WEBVTT 00:00.000 --> 00:30.000 position:50% align:top line:0% *This machine-generated transcript may have errors. If remediation or a manually-generated transcript is needed, please contact NLM Support at https://support.nlm.nih.gov.* 00:23.120 --> 00:25.550 The human ear is a complex and wonderful 00:25.550 --> 00:28.510 instrument to say though that all it does is 00:28.510 --> 00:31.370 to enable us to hear is to really understate the things 00:31.370 --> 00:32.500 that is capable of. 00:34.640 --> 00:35.990 It is first of all, 00:35.990 --> 00:37.710 a collector of sound waves, 00:38.230 --> 00:40.990 it catches the sound waves and directs them down into the 00:40.990 --> 00:43.860 external canal so that they can find their way on 00:43.860 --> 00:46.380 further into the inner ear where they can be received and 00:46.380 --> 00:46.950 interpreted. 00:48.220 --> 00:51.140 It is also an energy transducer that is, 00:51.140 --> 00:53.580 it changes the acoustic energy of the airborne 00:53.580 --> 00:56.080 signal to mechanical energy to 00:56.080 --> 00:59.020 hydraulic energy and finally to electrical energy. 00:59.970 --> 01:02.850 It is also a sound amplifier that 01:02.850 --> 01:03.030 is, 01:03.030 --> 01:05.670 it actually increases the loudness of the sound 01:05.750 --> 01:07.350 after it reaches the ear. 01:08.120 --> 01:11.120 It's also a sound analyzer that is, 01:11.120 --> 01:13.910 it allows us to be able to interpret the 01:13.910 --> 01:16.190 complex noise that we call speech. 01:16.760 --> 01:17.840 And finally, 01:17.880 --> 01:20.430 it contains the mechanism that 01:20.440 --> 01:23.230 enables us to be able to maintain our balance 01:23.240 --> 01:25.330 and to stay in an upright position. 01:26.070 --> 01:26.210 Now, 01:26.210 --> 01:28.610 I'd like to tell you some things about the ear. 01:28.620 --> 01:30.160 But before we do that, 01:30.200 --> 01:33.180 I'd like to review with you some of the basic notions 01:33.190 --> 01:34.610 of sound and sound. 01:34.610 --> 01:35.140 Waves, 01:35.150 --> 01:37.870 how they're generated where they come from 01:37.880 --> 01:39.690 and how they travel through the air 01:40.980 --> 01:43.420 sound sources can be of varying kinds. 01:43.980 --> 01:46.170 Some examples are the reed of the clarinet, 01:46.480 --> 01:47.060 the bell, 01:47.590 --> 01:49.500 the human voice and a tuning fork. 01:49.730 --> 01:52.370 All of them produce sound in the same basic 01:52.370 --> 01:52.920 way. 01:53.870 --> 01:56.820 Let's review then the four essentials that we need for a sound to be 01:56.820 --> 01:58.080 created and to be heard. 01:58.900 --> 01:59.460 First of all, 01:59.460 --> 02:01.640 we need a vibrator such as a tuning fork. 02:02.310 --> 02:02.930 Secondly, 02:02.930 --> 02:05.480 we need some force to set the vibrator in motion. 02:06.400 --> 02:06.870 Thirdly, 02:06.870 --> 02:09.640 we need a medium such as the air to convey the 02:09.640 --> 02:11.670 wave motion created by the vibrator. 02:12.440 --> 02:13.110 And finally, 02:13.110 --> 02:16.000 we need the hearing mechanism itself which can receive 02:16.000 --> 02:17.200 and interpret the sound. 02:18.410 --> 02:21.290 I think the best example to explain how a sound 02:21.290 --> 02:23.420 wave is generated is the tuning fork. 02:24.380 --> 02:27.350 If you were to squeeze the tides of the tuning fork together 02:27.360 --> 02:28.890 and then let them snap apart, 02:29.360 --> 02:31.530 you would of course generate a pure tone. 02:32.260 --> 02:35.120 The reason why the tone is generated is 02:35.120 --> 02:37.770 because as the time springs back 02:37.780 --> 02:39.880 past its original resting position, 02:40.710 --> 02:43.330 it pushes the molecules of the air together and 02:43.340 --> 02:44.990 causes them to bunch up, 02:45.300 --> 02:46.490 it condenses them. 02:47.080 --> 02:48.660 Then as it springs back again, 02:48.660 --> 02:49.930 in the opposite direction, 02:49.940 --> 02:52.860 it creates a vacuum or a rare faction 02:52.920 --> 02:55.720 where there are fewer molecules than there should be. 02:56.260 --> 02:59.060 This constant repetition of condensation 02:59.070 --> 03:02.060 and rare faction increase in pressure, 03:02.110 --> 03:04.770 decrease in pressure is the basis for the sound 03:04.770 --> 03:05.280 wave. 03:06.030 --> 03:06.300 Now, 03:06.300 --> 03:09.200 it's important to remember that it's not the molecules in 03:09.200 --> 03:10.800 the air themselves that travel. 