Hearing: Hair Cells and Semicircular Channels

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

00:08 These hair cells allow for him to be there 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 its high potassium concentration.

00:39 Its 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.

00:51 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 travelling 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.

01:30 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. 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.

02:01 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.

02:22 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 is so its 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.

03:43 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.