Alright, so… have you ever stopped to  think about how sound actually works? 

I mean, how does a random vibration in  the air – like music, someone talking,  

or even the noise of traffic – somehow get turned  into something your brain understands as sound? 

It feels automatic, but the process behind  it is incredibly precise—and honestly,  

kind of mind-blowing. Because your ability to  hear depends on this small, complex system deep  

inside your head, where tiny bones vibrate, fluid  waves travel, and microscopic hair cells convert  

mechanical energy into electrical signals. And if any part of that chain fails – even  

slightly – you start to lose your ability to hear. So in this video, we’re going to go through  

exactly how that process works. We’ll  look at the external ear, the middle ear,  

the inner ear – and by the end of this video,  you’ll have a full understanding of how your  

body lets you hear the world around you. What’s up everyone, my name is Taim. I’m  

a medical doctor, and I make animated medical  lectures to make different topics in medicine  

visually easier to understand. If you’d like a PDF  version or a quiz of this presentation, you can  

find it on my website, along with organized  video lectures to help with your studies. 

Alright, let’s get started. So we’ll begin with the external ear, and  

this part is made up of three main components: the  auricle, or pinna, the external acoustic meatus,  

and the tympanic membrane. Let’s go through  each of these, starting with the auricle. 

The auricle is the visible part of the ear  that sticks out from the side of your head.

It’s made up of elastic cartilage which  gives it the flexibility to bend forward,  

upward, or twist in any direction,  and still recoil back into position. 

Now, externally, we divide the  auricle into several anatomical  

landmarks. And I recommend you to feel  those structures on your own ear as we  

go through them to activate more areas of  your brain for stronger memory formation.

The outermost rim is called the helix. Just  inside of that is a ridge called the antihelix.  

Between the two, there’s a narrow groove known  as the scapha. Closer to the center of the ear,  

we’ve got the concha of the auricle. This is that  bowl-shaped depression that leads directly into  

the ear canal, and it helps collect and  funnel sound. Then we’ve got the tragus,  

that small protrusion just in front of the ear  canal opening. Across from that is the antitragus,  

and between them is a little dip called the  intertragic notch. And at the very bottom,  

we have the lobule of the auricle –  the soft earlobe, which is unique in  

that it doesn’t contain any cartilage. These structures are actually clinically  

useful too. For example, the tragus is often  used in exams for signs of otitis externa,  

that is inflammation of the external ear,  where pressing on the tragus can cause  

pain. That’s one of the classic findings. Right beneath the skin of the auricle,  

we have a few more important structures. There are the extrinsic auricular muscles,  

which attach the ear to the skull. Then the intrinsic auricular muscles,  

which are small muscles within the auricle itself,  but these don’t have a real function in humans. 

You’ll also find the auricular cartilage making up  the core of the pinna, and nearby runs the facial  

nerve, or cranial nerve VII, which provides  motor innervation for the muscles of facial  

expression, including some around the ear. One more thing I want to mention here is  

sensory innervation, because the external  ear has a pretty interesting nerve supply. 

At the top portion, we have the  anterior auricular branches of the  

auriculotemporal nerve, which is a branch of  the mandibular division of cranial nerve V. 

The back side of the auricle is innervated by the  lesser occipital nerve, from the cervical plexus. 

Then, down at the bottom, there’s the great  auricular nerve, also from the cervical plexus. 

And the rest is covered by the  auricular branch of the vagus nerve,  

which is why stimulation of the external auditory  canal can sometimes cause a vagal response,  

like coughing. As weird as it sounds. So that was the auricle. 

Now let’s go inside the ear and look  at the external acoustic meatus. 

The external acoustic meatus is the ear canal – it  runs from the outer ear to the tympanic membrane. 

And anatomically, we divide it into several parts. At the opening, we have the external acoustic  

aperture. Just after that is the  cartilaginous portion of the canal,  

which makes up the outer third. Then, deeper inside, is the bony part,  

which makes up the inner two-thirds of the canal. These two regions also differ in sensitivity—the  

bony part is more sensitive to pain,  which is important to remember when  

examining the ear with an otoscope. Next to the tympanic membrane,  

we find the tympanic sulcus and notch, which help  anchor the eardrum to the walls of the canal. 

Now, along the skin of the canal,  especially in the cartilaginous portion,  

you’ll find ceruminous glands. These are modified sweat glands that  

produce something called cerumen, which is also  known as earwax. The earwax is slightly acidic  

and what it does is that it’s specialized to trap  things like dust, bacteria, and other particles,  

helping to protect the middle and inner ear. So that was the external acoustic meatus.  

Now let’s cover the last segment of the external  ear, which is the tympanic membrane, or eardrum. 

And it’s easiest to understand if you look at  it from this direction, and then isolate it. 

This is what your eardrum looks like. Now,  around the eardrum, we have something called the  

fibrocartilaginous ring. This is a thickened ring  that basically holds the eardrum in place within  

the tympanic sulcus. Now, the tympanic membrane  itself is divided into two main components,  

we have the pars tensa, which is a very very  heavily dense fibrous irregular connective tissue,  

the other one is called pars flaccida, which is  the upper, loose part of the tympanic membrane.  

And this is important because if you go and stick  a Q-tip into the ear and you accidentally hit the  

pars flaccida too hard you can puncture the  tympanic membrane. And that would affect the  

middle ear pressure as well as open up for certain  types of microbes to come in. Now, another thing  

we see is that we can actually see an outline  of the malleus, which is one of the ossicles  

located in the middle ear, but what it does is  that it’s pushing towards the tympanic membrane  

and forming an umbo of the tympanic membrane. It  forms the mallear stria, and a mallear prominence. 