03:11.120 --> 03:13.790 But rather the pressure changes that travel through the 03:13.790 --> 03:15.040 air to the ear. 03:17.280 --> 03:20.110 There are two basic characteristics of a sound wave that I 03:20.110 --> 03:21.920 think you should be familiar with. 03:22.090 --> 03:23.490 The first is frequency, 03:24.290 --> 03:26.880 frequency is analogous to pitch. 03:27.840 --> 03:30.510 And it's defined as being the 03:30.510 --> 03:32.740 number of times the 03:32.750 --> 03:35.500 repetition of condensation and 03:35.500 --> 03:38.280 rare faction occurs in some unit time. 03:38.290 --> 03:39.070 For example, 03:39.070 --> 03:40.260 in 1 2nd, 03:42.320 --> 03:44.880 the fewer number of times in a second 03:45.130 --> 03:47.680 that the conversation and rare faction cycle 03:47.870 --> 03:48.640 goes on. 03:48.650 --> 03:50.040 Then the lower the pitch, 03:51.040 --> 03:53.890 the greater the number of times that this condensation 03:53.890 --> 03:55.970 rare faction cycle goes on. 03:56.140 --> 03:58.190 Then the higher the perceived pitch, 03:58.950 --> 04:00.540 if you will look at the screen, 04:00.540 --> 04:03.160 you will be able to see a representation of 04:03.540 --> 04:06.150 a pure tone that's been created by an 04:06.150 --> 04:07.200 oscilloscope. 04:14.420 --> 04:16.930 The uppermost portion of the sound wave is that 04:17.180 --> 04:19.670 represents the condensation portion. 04:19.700 --> 04:22.480 The lower most portion represents the rare 04:22.480 --> 04:23.600 faction portion. 04:24.140 --> 04:26.980 You can see that these waves are some 04:26.980 --> 04:29.360 distance apart and probably 04:29.360 --> 04:32.300 represent a tone with a frequency of about 04:32.310 --> 04:34.960 250 cycles per second 04:34.970 --> 04:37.540 as we increase the tone so that the 04:37.540 --> 04:39.730 frequency is close to 1000 cycles per 04:39.730 --> 04:40.690 second, 04:40.700 --> 04:42.720 the waves come closer together. 04:42.740 --> 04:45.390 And we see more a greater number of 04:45.390 --> 04:48.090 repetitions of condensation and rare faction. 04:48.160 --> 04:49.190 In a second. 04:50.300 --> 04:53.260 The other aspect of a sound wave that I would want you to be 04:53.260 --> 04:54.780 familiar with is amplitude. 04:55.430 --> 04:58.300 Amplitude simply relates to the fact that 04:58.310 --> 05:01.210 the strength of the particle or molecular energy 05:01.210 --> 05:01.990 is greater. 05:02.000 --> 05:04.050 And so we have a louder sound. 05:04.690 --> 05:07.400 This is represented on the screen by the 05:07.400 --> 05:10.250 sound wave increasing in amplitude, 05:10.360 --> 05:13.190 you can see that the envelope becomes wider as the sound 05:13.190 --> 05:14.100 becomes louder. 05:14.860 --> 05:16.720 Then as the sound becomes softer, 05:17.080 --> 05:19.550 the envelope of the sound wave decreases and 05:19.550 --> 05:20.750 becomes smaller. 05:22.680 --> 05:23.000 Now, 05:23.000 --> 05:23.900 this example, 05:23.900 --> 05:26.800 from the tuning fork is a fairly simple 05:26.810 --> 05:29.450 representation of a sound wave and it's 05:29.450 --> 05:32.030 normally not one that we run into every day. 05:32.950 --> 05:35.890 I better a different example which I would like 05:35.900 --> 05:38.530 to show you is what the human voice would look 05:38.530 --> 05:41.060 like if you were to put it on a 05:41.060 --> 05:43.640 screen as I'm talking. 05:43.640 --> 05:43.920 Now, 05:43.920 --> 05:46.510 you can see the jumble of lines and angles on the 05:46.510 --> 05:49.430 screen representing my voice as it comes 05:49.430 --> 05:49.980 to you. 05:50.840 --> 05:51.190 It's, 05:51.200 --> 05:54.090 it's really a wonderful thing to consider the human ear that it 05:54.090 --> 05:57.090 can take such a jumble of noise and 05:57.090 --> 05:58.040 make sense out of it. 05:58.730 --> 05:59.040 Now, 05:59.040 --> 06:01.980 let's take a look at the year just how it's made and just 06:01.980 --> 06:02.780 how it works. 