09 it's compressing and rear fracking, rear other parts of their air. So
02:18 what it is. It's the air really from the speakers or from your
02:23 balance through the little movement of the . Now, human audible range,
02:31 only in 20 to 20 Hertz, Hertz, 20 to 20,000 Hertz.
02:39 why I say only because there are that can communicate in much higher
02:48 And anything that's above 20 kilohertz or Hertz is called ultrasound. And a
02:54 of fish herring dolphins will communicate and ways of perceiving sounds that are at
03:05 , much higher frequencies that we wouldn't able to perceive with our ears.
03:08 just don't have the neural mechanism to the vibrations that are faster than 28
03:16 . Infrasound is everything below 20 Hertz you have uh equivalent of car
03:25 a slow vibrations, 20 Hertz or cycles per second. Uh subwoofer,
03:31 you look at some of the when you're shopping for speakers or computer
03:36 , it will say, oh, goes to 10 Hertz, it goes
03:39 four Hertz. So some of the will reproduce the sound below our audible
03:49 , we can adhere it. But you have experienced a really powerful symbol
03:53 you actually can feel the movement of molecules but not through your ears,
03:58 rather through your somatic sensory system that study in the next uh couple of
04:06 . Intensity is loudness. So how is the sound? So if it
04:11 a low intensity, this wave is to be small. If it's high
04:17 , it's really loud, it is to hear something like a volume.
04:23 frequency is a pitch. So low is low pitch and high frequency is
04:30 pitch, that's that's different. And can have low pitch and low intensity
04:38 low pitch and high intensity. So are the two qualities important qualities of
04:44 sound wise. Now, this movement the air enters uh our ears into
04:54 outer ear, which consists of the the outside the auditory canal also referred
05:02 external auditory, which is part of outer air. And finally, those
05:09 vibrations will start moving the titanic Titanic membrane is like a timpani,
05:15 big drum. So this is your drum membrane. The movement of that
05:20 drum is going to move, the are located in the middle air which
05:25 then going to move the oval window is on the cochlea portion of the
05:34 cochlea para. So the top portion is the vestibular apparatus and the snail
05:40 occur uh structure. Here is the , OK. And cochlea humans is
05:46 a size of a p like green . Uh so, and then everything
05:54 is from the oval window in the is a part of the inner
05:59 So this is the three major middle and inner ear divisions. Then
06:07 have uh the gestation tube that is in to this region. You can
06:14 it's in the air. The function the eus station tube that goes in
06:18 kind of in the back of of your throat is to equalize the
06:24 . So you will notice that when , for example, fly or even
06:28 drive a car and up the mountain down the mountain, the pressure changes
06:33 your ears get plugged up and on airplane, you'll see people blowing their
06:40 and opening and some people chew chewing not to have their ears clogged
06:46 And that's because the pressure difference is you change the altitude. And so
06:50 the station tube and through the opening movement of the obstacle bones and the
06:56 , we can actually equalize the pressure the outside and inside. And that's
07:01 because if you can't equalize the pressure how it changed in the airplane cabin
07:07 a high altitude, you it's going be very painful. So uh now
07:16 also a common side for ear gestation tubes. So, when you're
07:20 Children, sometimes, oh, I my child or my, you
07:24 my friend's Children had their tubes And that's because it's a very good
07:30 . It's very moist to station And it's a good spot for bacteria
07:35 viruses to gather and cause infections. it causes infection causes the infection all
07:42 the station tube, including, of , the middle ear ear and it
07:47 affect the earing. And then if infections are very, very frequent
07:53 and some Children, they can if you don't hear, you don't
07:58 . So, one of the alternatives those that suffer from chronic ear infections
08:04 their childhood is to replace the station with an equivalent of a uh of
08:10 device of a plastic tube like which is not a very good environment
08:16 bacteria and viruses to grow. And , you know, if you don't
08:22 , you don't learn. So if child for two years or three years
08:26 that critical period of development, very part of their life don't hear as
08:31 or don't hear in one ear because the infections. That means they are
08:35 focusing, they're not absorbing that sensor as well as their peers and they're
08:41 learning as well. So it could a tradeoff for some parents. Um
08:45 gonna have a surgery so that my can learn and not repeat these infections
08:50 can lead to some other things If it's a chronic infection in that
08:55 , obstacles are the smallest bones in body. And uh when you have
09:00 movement of the titanic membrane that will the three obstacles, the maus anus
09:06 sta and uh the inner ear inside is fluid filled chamber. But what
