[Music] if you're wondering what song i'm listening to the better question is how am i able to hear a song in the first place you see all that's coming out of these airpods are vibrations yet my brain is able to perceive music and song lyrics so in this video i thought we'd break down the auditory pathway and make sense of this together and in the meantime i'm gonna return to my vibrations [Music] i still find it fascinating that there aren't actually words coming out of my mouth even though you think there are but rather through the help of my vocal cords and other structures i'm just producing vibrations that are traveling through the air and through the magic of your ear and your brain you're able to interpret and make sense of these vibrations as words that you can understand so i thought we'd start this video by trying to understand sound itself and then how your brain interprets that for meaning all right let's start with this as i said in the introduction most of us probably listen to music right but there aren't actually lyrics coming out of these airpods or earphones but rather these are vibrations that are pushing up against what we call air molecules which then push up against other air molecules causing what we know as sound waves right and these are traveling through the air and they're going to enter your ear now to break down sound waves even more there's two really important concepts we need to know frequency and amplitude so let's break this down together let's start with frequency now frequency well right up here frequency helps determine what we know as pitch right pitch can be high and pitch can be low high and low and we determine the pitch by peak to peak right how close these waves are together now here they're very close together and this is going to produce a very high pitch sound as opposed to something that would be very spread apart right these waves are spread apart this would be considered a very low pitch right something like a trombone so pitch is determined by the frequency we also have as i draw a different wave amplitude and amplitude determines how loud a sound is whether it's very loud or very quiet and rather than peak to peak amplitude is determined by the height of the wave so the higher the wave the lower it is so this would be a very loud wave well this would be a very soft wave very very quiet you're at a library and you got a whisper so we'll say quiet and let's just write amplitude equals loudness just so we don't forget all right frequency is pitch and amplitude is loudness now to understand the ear we're first going to break it down into three major parts and each one has a different function so let's start with the first one we have our outer ear we have our or external we have our middle ear and we're going to break each one down and lastly we have our inner ear now all three parts or divisions help us hear the world but the difference is really with the inner ear because the inner ear is where something really magical happens this is where vibrations or sound waves convert into electrical signals right everything your brain needs to make sense of things with electrical signals in addition it also helps with balance and posture so i don't fall over so there's a little distinction of the inner ear we'll get to that in a moment all right let's start with the outer ear here are a few major components the first one is a thing that you can see with a naked eye you could touch it a lot of people have this pierced this we call the pinna okay where's the pinna it's this structure right here that all of us are holding and what is the purpose of the pinna to collect the sound wave okay and to funnel the sound wave okay to funnel the sound wave into the ear as opposed to going away from the ear so the pinna collects the sound wave and moves it forward towards the brain now it's going to pass down this little passageway do we know what that's called this is r i'll write it inside the ear or auditory canal canal okay and the purpose of the auditory canal is to take the sound wave and move it towards the brain for processing all right so this is the extent of the outer external ear the pinna and our auditory canal and this is where we enter we call the middle ear now there's a few structures with the middle ear we have our tympanic membrane which you probably know is the ear drum and these three really tiny bones called the oscillos all right now what is the purpose and what they do let's dive into that all right here's the first one the first one is this little drum here called what we call that the tympanic membrane okay and i said before you probably know this as the eardrum okay where is it it is right here and this we go from sound waves to vibrations so the middle ear is when vibration mechanical physical vibrations start to begin so let's write that in together this is when we start to see vibrations okay in addition this is when those vibrations are going to start to amplify okay now what do i mean by amplify or intensify it means that these vibrations have to get stronger and stronger and stronger as they head towards the inner ear because we'll get to this in a moment there's a lot of fluid inside the structure in order to move fluid you have to have more pressure imagine trying to jump up and down in a pool you need more energy than let's say jumping up and down right now so the middle ear we have vibrations and we also amplify those vibrations as we head towards the inner ear we also as i mentioned before have these three tiny bones do you remember what those called the ossicles all right these are the three tiny bones now what are these called this is important we have the malleus we got three different names we have these and i'll do a little arrow to point to the malleus we have the incus okay which is the middle one and lastly do we notice called the stapes okay the stapes is the third one now there are other names you might call this for example the malleus we might know is the hammer right all abbreviated names the incus the anvil the anvil and the stapes would be the stirrup so these are if you ever hear these names these are just kind of other names for the hammer than the incus and the stapes and the reason we call the hammer the animal and stirrup is because that's what they look like under a microscope it looks like a hammer an anvil is what you would drop on someone in a cartoon and a stirrup is you know what you put your foot in when you ride a horse so the malleus the yankees the incas and the stevies right this is all the middle ear and helps vibrate and amplify that sound all right we now enter the most important part the inner ear now before we get to hearing let's talk about the balance structure i was talking about originally you