06:03.240 --> 06:06.160 The year is first of all located in the petrus 06:06.160 --> 06:09.080 portion of the temporal bone and this is 06:09.080 --> 06:12.040 the hardest bone in the body and nature designed 06:12.040 --> 06:14.300 it that way to be sure and protect the inner ear from 06:14.300 --> 06:15.050 damage. 06:16.320 --> 06:17.110 As a matter of fact, 06:17.110 --> 06:19.690 the word petrus derives from the Latin word 06:19.690 --> 06:20.170 petrus, 06:20.170 --> 06:21.300 which means rock, 06:22.210 --> 06:25.050 the outer ear is connected to the skull by a 06:25.050 --> 06:27.870 series of muscles ligaments and other 06:27.870 --> 06:28.440 tissue. 06:28.950 --> 06:29.100 Now, 06:29.100 --> 06:31.670 most of the muscles that attach the outer 06:31.670 --> 06:34.300 ear to the skull 06:34.470 --> 06:35.930 are vestigial. 06:36.010 --> 06:37.090 That is at one time, 06:37.090 --> 06:39.980 we used to use them the same way an animal uses 06:39.980 --> 06:42.480 them now to turn his ears to localize 06:42.480 --> 06:43.120 sound. 06:43.330 --> 06:46.330 But uh they are no longer of any 06:46.330 --> 06:48.240 real use to us at this time. 06:49.870 --> 06:52.690 The outer ear is the first thing that 06:52.690 --> 06:54.000 receives the sound. 06:54.710 --> 06:57.340 It's ovoid in shape and contains a 06:57.340 --> 06:59.950 number of depressions and humps. 07:00.030 --> 07:02.640 Its function is to collect the 07:02.640 --> 07:05.270 sound waves as they hit it and direct them 07:05.270 --> 07:07.790 down and into the external canal. 07:13.080 --> 07:15.910 It provides us with about 10 decib of 07:15.910 --> 07:16.990 amplification. 07:17.100 --> 07:17.300 Now, 07:17.300 --> 07:19.580 this amount of amplification is really not 07:19.580 --> 07:20.430 significant. 07:20.820 --> 07:21.840 As a matter of fact, 07:21.840 --> 07:23.790 if we were to lose the outer ear, 07:24.130 --> 07:26.910 it would not cause any real loss of 07:26.910 --> 07:27.880 hearing for us. 07:28.190 --> 07:31.100 So even the outer ear itself is not that useful 07:31.100 --> 07:33.510 to us today and serves primarily a 07:33.510 --> 07:34.770 cosmetic function. 07:36.440 --> 07:36.700 Now, 07:36.700 --> 07:39.430 as we move from the outer ear 07:39.430 --> 07:41.010 into the external canal, 07:41.140 --> 07:44.020 remember now that the sound waves coming through 07:44.020 --> 07:46.890 the air are collected by the outer ear 07:46.900 --> 07:49.800 and directed down into the canal where they 07:49.800 --> 07:51.940 finally will hit the ear drum. 07:53.930 --> 07:56.860 The external canal is about an inch long and 07:56.860 --> 07:59.850 it's about a quarter to a half inch in diameter. 08:01.010 --> 08:03.920 The tissue that uh is made that makes 08:03.920 --> 08:06.670 up the wall of the external canal is the same 08:06.670 --> 08:09.540 tissue that is connected with the tissue 08:09.550 --> 08:12.500 that makes that up that tissue of the ear, 08:12.540 --> 08:13.340 the hand, 08:13.370 --> 08:14.840 the back and so forth. 08:15.680 --> 08:18.560 There are two things about the external canal that I think you should be 08:18.560 --> 08:19.400 familiar with. 08:20.280 --> 08:22.970 One is that it contains a number of hairs 08:22.980 --> 08:24.710 along this portion here. 08:26.030 --> 08:28.820 And the function of those hairs is to protect it 08:28.820 --> 08:31.320 from insects intruding into the external 08:31.320 --> 08:32.200 canal. 08:32.360 --> 08:33.490 In addition to that, 08:33.490 --> 08:34.810 there are also in here, 08:34.820 --> 08:37.310 a number of glands which are called saruman. 08:37.310 --> 08:39.680 It's glands and they will 08:39.850 --> 08:42.650 produce saruman or what's more 08:42.650 --> 08:44.970 popularly known as earwax. 08:45.470 --> 08:45.630 Now, 08:45.630 --> 08:48.210 this earwax or saruman is very bitter 08:48.210 --> 08:50.450 tasting and repugnant material. 08:50.540 --> 08:53.480 And it also serves the function of protecting the 08:53.480 --> 08:56.100 ear from the intrusion of insects. 