09:14 are going to do these obstacles because are interconnected, they have ability to
09:21 . So they have quite a bit torque. It's like they're jointed with
09:26 other, right? They can actually movement, small movement of the air
09:31 now can be amplified into much larger of the oval window through the group
09:38 the three interconnected os bos cochlea is snail like structure. Uh If you
09:48 to take this snail like structure here unroll it on the tip of the
09:58 , we have what is called apex a rema. And here you will
10:07 the base of the cochlea. So base of the cochlea is the closest
10:13 , to the oval window, the , this is moving and down
10:19 you also have a round window and there is an a certain distribution of
10:28 sensory cells called hair cells in a manner along the cochlea that creates the
10:37 see a tonotopic map. And now this is another interesting concept when you
10:45 about obstacles about to mention that you see that obstacles uh are surrounded in
10:53 area by stas muscle and tensor tiny . OK. This is important,
11:04 muscles can contract or they can relax guess what happens if these muscles
11:12 there isn't as much free movement of obstacles. But if they're relaxed,
11:19 area allows for more movement and more between these obstacles and therefore activation of
11:26 oval window. OK. So think uh this thing, you may have
11:32 thought about it. What happens if hear a really loud noise? What
11:38 you typically do? Close your OK. Your hands are tied,
11:45 do you do? OK. Your is fixed to kind of move your
11:55 . You, you squinted is did you do that on purpose?
11:59 you notice that sometimes when, when hear a loud noise, they not
12:03 kind of try to cover their but they do this like this kind
12:07 a thing. And if so your were tied, you can do it
12:12 your hands, you can do And you'll notice that even if there's
12:16 noise in the room or the it will quiet down a little bit
12:20 you do that and that's called attenuation . So when there's really loud
12:26 you will have the contraction of these and therefore the stiffening of the movement
12:33 the obstacles. And that's a protective so that you don't rupture the air
12:39 or you don't rupture the oval window leading into the cochlea. Ok.
12:45 basically, it's a, it's a by which you try to attenuate.
12:50 that's what it's called attenuation reflex, , loud noise. It's important because
12:56 noise will kill your hair cells from cochlea. And that will lead to
13:03 loss and cochlea do not regenerate. we talked a little bit about olfactory
13:09 neurons and you lose the sense of and then you actually regenerate them.
13:14 regrow the sensory cells from the cochlea not regenerate. So if you have
13:21 complete loss of hearing in one there's no going back and regaining that
13:27 a few months later. But years , I learned the hardwood uh scala
13:33 . If you take this basically cochlea put it, cut it in the
13:37 section in the top, you'll have chambers. The top chamber is calla
13:42 , this is scala and scala and media will contain the organ of and
13:49 is where the sound transduction takes place well as three of the. So
13:55 gonna look into this anatomy with a bit of a zoom and view here
14:02 the two chambers uh on top and bottom, the, the Sibu and
14:07 timpani are filled with para limp and is similar to the cerebral spinal fluid
14:13 we described even at the beginning of course, which basically has low potassium
14:18 the fluid and high sodium chloride So is paraly endo limp, which is
14:25 scala media and this is an easy scala media is in the middle.
14:30 you can never miss that on the . Now, if you look,
14:33 you miss uh the stimuli or that's another story. The stimuli is
14:38 to remember because the stimuli is on , it's closer to the vestibular
14:44 That's another way that you can remember , which is which media is in
14:47 middle of a stu vestibular apparatus. you remember the structure of the snail
14:52 then the vestibular apparatus on top, that the scallop vestibular is the tom
14:58 . But the Scalia is filled with limp and endolymph is unlike cerebrospinal fluid
15:10 of high sodium pendulum has very high levels of 115 milli molar and very
15:18 sodium. And this unusual high concentration potassium indicates that the signaling in the
15:29 medium with the organ of corti is be through the fluxes of potassium
15:36 As you'll see later. Number number two, you have to build
15:40 that gradient and that gradient of high is being produced by striar, which
15:47 sort of an endothelium lining of the and media that is generating uh very
15:54 levels of potassium and establishing that gradient the with the active transport. So
16:03 is the tonotopic map if you recall the room and in the L G
16:12 and the primary visual cortex, we point by point representation of the visual
16:21 of view and we call this retina map. So this is point by
16:28 representation in here, if you we talked about the apex,
16:36 which is the end apex and here this is the base. OK.