see these three little loops right here these we call the semi semi what semicircular canals okay now what do these do well just like the cochlea we'll get to that in a moment are filled with fluid as well as these little tiny hair cells okay that run all along these tubes and when this fluid moves what it's doing is giving back feedback okay it's giving feedback to the brain feedback to the brain about the body's position in space right am i bent over am i going forward am i going backward to make sure that my posture is all good right telling my brain where i am in space and we call this the specific sense our vestibular sense our vestibular sense what is it our vestibular sense and don't get this confused with our kinesthetic sense that's more proprioception like where your arms and legs are this deals with more and i'll put this in parentheses balance and body posture okay so there's the inner ear first we have balance posture or semicircular canals all right let's get back to hearing this structure right here is where all the magic happens all right this is we call the cochlea okay and my students once raised your hand says coachella i'm like no coachella is a concert in california this is the cochlea don't get that confused okay now what is the cochlea well the reason this is really important is because first let's talk about the shape of it it's shaped like a snail and that's actually what we call the cochlea okay so it's kind of a snail-like you know structure [Music] okay but also this is where transduction occurs all right what do we know about transduction we talked about this in other videos this is where sound right converts into electrical signals called action potentials and this happens in the retina for the eye and it happens in the cochlea for the ear so we go from sound to electrical signals now within the cochlea is a lot of fluid right and you got to have that fluid move which is why the uh the type of membrane along with oscillates are going to amplify those vibrations into stronger vibrations to make that fluid move now what i've done here is i actually have a cross-section of the cochlea itself okay in other words if you take the cochlea and you cut it in half this is what we see anything stand out to you well within the cochlea are essentially these three chambers okay and the most important one is the middle one what why is that because in the middle is what we have a you know essentially a sound recording organ called the let's do this together the organ do you really going with this organ of corti okay this is where all the specialized cells and receptors help convert the uh vibrations into electrical signals okay now what are the structures within the organ of quantity well there's a few of them what runs the length of the cochlea we'll start with the first one is what we call the basilar or basilar membrane okay it's kind of the floor of the cochlea and it runs the entire length okay what is the structure called and by the way we'll see the structure here i'll do it as a dotted line okay this is what the basilar basilar membrane okay write it down here okay now this membrane and those membranes all over contain a lot of specialized cells on top of it the most important one being what we call stereocilia okay i'll draw a little hair cells above here okay and when this fluid starts to move right we go from mechanical movement to fluid movement starts to move from these vibrations that enter through the oval window right malleus ink stapes the stapes is pushing against his oval window causes this fluid to vibrate as well this in turn is going to cause the basilar membrane to vibrate like a wave once that vibrates that's going to cause the stereocilia to vibrate and cause what an action potential okay where is that action potential going to go well it's going to travel via the auditory nerve okay to the brain for processing this is a nice way to break down how we hear now this is really important not every sound is going to cause every single hair cell to vibrate it actually depends on the frequency for example high frequency sounds are most likely going to stimulate or encode the cells on the base of the cochlea okay so on the outside right this is this is the base this would be what we call high frequency okay so high frequency sounds are going to be stimulated on the outside while in the middle this is called the apex we're going to have low frequency sounds that are very deep so high frequency sounds are going to stimulate the cells on the outside of the cochlea low frequency sounds are going to stimulate the cells on the inner or apex of the cochlea that's really important to know all right let's move on to our final destination right all right we have our sound waves under the auditorium canal that's going to cause the tympanic membrane along the ossicles to start to vibrate the stirrup or stapes is going to push up against the oval window to cause fluid vibrations this is going to lead to transduction where does it go from there let's take a look at this right here so we have our sound waves right traveling and once the sun rays turn to action potentials i'll use a different marker those are going to travel via the ear they are going to synapse in the brainstem and travel up to do we know the structure is the thalamus or thalamide because we have two of them i like to consider thalamus the sensory pit stop right all of our senses except for smell make it pissed out there and the thalamus is like where should we send these signals right they decide where everything goes and this will eventually synapse as a synapses here with the auditory what the auditory cortex right this is where sound is processed okay what is it called the auditory cortex okay which is right here in red right on the side now do we know what lobe will find the auditory cortex if you were thinking make sure i got that x the temporal lobe then you are right our temporal lobe okay so this is where sound is received the pitch right the the amplitude right we're understanding the tone and then your brain is like have i heard this before because now it has to do it has to connect that information with other memories right here's another view of it as well here's a side view right lateral view our auditory cortex would be you know right around here and what this is going to do it's going to connect with other parts of the brain say do i know this song right have i have i experienced this song before right because we have to make connections and to other things going on as well alright guys thanks for watching i really hope you enjoyed this video shout out to one of my students jessica rodriguez for helping with some of the diagrams behind me don't forget to like the video subscribe see you next time