08:57.690 --> 08:58.080 Now, 08:58.090 --> 09:00.950 the sound wave comes down 09:00.960 --> 09:03.910 from the article into the external 09:03.910 --> 09:05.140 canal and finally, 09:05.150 --> 09:07.430 it comes up to the middle ear, 09:08.260 --> 09:10.740 the middle ear is made up of the ear 09:10.740 --> 09:11.310 drum, 09:12.470 --> 09:15.090 The articular chain which is made up of three 09:15.090 --> 09:16.320 tiny bones called the, 09:16.710 --> 09:17.050 asse. 09:17.800 --> 09:20.580 the Incas and the stay 09:20.580 --> 09:21.120 peas. 09:25.010 --> 09:27.640 The function of the middle ear 09:27.650 --> 09:30.070 is to transform the 09:30.070 --> 09:32.590 acoustic energy into mechanical 09:32.590 --> 09:35.450 energy and also to increase or 09:35.450 --> 09:38.340 amplify the amount of sound that that 09:38.350 --> 09:39.560 is reaching the ear. 09:40.250 --> 09:43.000 And it does this by means of what is 09:43.000 --> 09:45.830 called the a real ratio. 09:45.900 --> 09:48.570 That is if we take the ratio of 09:48.570 --> 09:51.080 the area of the Eardrum to the 09:51.080 --> 09:53.280 ratio of the area of this foot plate. 09:53.280 --> 09:54.050 Here, 09:54.110 --> 09:57.110 we find that the increase in sound is 09:57.110 --> 09:58.790 about 18 times. 09:59.600 --> 10:00.060 Now, 10:00.260 --> 10:03.130 it's necessary for this to occur because 10:03.380 --> 10:04.750 the sound after it leaves, 10:04.750 --> 10:06.710 the middle ear will go into the inner ear, 10:06.710 --> 10:07.920 which is filled with fluid. 10:08.880 --> 10:11.880 And it's necessary to overcome the impedance which 10:11.880 --> 10:13.870 is offered by the fluid, 10:14.040 --> 10:16.200 the fluid in the inner ear. 10:22.040 --> 10:24.730 There are two muscles in the middle ear, 10:24.790 --> 10:26.970 which we should be familiar with. 10:27.070 --> 10:29.400 And those are called the tensor tympani. 10:29.560 --> 10:31.110 And the step PDS muscle, 10:31.260 --> 10:34.220 the tensor tympani originates here and comes 10:34.220 --> 10:37.140 across the middle ear space to the handle of 10:37.140 --> 10:37.940 the malas. 10:38.630 --> 10:41.080 The step pds muscle originates on the 10:41.080 --> 10:43.590 posterior wall behind these bones 10:43.840 --> 10:46.710 and it inserts right here in the head of the stay peas. 10:47.430 --> 10:50.230 These two muscles serve a protective function 10:50.840 --> 10:53.820 that is whenever a sound which is loud enough to 10:53.820 --> 10:56.080 cause damage to the ear occurs, 10:56.090 --> 10:58.880 they contract very quickly and they 10:58.880 --> 11:01.810 pull the articular 11:01.810 --> 11:03.960 chain off its normal course of action. 11:03.970 --> 11:06.870 And so it protects the inner ear from uh 11:06.880 --> 11:07.820 from damage. 11:09.020 --> 11:09.200 Now, 11:09.200 --> 11:12.180 when the sound wave it comes 11:12.180 --> 11:14.800 down into the external canal and it hits the 11:14.800 --> 11:15.300 eardrum, 11:16.210 --> 11:18.650 it causes the eardrum to vibrate at the same 11:18.650 --> 11:21.590 frequency and amplitude as the sound as the 11:21.590 --> 11:22.540 original sound. 11:23.800 --> 11:26.350 The articular chain is connected to the eardrum. 11:26.350 --> 11:29.180 And so that also vibrates at the 11:29.180 --> 11:31.070 same frequency and amplitude. 11:31.550 --> 11:34.320 And so the sound wave is now conducted across this 11:34.320 --> 11:37.080 middle ear space up to the inner 11:37.080 --> 11:39.970 ear as as of yet 11:39.970 --> 11:40.700 though no, 11:40.710 --> 11:42.590 no hearing has taken place. 11:42.600 --> 11:45.390 The only thing that's really happened is that the sound 11:45.390 --> 11:48.150 wave has been conducted up to the inner 11:48.150 --> 11:48.650 ear. 11:50.280 --> 11:53.050 The other part of the inner ear that you should be familiar 11:53.050 --> 11:55.630 with is something called the U station 11:55.630 --> 11:56.640 tube. 11:56.670 --> 11:58.730 And this is located in the 11:58.730 --> 12:01.460 anterior inferior portion 12:01.480 --> 12:02.980 of the middle ear space. 12:04.060 --> 12:06.850 The station tube runs from the middle 12:06.850 --> 12:09.270 airspace down to the nasal firing. 12:09.270 --> 12:11.880 So to the back of your throat And it 12:11.880 --> 12:13.860 serves two functions. 