16:43 , the the best analogy that can given is the way to remember.
16:48 is the cells that are closest to oval window, closest to the base
16:54 most responsive. Those hair cells are responsive to high frequencies. You
17:00 move over a little bit farther from the window and it's slightly lower
17:05 That means the hair sauce or the of. And this part of the
17:10 is gonna be most responsive to eight . This one is four kilohertz,
17:14 kilohertz, one kilohertz 500 all the to 20 Hertz in the very,
17:21 apex of the cochlea. So in case, the cochlea Has a tonotopic
17:31 . So it goes from 16 kHzertz kg Hertz All the way to 20
17:41 over here. So there is this of cells and the map is to
17:48 topic. In other words, it's the localization of sound that we're talking
17:54 . The sound is coming from It's coming from there. We'll talk
17:57 that a little bit in this, this lecture, but it's the tones
18:01 the responsive of the cell to the . Uh This is where the oval
18:08 is. And the best analogy that still haven't come up with a better
18:15 is when you watch the Olympics, watches Olympics. Um, that's probably
18:23 only time every four years, everybody gymnastics. And as they watch
18:30 there's one um, um, performance their gymnasts do with the ribbon.
18:40 . And if you notice they have ribbon and the ribbon has a stick
18:44 what they do is they move their like this kind of a fast.
18:49 what it does it creates a pattern looks like this. In other
18:54 the further away you are from the , the more that ribbon flares and
19:00 mechanical movement. And so here you fluids surrounding these cells and there's going
19:09 be a displacement of the membrane, going to be a mechanical movement and
19:15 mechanical movement, the closest to the is the highest frequency just like it
19:20 be the closest to the very end the stick. But by the time
19:25 reach the end of that ribbon, each reach the end of the
19:31 the mechanical movement is much slower. that's because this movement of the sta
19:38 the oval window will move the fluids the three chambers. And as it
19:46 the fluids in the three chambers, going to displace the basilar membrane.
19:52 this is the basilar membrane here. on top of that basilar membrane,
19:57 have these supportive cells. This is organ corti and you have the hair
20:03 and the hair cells, they have , they have these protrusions like
20:11 And these protrusions can bend one way another depending on the displacement of basal
20:20 into the up position or into the position. And as the basil membrane
20:26 displaced, you can see this is displacement of the stereocilium is in this
20:33 . If there is a displacement of basil membrane, the stereo is going
20:38 shift and bend in one direction or other direction and how this is
20:45 So you have sin soil wavelike movement air molecules that starts moving. The
20:54 , airdrome starts moving the ossicles, start moving the oval window, movement
21:01 the oval window starts moving the fluid the other side of the oval
21:06 So now you have the movement of fluid as the fluid is moving,
21:10 displaces the basal membrane up down, down. If it's high frequency,
21:17 goes up down, up down. it's low frequency, it goes up
21:20 , up down, right, it out that when it goes in one
21:26 up and stereo CIA bends into the , for example, is shown
21:32 it will actually cause a depolarizing receptor . So these cells, hair cells
21:39 receptor cells, they don't produce action , they produce graded receptor potentials.
21:50 . If the stereocilium now bends in opposite direction, when the basilar membrane
21:55 down that results in a hyper So now this sinusoidal movement of air
22:07 movement of the fluids, displacement of of the CIA one direction you have
22:15 , hyphy depolarization, hyper depolarization, , you get a sinusoidal electric response
22:24 the form of the receptor potentials in hair cells. And you can see
22:29 there is one row of inner hair and three rows of outer hair
22:37 And this is another demonstration of that anatomy. This is electro uh microscope
22:45 that shows these stereo that are protruding are embedded and are being held on
22:53 Tector membrane. So, tectum Tector roof membrane. Ok. So that's
22:59 they're attached to and they're sitting on of these supporting cells here. And
23:06 have again three rows of outer hair and one row of inner hair
23:13 And they get contacted by the spiral Neurons or spiral gangrene cells that form
23:23 8th cranial nerve. And in the cochlear component of the eighth cranial
23:32 , which if you remember from the is the Sibu cochlear nerve. So
23:37 is the cochlear component of the cellular nerve comes from the cochlea, in
23:43 , mostly from inner hair cells, also from outer hair cells. How
23:53 the sound and the movement or displacement the fluids get converted into a receptor
24:01 ? So, in the retina, had activation of photo pigment and it
24:10 a metabotropic signaling that changed the potential the photo receptors. So it was
24:20 . We talked in this class about . So we talked about receptors and
24:25 . So the Ligon gated receptor we talked about voltage gated channels.
