Auditory processing | Processing the Environment | MCAT | Khan Academy


Voiceover: In order to distinguish between the sounds of a base drum and something that has
a much higher frequency, such as the sound of a bee’s wings flapping in the air, your brain is relying on the cochlea, in order to differentiate between the two different sounds. So, the difference between a base drum and a bee’s wings flapping in the air, is the frequency. So a base drum has a very low frequency, whereas the wings of a bee, when they’re moving through
the air very quickly, have a very high frequency. So as the information
from a base drum beating, or a bee’s wings flapping, comes into the ear, they eventually hit the cochlea. And we went into a lot of detail about how exactly the
sound wave is converted into a neural impulse by the cochlea, that eventually reaches the brain. But now we’re gonna go into
how the cochlea distinguishes between sounds of varying frequencies, and how this distinction is maintained all the way to the brain,
in order for the brain to be able to perceive different sounds. So this is known as “Auditory Processing.” Your brain needs to be able to distinguish between sounds of varying frequencies, and you’re actually able to hear things with a frequency of 20 hertz, all the way up to a
frequency of 20,000 hertz. So this is a huge range,
and in order to distinguish between sounds of low
and high frequencies, the brain uses the cochlea, and particularly, something known as “Basilar Tuning.” And the term “basilar” comes from the basilar membrane, which is inside the cochlea. So inside the cochlea,
there’s actually a membrane that contains a bunch of hair cells. And if we were to unroll this cochlea, if we took the cochlea and we unrolled it, so it’s normally rolled up like this, if we unrolled it, so now it’s flat, there are varying hair cells. So this would be the very base, this is the base of the cochlea, and this is the very apex, the very tip. So the base would be right here, the apex would be right here. Now if we unrolled it, and looked at which hair
cells were activated, given different sounds, we would notice that hair
cells at the very base of the cochlea were actually activated by
very high frequency sounds, and hair cells at the
very apex of the cochlea are stimulated by very
low frequency sounds. So let’s look at another picture, just to make things a little bit clearer. So this picture basically just
shows the cochlea unrolled. And as I mentioned before,
this would be the base of the cochlea, I’ll use a darker color. This would be the base of the cochlea, and this would be the
very tip, or the apex of the cochlea. And hair cells are found all
along the basilar membrane, so this membrane right here
is the basilar membrane, and there are hair cells
implanted inside of it, there are a whole bunch
of these hair cells. And hair cells closer to the very base respond to a very high frequency, so this is 1,600 hertz. And hair cells closer to the apex respond to a lower frequency, so 25 hertz. So this would be something
like a base drum, and something with a very high frequency, would be something like a bee’s
wings flapping in the air. So as sounds with varying
frequencies reach the ear, they will stimulate different parts of the basilar membrane. So if we have a base drum being played, it has a pretty low frequency, and it’ll eventually go into
the ear, reach the cochlea, and it’ll actually travel
along this basilar membrane, until it reaches the hair cell that is attuned to that
particular frequency. So let’s say, that this is a frequency
of 100 hertz for example. The sound waves eventually
cause fluid inside the cochlea to travel in such a way, that the hair cells
that are very sensitive to a frequency of 100 hertz, which looks like it’s right around here, will actually activate. And these hair cells will
fire an action potential, and this signal will
eventually reach the brain, and it will be mapped to a very particular part of the brain. So this right here is the brain, and if you lift up this
little piece of brain, there is something known as
the “Primary Auditory Cortex.” And the primary auditory cortex is this blue region over here, and it’s basically
responsible for receiving all of the information from the cochlea. And you can see that
it’s actually separated, similar to how the cochlea separated
to various frequencies, it’s sensitive to various frequencies, this primary auditory
cortex is also sensitive to sounds of various frequencies. So, for example, this would
be a part of the cortex that receives information from hair cells that are sensitive to a
frequency of .5 hertz. And this part of the
auditory cortex receives information from hair
cells that are sensitive to a frequency of 16 hertz. And the reason that this is important, is because the brain needs
to be able to distinguish between various sounds. So if we had all the hair cells sensitive to every single sound, then whenever you heard any sound, then all the hair cells
would fire at once, and they would send this
huge signal to the brain, and the brain wouldn’t
be able to distinguish between different sounds. So by having this basilar tuning, the brain is able to differentiate between sounds with a very high frequency, and sounds with a very low frequency. And this mapping, so this mapping of sounds
with a higher frequency versus sounds of a lower frequency, is known as Tonotypical Mapping.” And just to summarize, we have sounds waves coming into the ear, and different sound waves
have different frequencies. And we need to be able to distinguish between the different frequencies. So the sound waves come in, they hit the cochlea, and they will activate hair cells in different parts of the cochlea. So if it’s a very high frequency sound, it’ll activate a hair cell over here; if it’s a very low frequency sound, it’ll activate a hair cell over here. And these hair cells
will actually send axons, and these axons eventually
all bundle together to form the auditory nerve. And the auditory nerve carries axons from each hair cell inside the cochlea. And the auditory nerve eventually reaches the brain, and will again separate its fibers, and reach different parts of the brain.

Comments 7

  • I am not trying to be a troll honest. My question is as follows: since hair cells are specialized receptor cells wouldn't they fire a receptor potential to release their neurotransmitter rather than an action potential? I am not trying to be a douche tool, honest. I am just confused.

  • Apakah anda benar tuhan the most low is secret id, you in my ear called candy, my mind said cammy

  • Common language more easier interpretation than more high structural like name plc, etc, trus maunya apa, sina

  • i am doing research into things that can cause hearing impairments. One thought is … can an inflamation around the cochlea intermittently disrupt the function of the cochlea.. in varias degrees.. and this inflamtion can effect one or two sides to varying degrees causing the auditory processing to continually be trying to learn / decod correctly what is being said.. causing a pseudoform of hearing loss.. at the same time allowing for "normal" hearing test results which do not tease out the mis decoding of of auditory languange and the complex filtering out of sound.. essentially leving a peron deaf, but with abilityh to hear sound.

  • Nice video, but I believe it is tonotopic, not tono-typical

  • I stopped at 5:24 (future reference)

  • I have auditory processing disorder 😰

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