12:14.290 --> 12:15.220 First of all, 12:15.230 --> 12:18.100 it provides a constant source of oxygen 12:19.060 --> 12:20.450 to the middle ear space. 12:21.540 --> 12:24.310 The second thing it does is to is to provide an 12:24.320 --> 12:26.800 equalization of pressure whenever there are 12:26.800 --> 12:28.260 changes in altitude. 12:29.000 --> 12:31.770 If you were to experience a 12:31.770 --> 12:33.250 severe change in altitude, 12:33.250 --> 12:34.030 for example, 12:34.870 --> 12:37.680 the pressure on the outside of your ear 12:37.880 --> 12:39.630 would be less than the pressure on your, 12:39.700 --> 12:40.940 on the inside of your ear. 12:40.940 --> 12:42.770 And it would force the ear drum outward. 12:43.640 --> 12:44.630 If you yawn, 12:46.230 --> 12:49.210 then you open the station tube and it allows the air 12:49.210 --> 12:50.540 to come up into the middle ear. 12:50.540 --> 12:52.480 And so it equalizes this pressure. 12:52.950 --> 12:54.710 I'm sure if you've flown in an airplane, 12:54.710 --> 12:57.700 you have probably experienced this and have had 12:57.700 --> 13:00.120 to equalize that pressure in order to get rid of the 13:00.130 --> 13:02.960 uncomfortable or stuffy feeling that you find in your 13:02.960 --> 13:03.420 ear. 13:12.880 --> 13:13.550 Now, 13:15.460 --> 13:16.980 once the sound wave again, 13:16.980 --> 13:18.870 has crossed the middle ear, 13:20.200 --> 13:22.430 it enters the inner ear 13:23.240 --> 13:26.180 it is in the inner ear that the essential organ of 13:26.180 --> 13:27.610 hearing is contained. 13:28.630 --> 13:31.610 The inner ear contains also the balance 13:31.610 --> 13:32.310 mechanism. 13:32.730 --> 13:35.180 And this mechanism is made up of the three 13:35.180 --> 13:36.800 semicircular canals, 13:37.590 --> 13:39.600 the sack you'll and the you trickle. 13:40.040 --> 13:41.630 And this mechanism, 13:41.640 --> 13:44.640 all of these parts working together provide 13:44.640 --> 13:47.550 us with a sense of balance to keep ourselves upright. 13:48.860 --> 13:51.500 This yellow line that you see here is the 13:51.500 --> 13:54.120 vestibular portion of the auditory nerve. 13:56.600 --> 13:59.390 The other portion of the inner ear or the labyrinth is 13:59.390 --> 14:00.890 called the cochlea. 14:01.340 --> 14:04.180 And this is a spiral or snail shaped 14:04.180 --> 14:06.860 bony labyrinth within which the 14:06.860 --> 14:09.050 essential organ of hearing is located. 14:13.180 --> 14:15.330 This portion of the inner ear is called the 14:15.360 --> 14:16.370 vestibule. 14:17.050 --> 14:19.620 And you can see that there are three channels here. 14:20.300 --> 14:23.250 This is the scale of vestibular or the 14:23.250 --> 14:24.620 vestibular channel. 14:24.720 --> 14:27.660 The scallop media or the middle channel and the 14:27.660 --> 14:30.440 skeleton pony or the tim panic channel. 14:31.950 --> 14:34.700 This area in here is filled with a fluid 14:34.710 --> 14:36.120 which is called parallel. 14:37.210 --> 14:40.170 And this middle channel floats 14:40.170 --> 14:43.020 in that parallel and it protects it from 14:43.030 --> 14:45.390 bumping up against the walls of the bony 14:45.400 --> 14:47.020 uh capsule. 14:47.600 --> 14:49.970 The fluid which is inside the scallop 14:49.970 --> 14:52.010 media is called indolent. 14:52.100 --> 14:54.150 And this is much different than the parallel 14:54.610 --> 14:57.450 and arises from somewhere near the cortex. 15:03.660 --> 15:04.150 Now, 15:04.160 --> 15:04.730 when, 15:04.890 --> 15:05.960 when we hear 15:07.250 --> 15:09.540 the acoustic signal, 15:09.540 --> 15:11.860 which has been changed to uh mechanical 15:11.860 --> 15:14.640 energy now has to come into the inner 15:14.640 --> 15:17.180 ear and be somehow changed into hydraulic 15:17.180 --> 15:20.030 energy and then into electrical energy. 15:20.710 --> 15:20.950 Now, 15:20.950 --> 15:23.660 what I would like to do is to show you a 15:23.670 --> 15:26.340 more detailed version of what the cochlea 15:26.520 --> 15:28.640 looks like and just what it's made up of. 15:31.540 --> 15:31.690 Now, 15:31.690 --> 15:34.600 this picture over here is a much 15:34.600 --> 15:37.300 more detailed version of the cochlea. 