24:31 these are mechanically gated channels that are Trip A one or TRPA one.
24:43 there are channels in this case that potassium channels, the potassium pro
24:51 And when there is displacement of stereo one direction that displacement that mechanical movement
25:01 actually open up potassium channels. And potassium channels of the adjacent stereo are
25:10 interconnected with what are called the tip . So when this potassium channel
25:16 it's not only the bending of the that will encourage the opening of this
25:21 , but also the movement through the link will encourage the opening of the
25:26 channel. So it's it's going to opening because of the bend of stereocilium
25:31 of the pull of the tip link the next channel that is on the
25:37 stereocilium causing a significant influx of potassium endo limp is loaded with potassium.
25:46 that's where you have the stereocilium sitting by the limp. OK. And
25:54 potassium causing depolarization, opens voltage gated channels and now causes the release of
26:05 or neurotransmitter of the spiral gang There's no action potential, there's depolarization
26:13 that there is a lot of a lot of calcium more vesicles get
26:18 , more depolarization. It doesn't mean action potential. If it's less
26:23 it's less depolarization. So, excitatory and really, you're controlling the release
26:31 this depolarization in the absence of this . Now, also I have here
26:38 question for you. What is the potential value in the hair cells?
26:42 you remember such thing as nast equation equilibrium potential? RT Z F log
26:50 potassium in this case, on the versus largo potassium on the inside.
26:58 . So uh but you'll see that you have the changes in the inside
27:03 outside potassium concentrations, it will also change the equilibrium potential. I may
27:08 ask you that in an exam, that's something important to remember as basics
27:13 we talked about how equilibrium potentials are up by an equal distribution of ions
27:18 can be calculated by knowing the outside inside concentrations of ions. And here
27:24 an example where that equilibrium potentials, one would be much, much different
27:29 the minus 80 or minus 90 value we learned when we talked about the
27:34 potentials at the beginning of this Another thing to note is most of
27:40 information that's coming out of the inner cells. So you can see how
27:45 of these spiral gang neurons are connected inner hair cells and how few of
27:52 are actually connected into the outer hair , guess which ones are more important
27:59 auditor information processing inner hair cells. what is the uh what is the
28:07 of the outer hair cells? If inner hair cells are sending so much
28:11 that information out of the cochlea, what is the function of the outer
28:17 cells and outer hair cells have this cool protein structure built into the positive
28:27 each side and they're like sprays, can they they they go with or
28:34 of a thing, right? So there is a displacement of the plasma
28:40 , those spring like proteins, they stretch and as they stretch, they
28:47 for the amplification of the further displacement the Dior membrane, which promotes the
28:55 of the signal in the inner hair , which is really important that for
29:00 of that auditor information, this is fluoride experiment. We're not going to
29:09 this, but this is really an function of the outer hair sauce is
29:14 sound amplification by amplifying the mechanical displacement the tector membrane by having these springlike
29:29 proteins spring like proteins. OK. talk about the auditory pathway. We
29:37 we learned about the visual pathway, , lateral geniculate nucleus, primary visual
29:45 . And that's where we had the sketch of the outside world. And
29:48 where we ended learning about the visual auditory pathway and the projections are quite
29:57 . They go from the cochleas. have spiral gang cells that will project
30:02 I laterally to the ventral cochlea, dorsal cochlea nuclei from the ventral cochlea
30:11 . The fibers, some of them gonna stay ipsilateral and some of them
30:16 gonna cross over ultra laterally into an known as superior olives from superior.
