Hearing: Hair Cells and Semicircular Channels

by Thad Wilson, PhD

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    00:01 How hair cells work? These hair cells are important processes.

    00:08 These hair cells allow for him to be their move from direction or the other.

    00:14 They’re structures is very specific, and have very specific amounts of fluid that they’re filled in.

    00:21 So the endolymph is associated with the top portions of the hair cells.

    00:28 Perilymph is associate with the bottom portion of the cell.

    00:33 What is in special about endolymph, is it's high potassium concentration.

    00:39 It's high potassium concentration is different than other areas in the body where usually have the high potassium concentration inside the cell versus outside the cell.

    00:50 Perilymph is more normal in nature, in which it has a low potassium concentration.

    00:59 So, one of these two different potassium concentrations allow for then the signal process to work.

    01:07 Well, a sound wave is going to be traveling down membrane, pushing on this tectorial membrane that will push down against the hair cells.

    01:17 As it pushes down against the hair cells, the hair cells will deflect.

    01:22 As the hair cells deflect, potassium is allow to rush into those hair cells.

    01:29 Why does potassium wants to rush in? Because the endolymph has such high potassium concentration.

    01:36 There’s a gradient between the endolymph and the cell itself.

    01:41 Membrane potential depolarizes.

    01:44 These opens up calcium channels.

    01:46 These calcium influx causes synaptic vesicles which have glutamate in them to be released.

    01:53 Therefore, these whole processes is set up by potassium entering into the cell to cause depolarization.

    02:00 It is then the release of glutamate that is stimulatory to the next nerve that will transmit the information back to the brain.

    02:09 You might ask, what happens to the potassium? The potassium exits the cell into the perilymph and then is recycled and brought back to the endolymph.

    02:21 Sound Frequency Mapping.

    02:25 So now that you understand how a hair cell works.

    02:28 We can then bring in more information about how you hear different sounds.

    02:33 And different sounds of course have different frequencies, from a high sound to a low sound.

    02:40 These different sounds give you the insight into how a particular wave is coming through.

    02:47 So, you have hair cells allocated from the base all the way to the apex.

    02:54 These will now be responsive to different frequencies.

    02:59 If you have a high frequency sound, this is going to stimulate the membrane closer to the base.

    03:10 This high frequency sound is because of the greater amount of frequency not talking about amplitude here.

    03:17 Frequency, so it's occurring through a large number of frequency waves will hit the hair cells closer to the base.

    03:30 Sounds that are lower frequency have a slower wave.

    03:35 Those who travel in further into the membrane before they will hit a hair cell.

    03:42 That is how you will distinguish between a high pitch and a low pitch, is where the wave comes in to stimulate those particular hair cells associated with the depression in the membrane.

    03:58 So we've discussed sound frequency mapping.

    04:01 But let's add some richness to that information, and that is a particular frequency, although it primarily stimulates a certain area of the tectorial membrane.

    04:12 It will spread a little bit further.

    04:15 So let's take an example of that.

    04:17 If we look at a frequency, let's say 8000 cycles/second.

    04:22 You can see it stimulates a narrow band and if you think about it as the distance from the stay-bees.

    04:29 If you take something like the cycle frequency of 400, you can see it stimulates a much wider area.

    04:38 That wider area of stimulation is going to engage more hair cells, that gives us a little bit more ability to hear different sounds.

    04:49 Besides the sound frequency mapping, the other component that we need to bring out is loudness.

    04:56 For example, when you do a test of hearing, you will do it at different frequencies at the same decibel loudness level.

    05:06 So how do you determine loudness? They usually is how many hair cells you're actually engaging.

    05:13 So you have your outer hair cells that can be stimulated.

    05:17 And if it's a loud enough stimulus, you can also stimulate your inner hair cells.

    05:24 And the more of these hair cells that are engaged, the louder the sound will be perceived in your cerebral cortex.

    About the Lecture

    The lecture Hearing: Hair Cells and Semicircular Channels by Thad Wilson, PhD is from the course Neurophysiology.

    Included Quiz Questions

    1. Endolymph
    2. Perilymph
    3. Hair cell cytosol
    4. Plasma
    1. Oval window
    2. Round window
    3. Apex of the basilar membrane
    4. Apex of the scala tympani
    1. Glutamate
    2. Serotonin
    3. Acetylcholine
    4. GABA
    5. Adrenaline
    1. Calcium
    2. Sodium
    3. Chloride
    4. Magnesium
    5. Potassium

    Author of lecture Hearing: Hair Cells and Semicircular Channels

     Thad Wilson, PhD

    Thad Wilson, PhD

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