15:38.940 --> 15:39.590 Right here. 15:39.590 --> 15:42.160 We have the auditory branch 15:42.170 --> 15:45.150 of the 8th cranial nerve coming on 15:45.160 --> 15:47.830 up into the cochlea and branching 15:47.830 --> 15:50.060 off at every level. 15:52.030 --> 15:54.930 You can see the snail shaped appearance 15:55.490 --> 15:56.440 of the cochlea. 15:56.440 --> 15:59.200 And this picture shows it as though it had been 15:59.200 --> 16:00.880 cut straight down the middle. 16:02.190 --> 16:04.460 The arrows that you see indicate the 16:04.460 --> 16:07.300 direction uh the force, 16:07.300 --> 16:09.920 the direction of the force of the 16:09.930 --> 16:12.490 energy which is created by the sound wave, 16:12.500 --> 16:15.310 it moves on up and then at the 16:15.310 --> 16:18.150 top turns around comes back down. 16:18.790 --> 16:19.420 Again. 16:21.860 --> 16:21.990 Now, 16:21.990 --> 16:24.820 here's an even more 16:24.820 --> 16:25.650 detailed 16:28.480 --> 16:31.390 picture of of the cochlea. 16:32.600 --> 16:34.870 This is just one section of it. 16:35.300 --> 16:35.760 And again, 16:35.760 --> 16:38.550 you can see a fiber from the eighth cranial 16:38.550 --> 16:41.520 nerve coming on through the spiral lamanna to 16:41.520 --> 16:43.910 connect with the essential organ of hearing. 16:44.040 --> 16:46.130 This is the scalar vestibular, 16:47.090 --> 16:49.760 the scalar tympani and the 16:49.760 --> 16:52.710 scalar media within 16:52.710 --> 16:54.310 the scalar media contains, 16:54.310 --> 16:54.820 as I said, 16:54.820 --> 16:56.490 the essential organ of hearing, 16:57.380 --> 16:59.430 the scalar media is bounded by 16:59.860 --> 17:01.810 prisoners membrane here, 17:02.870 --> 17:05.790 the base layer membrane here 17:06.610 --> 17:08.220 and the spiral ligament 17:09.370 --> 17:09.990 here 17:12.750 --> 17:15.000 within the scalar media, 17:15.490 --> 17:17.970 we find the sectorial 17:17.970 --> 17:18.700 membrane 17:20.400 --> 17:23.000 and the organ of corti, 17:23.080 --> 17:24.210 the pink area 17:25.840 --> 17:27.200 in the organ of corti. 17:27.210 --> 17:29.980 You'll see hair cells 17:29.990 --> 17:32.280 located along its whole length. 17:32.290 --> 17:34.750 Each of these hair cells is connected 17:34.750 --> 17:37.290 to the nerve of hearing 17:42.140 --> 17:43.250 when they say no 17:44.860 --> 17:47.580 comes from the middle ear into the inner ear. 17:48.300 --> 17:50.080 A number of things happen. 17:51.300 --> 17:52.130 First of all, 17:53.810 --> 17:56.500 the stay peas moves inward 17:57.510 --> 17:58.310 as it does, 17:58.320 --> 18:00.830 it compresses the fluid in the inner ear. 18:01.740 --> 18:04.540 Now that pressure has to be released somewhere. 18:05.650 --> 18:08.530 And right down here in the skeleton pony is something called a 18:08.530 --> 18:09.680 round window. 18:11.390 --> 18:14.080 The staples moves in through the over window, 18:14.920 --> 18:15.650 compresses. 18:15.650 --> 18:17.760 The fluid causes it to move. 18:17.770 --> 18:20.620 That pressure is released at the 18:20.630 --> 18:22.420 round window. 18:25.180 --> 18:27.130 So the signal again comes 18:28.180 --> 18:31.010 by way of the article to the external canal. 18:31.330 --> 18:34.290 It has changed to mechanical energy and 18:34.290 --> 18:36.910 amplified across the time panic membrane of 18:36.910 --> 18:38.370 secular change structure. 18:38.610 --> 18:41.560 And now it is causing the fluid of the inner ear 18:41.880 --> 18:42.690 to move. 18:42.690 --> 18:45.620 And so now it has been changed into hydraulic 18:45.620 --> 18:46.220 energy. 18:50.770 --> 18:52.660 You can see the dotted lines here 18:53.710 --> 18:56.600 and they indicate that as that fluid 18:56.610 --> 18:59.010 is moving through the inner ear, 19:00.070 --> 19:02.620 it causes this membrane to bulge 19:02.630 --> 19:03.160 inward. 19:04.650 --> 19:07.590 That membrane causes the fluid in here to 19:07.590 --> 19:08.200 move. 19:09.820 --> 19:12.760 That in turn causes the tech tutorial membrane to 19:12.760 --> 19:13.830 bend downward. 19:14.550 --> 19:17.240 And now you see the hair cells here which are connected 19:17.240 --> 19:19.940 between the organ of corti and the tech 19:19.940 --> 19:20.870 tutorial membrane. 