30:26 of the information is going to travel inferior colliculus. Remember SCP quad gemini
30:33 colliculus, inferior colliculus, superior colliculus sca eye movements, visual system,
30:40 colliculus is processing of the auditory but that is en route before it
30:47 medial geniculate nucleus of the thalamus. it actually gets processed in the brain
30:55 area, auditor information, especially the auditor information. Why would you want
31:01 auditor information so close and then Colliculus severe colliculus, superior colliculus is Syed
31:10 movements, fast eye movements. What we typically react to is visual input
31:17 sound the car is driving by in direction. So there's communication between inferior
31:24 and superior colliculus. So in a , some of this reflexive auditory before
31:30 have full auditory perception, some reflective information and some reflective visual information is
31:37 is being already processed at the level the brain stem brain stem neurons send
31:44 to the outer hair cells. So brainstem neurons will send feedback through the
31:49 gang cells into the outer hair We didn't see that in the visual
31:55 . How from superior colliculus or from G M, we have the feedback
32:00 into the retina but this is different cortex talks to medial geniculate nucleus.
32:07 , reed geniculate nucleus information goes into primary auditory cortex, which is area
32:13 one. And that primary auditory cortex the Lama's corto primary cortex will project
32:22 thalamic inputs. And then from the stem, you can project all the
32:26 back into the cochlea, cochlea nuclei I psy inputs and all others are
32:35 oral. So at the level of brain stem, you already have processing
32:41 these nuclei like superior olive information from ears by oral. Instead of mono
32:51 , this is the tonotopic map and tonotopic map that you have at the
32:56 of the cochlea is preserved spatially and in the frequency like arrangement in the
33:08 ganglion cells in the cochlea nuclei and the way up into the primary auditory
33:19 , which basically these different bands or of cells just like we saw with
33:27 specificity in visual cortex. The cells reacted to certain orientation here in the
33:34 of cells in this area are going be reactive and processing information with highest
33:39 , middle low frequencies. So we this total topic map all the way
33:45 the primary auditory cortex, sound We're not that great at localizing the
33:55 . There are animals in nature that sound much better. But we are
34:01 good. Overall, if we have good hearing, we can tell with
34:05 eyes closed that you know, somebody behind us, some, some cars
34:09 the right of us, maybe some is coming from in front of
34:15 Um When the sound waves are you know, if the sound wave
34:21 coming from the very front here and may reach this area and a little
34:31 later this area and a little bit , this area of your head is
34:36 fraction of the millisecond later we're talking . Uh So it will tell us
34:43 will help us start localizing the And also you will have sound
34:48 So if you're not hearing much in left ear and you're hearing a lot
34:53 your right ear, it's likely that left ear is in the sound shadow
34:57 with the direction of sounds from the . If you're hearing equally, that
35:02 the sound is either from the front the sound shadows in the back or
35:07 the back. And the sound shadow in the front or whatever other orientations
35:13 the sound is coming from the the bottom in different directions. The
35:18 is built in such a way that one of us have different pin,
35:24 know, some of us have big , other of us have small
35:28 Um and they have this funky shape them and the shape is uh built
35:35 such a way that when the sound come into our ears, they are
35:40 to concentrate into the external auditory meatus the auditory canal. So these little
35:48 and things symmetrically, they hop for sound to actually enter into our
35:55 Ok. On an anatomical level, would uh neurons know that the sound
36:03 coming from the left or the Well, we have this arrangement,
36:07 have this tonotopic map and that's for , right. And that's different
36:13 You can have frequency coming from the or frequency coming to the left
36:16 This is not the sound localization map the sound is localized. It's a
36:21 map. But with sound localization, not the situation, the sound from
36:25 left side initiates activity in the left . The sound is coming from the
36:30 , initiates activity, cochlea nucleus activity then sent to the superior olive and
36:35 superior olive. This is an action . It's going to activate neuron,
36:41 super neuron two and neurone three. which one gets activated? First,
36:48 one. OK. So in the , when the sound is now reached
36:54 ear, this ear is in the shadow but a fraction of millisecond later
37:00 milliseconds later, it arrives in my ear. Now, I have sounds
37:04 in the right ear, but it's sometime later, right. The sound
37:10 coming from the left. It hit ear first half a millisecond later,
37:13 coming from here. So it's coming this direction. And by the time
37:19 going to activate neuron three, the from the left is also going to
37:25 neuron three. But before it activated three, it will also activate
37:30 And now this nucleus is gonna know this side was activated first, followed
37:35 this side. Therefore, the sound coming from the left, followed by
37:39 sound coming from the right, if were coming from the front and they
37:45 equally reaching both ears, the two potentials would converge on neuron number
37:52 And that would indicate that the sound coming from the front or the back
37:57 there would be some nuances as So in this case, it's coming
38:02 the left, both impulses reach all our neuron three. At the same
38:05 , the information of synaptic potential generates action potential. Um So this is
38:14 on a anatomical level, you can a tonotopic map and then you can
38:20 which neurons were activated uh based on location or the source of the
38:30 OK. We have a couple of to talk about and then a very
38:35 movie to watch. But let's talk hearing impairments. Most of the time
38:39 you're seeing people that have difficulty they will have hearing aids.
