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Current time:0:00Total duration:11:27

Video transcript

in this video we're going to talk about our sense of sound our sense of sound is also known as audition so in order is in order for us to hear anything two things have to happen first there has to be some sort of stimulus and in the case of sound that stimulus is something known as a sound wave so a pressurised sound wave so that's the first thing that needs to be present in order for us to hear anything the second thing aside from the stimulus is some sort of receptor that's sensitive to the stimulus and in the case of audition that receptor is is something known as a hair cell and the hair cell is a specialized receptor that's bound within the cochlea and we'll discuss this in further detail later in the video so let's take a look at these two things so what exactly is a pressurized sound wave let's let's look at an example so whenever you clap your hands you have learned from experience that people when they clap their hands it makes a sound and it makes a very distinct sound so let's imagine that these two lines right here are your hands and when you clap your hands the lines move towards each other so your hands are moving towards each other and they're moving towards each other fairly quickly now in between your hands are a whole bunch of little air molecules which I'm drawing and uh and these air molecules which I'm drawing right now are these little let's imagine that they're these little purple dots so in between your hands are a whole bunch of these air molecules and so they're just floating around doing their thing and then all of a sudden the hands are moving towards each other and so all of a sudden the space that these air molecules occupy gets a lot smaller so a little bit later in time as the hands are moving towards each other so here we are just drawing the hands almost about to touch so what happened was all these air molecules that were just floating around they had all this space now all of a sudden they're really compressed so they're really really close together and they're super compressed they're very compacted now so you can imagine that as your hands are even closer together that the air molecules get even more compacted and so basically what is effectively going on is the air molecules here are getting pressurized so as you bring your hands together you're actually adding all the molecules up and it creates this pressure so this area of pressure actually tries to escape so it tries to escape and it kind of goes this way it tries to escape out wherever it can and so as its escaping it creates these areas of high and low pressure and that's what I'm representing here by these lines and these areas of high and low pressure are what are known as sound waves so we could have different types of sound waves we could have sound waves that are really really close together or really far away from each other and so if we draw this graphically it might look something like this so basically what I'm drawing here is up here would be an area of high pressure over here would be an area of low pressure and so basically there are just areas of high low pressure and how close these these Peaks are together is the frequency so if I clap my hands even even faster together or if there's something else that's a higher frequency a higher pitch sound the sound waves would be closer to one another and it would look something like this so depending on the frequency of a sound wave it's perceived to be different a different noise so let's imagine that this sound wave right here is f1 and that this one over here is f2 now sound waves of lower frequency actually traveled further so this is also this actually happens in the ear so these lower frequency sounds actually travel further and they actually penetrate deeper into the cochlea which is a structure that we'll talk about in a little bit so if you look at these two different sound waves they both have different frequencies but you might have noticed so let's imagine that this frequency f1 is generated by a hands clapping and f2 is generated by somebody talking so you can actually listen to both somebody talking and clapping their hands at the same time and what that would look at like if we were to these two frequencies together would be something kind of weird it might it might look like this it's not very uniform so if you were to add the two frequencies together you get this really weird jumbled frequency which we will label f3 now your ear has a very difficult task now because it has to actually break this frequency f3 down into the two simpler frequencies f1 and f2 and your is actually able to do that and it's able to do that because the sound waves actually travel different lengths along the cochlea so now that we've talked about what a pressurized sound wave is let's look at the hair cells and in general let's look at the anatomy of the ear ok so here we have a diagram of the hair and like I mentioned before there are sound waves that will be coming in to the ear so imagine that I clap my hands now sound waves are going to travel through the air and they're going to go towards your head and the very first thing that they hit will be this outer visible part of the ear so this is when you look at someone's here this is what you see and this outer visible part of the ear is something known as the pinna something known as the peanut so these sound waves get funneled by the pinna down into this smaller structure known as an auditory canal and this is also known as a external auditory meatus so I'll write that down here so external auditory meatus so these sound waves travel down the external auditory meatus and the next thing that they hit is the eardrum or tympanic membrane so the next thing that they hit is the eardrum now what the eardrum does is it actually starts to vibrate so as this pressurized sad wave hits the eardrum the eardrum starts vibrating back and forth and when it's vibrating back and forth it actually causes these little bones so there are three little bones here 1 2 & 3 and it causes these three little bones to vibrate the first bone is known as the is the second bone is known as the incus and the third little bone over here is known as the stay piece so let's just recap real quick so the sound waves come in get funneled by the pinna into the external auditory meatus otherwise known as the auditory canal then hit the eardrum otherwise known as the tympanic membrane and the eardrum starts to vibrate back and forth and this vibration causes three little bones known as the malleus incus and stapes to vibrate back and forth accordingly so the next thing that happens is the stay piece is attached to this oval window over here so it's known as the elliptical window which I'm underlining here it's also known as the oval window so this oval window starts to vibrate back and forth as well so the next thing that happens is there's actually fluid so this structure that the oval windows attach tube is known as the Copa so this round structure right here is known as the cochlea so inside the cochlea is a bunch of fluid and as the oval window gets pushed inside and outside of the cochlea by the stampedes it actually pushes the fluid so it causes the fluid to be pushed this way and causes the fluid going all the way around the cochlea and then it keeps going all the way around the control reaches the tip of the cochlea now when it reaches the tip of the cochlea what does it do well the only thing I can do is go back and so now the fluid is going to have to go back so I'll just follow this green line over here so the fluid moves back towards where it came but it actually doesn't go back to the oval window it actually goes to this other window known as the circular or round window you just fix that so goes to this circular or round round window and it causes the round window to get pushed out so this basically keeps happening so the fluid moves moves all the way to the tip of the cochlea all the way back out and back and forth and back and forth until the energy of this sound wave actually causes the eventually the fluid stops moving all that energy is dissipated and while hair cells inside the cochlea are being pushed back and forth and that transmits a electrical impulse via this auditory nerve to the brain now the reason that the fluid doesn't move back to the oval window when it goes to the very tip of the cochlea is because in between in the very middle of the cochlea is a membrane okay let me let me use a different color so there's actually a membrane so I'm going to use this black line to kind of demarcate the membrane that is that runs along the length of the cochlea so this membrane is something known as the organ of Corti let me just write that down here organ of Corti now this organ of Corti is actually composed of two different things it's composed of something known as the basilar membrane and something another membrane known as the tectorial membrane tectorial membrane so one final thing that I just want to touch upon is a general classification of the different parts of the here so this outermost part of the ear so from the pinna all the way to including the external auditory meatus so all the way to the tympanic membrane and including the tympanic membrane or eardrum is known as the outer or external ear so next from the malleus all the way to the stay piece so these three bones are known so from the malleus incus and the stapes that is known as the middle here so it looks like there's overlap but I'm just trying to include this word over here so the middle here is actually this region from here to here's the middle here whereas the external here is the region from here all the way out here and then the third section includes the cochlea and the something known as the semicircular canals which we didn't talk about and that is known as the inner ear so this is the inner ear so those are the three different general classifications that we could break the ear different structures of the hair down into and so next what I want to do is look at the organ of Corti yet or look at the cochlea a little bit more carefully and look at how the fluid motion inside the cochlea actually causes hair cells to fire a neural impulse to the brain which can then be interpreted as sound