19:21.280 --> 19:23.730 When the tech tutorial membrane bends downward, 19:24.480 --> 19:27.220 it distorts or bends these hair 19:27.220 --> 19:29.760 cells out of shape as soon as it does 19:29.760 --> 19:30.510 that, 19:30.630 --> 19:33.260 that triggers off an electrical 19:33.360 --> 19:34.040 signal, 19:34.760 --> 19:37.650 Which is then picked up by the fibers 19:37.650 --> 19:40.620 of the 8th cranial nerve and 19:40.620 --> 19:43.550 carried on up through the central nervous system to 19:43.550 --> 19:44.340 the cortex. 19:45.670 --> 19:46.880 The movement of the fluid, 19:46.890 --> 19:47.480 of course, 19:47.640 --> 19:50.560 being pressure continues on. 19:50.560 --> 19:53.170 And you can see the basilar membrane has 19:53.170 --> 19:54.500 bent down also 19:55.560 --> 19:58.430 that causes this fluid to continue 19:58.430 --> 19:58.930 moving. 20:00.130 --> 20:02.390 And if we can go back over here again for a minute, 20:03.620 --> 20:06.170 it would be released here at the oval 20:06.170 --> 20:06.710 window. 20:09.000 --> 20:10.210 Let's take a look at 20:12.280 --> 20:15.200 schema ties version of 20:15.200 --> 20:16.500 the inner ear. 20:17.400 --> 20:20.220 Remember the inner ear is coiled 20:20.230 --> 20:22.630 snail shaped of 2.5 turns. 20:24.390 --> 20:27.090 And so we've schema ties it a little bit here in order to 20:27.090 --> 20:28.870 show you in some detail, 20:28.870 --> 20:30.070 just how it works. 20:32.060 --> 20:34.950 The sound comes down through the the external 20:34.950 --> 20:37.500 canal hits the 20:37.500 --> 20:40.390 eardrum that is connected to the articular 20:40.390 --> 20:40.900 chain. 20:41.620 --> 20:42.730 Now, 20:42.840 --> 20:45.310 the foot plate of the stay peas moves into 20:45.310 --> 20:48.270 the the vestibule and 20:48.270 --> 20:50.350 it compresses this fluid in here. 20:51.920 --> 20:52.440 Now, 20:53.580 --> 20:55.930 you can see that at this point, 20:57.210 --> 21:00.200 this continuation or movement of fluid 21:00.200 --> 21:02.690 through the inner ears taking place, 21:03.340 --> 21:05.590 risers membrane is bending downward. 21:05.600 --> 21:07.470 The fluid continues to compress 21:08.320 --> 21:10.900 it causes the basal membrane to bend 21:11.030 --> 21:13.760 and comes right on down through and finds its release 21:13.760 --> 21:16.590 here at the round window. 21:17.770 --> 21:19.750 These arrows here indicate 21:19.840 --> 21:22.620 the pressure which is not 21:22.650 --> 21:24.810 necessary here or not, 21:24.820 --> 21:27.510 uh which is not necessary at this 21:27.510 --> 21:30.400 point going on up around through the 21:30.400 --> 21:33.400 whole system and eventually coming out through the round 21:33.400 --> 21:33.830 window. 21:39.220 --> 21:41.990 The basil er end of the 21:42.000 --> 21:44.260 inner ear contains those 21:44.270 --> 21:47.070 uh hair cells and fibers 21:47.080 --> 21:49.340 which are responsible for low pitched 21:49.340 --> 21:50.110 sounds. 21:50.210 --> 21:52.340 I beg your pardon for high pitched sounds. 21:52.910 --> 21:55.890 The a pickle end up here is responsible 21:55.890 --> 21:58.550 for those uh hair cells and 21:58.550 --> 22:01.350 fibers which are responsible for low 22:01.350 --> 22:02.440 pitched sounds. 22:04.240 --> 22:06.520 Once the the 22:07.060 --> 22:09.910 hair cells have been excited and trigger off this 22:09.910 --> 22:11.300 electrical response, 22:11.340 --> 22:14.180 they will excite the fibers of the eighth 22:14.180 --> 22:16.710 cranial nerve And they all come 22:16.710 --> 22:19.210 together in a bunch 22:19.220 --> 22:19.730 of, 22:19.740 --> 22:20.730 of nerve fibers, 22:20.730 --> 22:23.340 which is called the spiral ganglion. 22:23.360 --> 22:26.340 And then they find their way on up through the 22:26.340 --> 22:29.060 central nervous system to the cortex where the 22:29.060 --> 22:30.810 sound is interpreted. 22:31.850 --> 22:32.060 Now, 22:32.060 --> 22:34.840 what we've been discussing so far is the way we hear 22:34.840 --> 22:36.740 by what is called air conduction. 