38:46 And hearing aid is typically in older , most of the hearing problems are
38:55 problems and you can have partial loss hearing. Uh and if you have
39:06 problems, it doesn't affect neurons. what are conduction problems, ruptured
39:13 calcified obstacles. Uh this is mechanical problems. They don't conduct the vibrations
39:23 sound or the movement of the fluid well. Disconnection from the oval
39:29 Ok. So these are conduction Sensory neural problems are when you have
39:40 of hair cells. And if you depth of hair cells, you may
39:45 reduced hearing, but in all you may be missing hearing in a
39:50 frequency. An example, the most sensory neural hearing is tinnitus. It's
40:00 called ringing in the ears. Your can ring, you can actually hear
40:06 when your ears are ringing and I hear it, I can hear ringing
40:12 my ears and it is constant. because I went to Chaka Khan concert
40:20 in Houston and stood by the speakers my friends, with my one
40:26 very close to the speakers. When came home, you know, my
40:30 were plugged and I said that's You know, it's like when you
40:34 to a loud play stadium or music , you come back and the following
40:41 you wake up, you know, your ears, you know, you're
40:44 , but I woke up and my were still plugged. So,
40:48 we'll wait. And then a week , they were still clogged up.
40:51 I went to uh check my hearing the clinic and they said you have
40:57 hearing loss in these high frequencies and interesting thing is that the speakers and
41:02 was listening, I turned around and my friends they, they have to
41:06 this high pitch coming from the speakers said it's too loud. Um,
41:10 just her voice but just the way was turned up the, the high
41:14 on the speakers and they said you're these high frequencies, you know,
41:18 I want them to like the Simpsons denial. No, no way.
41:22 know, it can be that, know, I'm gonna come back two
41:26 later, you're gonna test me again then, you know, I'm gonna
41:29 my hearing back. I mean, know, the Doctor said I wouldn't
41:33 that. But if you want to back a month later, we can
41:37 if there's any progress. But in meantime, you have to have,
41:42 know, these uh ear plugs really ones for $150 or something like
41:47 you know. So it came back month later and they're like,
41:52 there's no good news. You, still missing hearing and on top of
41:57 . So what happens is you blow of the hair cells, it actually
42:03 the hair cells and you have this specific anatomy here. Guess what happens
42:09 you kill some of the hair cells the certain frequencies. This this these
42:16 are now gone in a certain area the cochlea and these cells are
42:22 their cell are no longer attached to number. What do you think is
42:28 to the place that is being called here? And now you losses to
42:32 is fluttering around. It's constant movement the moment. And that's what I
42:38 in my ears. And that's what this, this, this ringing,
42:41 high frequency ringing, uh the way cochlea is built and I haven't recovered
42:49 . And sometimes, um, even I don't get enough sleep or uh
42:57 I have my blood pressure go up it's like a torture chamber.
43:04 I never ever been to torture chamber they turn all the high frequency,
43:08 seen movies, you know, like GB torture chambers or whatever else,
43:12 know, bad guys like turning on high frequency pitch, it's constant,
43:17 will drive people literally into, into , into mental state. So and
43:24 , it's kind of a difficult because doesn't go away. So you just
43:27 used to ignoring it. Uh But problem was I like listening to music
43:33 loud and this was just one incident kind of pushed it over the edge
43:39 I haven't recovered my hearing. So have uh a sensory neural loss.
43:47 uh And there are some medications that help steroids, but they don't really
43:53 very well avoiding alcohol and caffeine can sometimes but not really. Um And
44:01 most cases when people have hearing disabilities lack of hearing uh they have hearing
44:11 and hearing aids is like a speaker you place into your ear and it's
44:17 different from cochlear implants. So they're aids or like little speakers you place
44:22 your ear, cochlear implants are right? How are they different?
44:27 implants are quite sophisticated. So you this receiving antenna. So you'll have
44:34 a my microphones, right? And microphones are listening to the sound and
44:40 implanted underneath the skin and they're sending the sound processor. And this is
44:47 receiver circuit for all of the And what is going on is because
44:53 this tonotopic map, you actually implant electrode along the cochlea and many different
45:03 along the cochlea here, but the is also dead. So you're really
45:12 the spiral game songs and you take electrode that you implant inside the
45:21 you wind it around and you program that when the the when the
45:27 when the receiver is hearing a high sound, that high frequency sound is
45:33 stimulate the portion of the electrode that's to high frequencies here. When there
45:40 a sound that's midrange, that's gonna the spiral ganglion cells that would be
45:47 in the area of the cochlea, process middle range and then low frequencies
45:53 be electrodes activating the spiral gang and in that apex and rema where hair
46:00 would build the process, the lowest frequency of sound. So it's very
46:07 . It's, it's cochlear implant is a hearing aid. Uh And it
46:12 a surgical procedure basically of placing an inside the cochlea and having the,
46:19 receiver through the processor convert the frequency sound into specific location for the electrode
46:27 along the cochlea. All right. this uh would pretty much end our
46:36 except that I want to, it into the empty landscape, the noise
46:45 wind and snowfall is filtered out. rustling that the owl is interested in
46:56 false alarm, but it doesn't have wait long from deep under the
47:04 A Leming transmits a high frequency rustle around here, the penalty for wrestling
47:11 death. The signals are too weak our hearing. But this owl has
47:18 ultimate amplifier. Its face acts like satellite dish. The dish is formed
47:26 a ring of stiff feathers. They and channel sound inwards, the eyes
47:35 central, but the dish actually focuses the ears. They are on the
47:40 of the tiny skull. Next, interesting about the ears? This is
47:45 barn owl there, how our ears symmetrical and uh and the hori horizontal
47:55 , their ears are slightly as one is slightly higher and another one
48:00 lower. And that helps with the perception and depth localization of sound because
48:10 , they're not only displaced left and but symmetrically but also up and
48:16 And we talked about when the sound . It allows us to determine where
48:21 coming from and by displacing them in horizontal axis uh or vertically. Uh
48:31 you can have a better uh look depth. The dish is divided by
48:40 line of bristles giving stereo sound. like having a giant cupped hand behind
48:48 ear to pinpoint the lemming, the must tune its receiver. The dish
49:04 moved, the eyes automatically follow too . Then back again, the lemming
49:17 now being totally reckless sound dish and are now focused from this point
49:27 It won't look away until the lemming in its talons. The sorting
49:35 the s approach is absolutely silent, , velvety feathers have serrated edges that
49:49 caress the air as a result. wing flaps interfere with the lemmings
50:02 The head remains focused at all times if it has to fly around
50:09 right? We don't know, we don't know you and you know,
50:20 a carpet of snow, a stationary is easy to hit. Thank
50:29 But it's not just a simple dive attack. The head stays locked on
50:35 the last moment. Then the talents raised into the line of the sound
50:46 on each talon are extended two above two below. Perfect for catching cylindrical
50:55 . The lemmings number is up. if the Leming is moving, the
51:00 can compensate the owl hovers. It signal direction the body twists and the
51:08 are repositioned when you're dealing with this sharp and specialized physical defenses like
51:21 can be useless. The penalty for around here is death. That's my
51:31 phrase from this movie. But, , the fact of the matter is
51:35 those animals can do it at they can do it underneath the
51:42 So it's not that they meet the . A lot of these animals are
51:46 turn off and that's why one of reasons why they also have really good
51:51 localization so that they can hunt at and find their pre thank you so
51:57 and I will see everyone back in class on
-
+