22:37.390 --> 22:40.160 That is the signal travels from the air 22:40.170 --> 22:42.760 directly into the ear canal into the inner 22:42.760 --> 22:43.220 ear. 22:43.840 --> 22:46.610 This is the way that we normally hear in most everyday 22:46.610 --> 22:47.440 situations. 22:48.000 --> 22:50.950 There is another way though that we can hear and it's called hearing by 22:50.950 --> 22:51.870 bone conduction. 22:52.440 --> 22:52.610 Now, 22:52.610 --> 22:55.130 if we can take a look at this chart, 22:55.130 --> 22:55.620 again, 22:57.470 --> 22:59.930 recall that the inner ear is 22:59.930 --> 23:02.800 encased in a capsule of bone and that bone is 23:02.800 --> 23:03.800 part of the skull. 23:04.760 --> 23:07.730 When a sound wave is strong enough to cause the 23:07.730 --> 23:09.530 bones of the skull to vibrate, 23:10.750 --> 23:13.140 those vibrations can cause the 23:13.140 --> 23:15.180 fluid in the inner ear to 23:15.180 --> 23:18.130 move and to carry out the 23:18.130 --> 23:20.910 same essential process as 23:20.920 --> 23:22.830 happens by air conduction. 23:24.200 --> 23:24.390 Now, 23:24.390 --> 23:27.200 this is normally not important for us as long as 23:27.200 --> 23:29.850 the outer ear and the middle ear are intact. 23:30.650 --> 23:32.590 But for those persons who have some 23:32.810 --> 23:35.810 pathology of the outer and middle ear, 23:35.820 --> 23:38.080 who may perhaps need a hearing aid, 23:38.450 --> 23:40.730 we can provide a hearing aid that would put a 23:40.730 --> 23:43.630 vibrator right here on the skull and 23:43.630 --> 23:46.270 that would cause the bones of the skull to vibrate 23:46.790 --> 23:48.870 at an in an amplified way, 23:49.020 --> 23:50.500 excite the inner ear. 23:50.600 --> 23:52.800 And so allow him to be able to hear 23:52.940 --> 23:53.780 normally. 23:55.380 --> 23:55.540 Now, 23:55.540 --> 23:58.410 let's just take a look again at the 23:58.410 --> 24:01.090 whole process of hearing by air conduction. 24:02.340 --> 24:05.300 Remember that we have a signal which is generated, 24:05.310 --> 24:05.930 for example, 24:05.930 --> 24:08.140 by a tuning fork, 24:09.650 --> 24:12.640 it generates a number of compensations and 24:12.640 --> 24:15.150 rare factions changes in 24:15.150 --> 24:15.870 pressure. 24:16.200 --> 24:18.940 Those pressure changes find their way through the 24:18.940 --> 24:21.720 air are collected by the external 24:21.720 --> 24:24.370 ear and forced down into the ear canal. 24:25.600 --> 24:28.560 They reached the eardrum secular 24:28.560 --> 24:31.430 change structure where they are changed to mechanical 24:31.430 --> 24:32.680 energy and amplified. 24:35.230 --> 24:38.020 They then find their way into the inner ear when the 24:38.020 --> 24:40.790 foot plate of the staples moves in and out in 24:40.790 --> 24:43.130 time to the signal that came into the year 24:43.130 --> 24:43.810 originally. 24:44.200 --> 24:46.410 And that causes the fluid to move, 24:46.970 --> 24:49.640 causes the membrane structure to move. 24:49.640 --> 24:52.640 And so excites the nerves of hearing from 24:52.640 --> 24:52.890 there. 24:52.890 --> 24:55.680 They then find their way on up through the central nervous system 24:55.830 --> 24:58.190 to the cortex where they're received 24:58.200 --> 24:59.580 analyzed and interpreted. 25:01.660 --> 25:01.820 Now, 25:01.820 --> 25:03.910 that's essentially how the ear works. 25:05.730 --> 25:08.700 Uh it's come a long way since the time when it 25:08.700 --> 25:11.210 was a simple system for that in a 25:11.210 --> 25:13.640 fish millions of years ago. 25:13.640 --> 25:16.580 So that the fish could detect the pressure changes in the 25:16.580 --> 25:19.130 water and maintain an upright and balanced 25:19.130 --> 25:19.760 position. 25:20.490 --> 25:23.430 We've learned a lot about it since the early days of, 25:23.440 --> 25:24.600 since 1950, 25:24.600 --> 25:24.810 with, 25:24.820 --> 25:27.110 with the invention of the electron microscope, 25:27.140 --> 25:29.830 but we still have a lot more to learn and I'm 25:29.830 --> 25:31.860 sure that in the next few years we'll, 25:31.950 --> 25:34.690 we'll see a lot more being added to our store of knowledge 25:34.690 --> 25:36.820 about the year and how we hear.