Imagine now that you’re going to assess the  eardrum, so what you do is shine a light into the  

external acoustic meatus, you should be able to  see all of those structures, and as you do this,  

you should be able to see a reflection a light  reflex, or cone of light. Which basically is a  

reflection that once it’s visible, it indicates  a healthy eardrum during an otoscope examination. 

So that was basically all three parts of the  external ear. We finished the external ear,  

now let’s do the middle ear. So let’s zoom in. When you look at the middle ear, the first thing  

to understand is that it contains three tiny  ossicles, arranged in a very specific way to  

help transmit sound from the eardrum into  the inner ear. These are the smallest bones  

in the human body, and without them, we  wouldn’t be able to perceive sound at all. 

And the first one of those three ossicles is  the malleus. The malleus has a head, a neck,  

and then a long process called the handle of the  malleus, which is the part that actually attaches  

to the tympanic membrane. That’s the structure  we saw earlier forming the mallear prominence,  

the mallear stria, and the umbo. So every  time the tympanic membrane vibrates,  

that handle of the malleus is the very  first thing to pick up that motion. 

From the malleus, the vibration continues to  the next ossicle, the incus. The incus consists  

of a body, a short limb, and a long limb. And  that long limb is important because it directly  

articulates with the third ossicle, the stapes. The stapes has a head, an anterior and posterior  

limb, and then a flat portion called the base  of the stapes. And what the stapes does is that  

it sits right on top of the oval window,  which is the entrance into the inner ear. 

So right now, as you’re hearing my voice—or  any sound, for that matter—the soundwaves  

of that sound is traveling through the external  acoustic meatus, striking the tympanic membrane,  

and causing it to vibrate. Those vibrations  are then passed from the tympanic membrane to  

the malleus, then to the incus, and then to  the stapes. And each ossicle amplifies that  

vibration slightly before the stapes finally  pushes on the oval window and sets the inner  

ear fluid into motion. We’ll talk about that  fluid movement in detail later in the video,  

because that’s where sound, or mechanical  energy is transformed into electrical signals. 

But before we move on, there’s also an important  protective mechanism here. Imagine for a second  

that the sound is suddenly very loud—like a  sharp, unexpected noise. That kind of strong  

amplitude would cause significant vibration of  the tympanic membrane, and if nothing helped  

regulate it, the membrane could actually be  damaged. To prevent that, we have a small  

muscle called the tensor tympani muscle, which  attaches to the malleus and tightens the tympanic  

membrane to reduce the force of the vibration. Now. The middle ear is a cavity, right? And this  

cavity has walls. On the lateral wall, we have the  tympanic membrane, the one we just talked about.  

On the medial side, we’ve got the inner ear,  and anteriorly, we find the auditory tube. Now,  

the thing is, the middle ear is actually  an essential part of the temporal bone,  

and what makes it even more important is that  many different structures pass through it. 

If we look at it from this angle, and then  remove the facial bones, we’ll be able to  

see the temporal bone. And coming off from this  bone on the anterior side, is the auditory tube.  

This auditory tube has two distinct parts,  there’s a lateral bony part, which is rigid,  

and then medially, we have the cartilaginous  part, which is a bit more flexible. This tube  

extends all the way into the nasopharynx,  and its job is to equalize pressure between  

the middle ear and the outside environment. Now, the ear structures are located deep within  

the petrous part of the temporal bone, As you  see here, we can see parts of the external ear,  

the middle ear, and the internal  ear. Let’s zoom in for a moment. 

Can you see the middle ear structures now?  You can see the tympanic membrane forming  

the lateral wall, and behind it, we have the  malleus, the incus, and the stapes. You can  

also see the tensor tympani muscle, originating  from the cartilaginous part of the auditory tube,  

and inserting on the handle of the malleus. So. This is the middle ear. I know I’m  

overemphasizing this, but I’m doing it for a  reason. So imagine this, let’s say you casually  

walk across the external acoustic meatus. What are  you looking at now? You’re looking at the tympanic  

membrane, right? And remember, that membrane is  the lateral wall of the middle ear. Makes sense? 

Now. Let’s go ahead and remove the tympanic  membrane – imagine we’ve taken it out  

completely. That means now you’re looking  directly into the middle ear cavity. What  

you’re seeing is the cavity formed by six walls.  You’ve got the medial wall, the superior wall,  

the posterior, anterior, and the inferior wall. The medial wall is called the labyrinthine wall,  

because it’s the one that’s directly facing  the inner ear. The superior wall is called  

the tegmental wall, because it’s formed by the  tegmen tympani, which is a thin plate of bone  

separating the middle ear from the cranial cavity  above. The posterior wall is the mastoid wall,  

which connects to the mastoid air cells. The  anterior wall is known as the carotid wall,  

because the internal carotid artery runs right in  front of it. And the inferior wall is called the  

jugular wall, because that’s where the jugular  bulb of the internal jugular vein lies just  

beneath it. So that whole cube you’re looking  at, that entire space, is the tympanic cavity. 

So I’ve removed all the ossicles just  temporarily, so we can see everything  

more clearly. And what I want to do next  is take you through each wall one by one,  

and talk about all the landmarks and openings  related to them. Because if you understand these,  

it becomes way easier to mentally navigate the  tympanic cavity, and it’ll help you recognize  

what goes in, what comes out, and what’s at  risk during infections or surgical procedures. 

Let’s start with the labyrinthine  wall, which again is the medial wall,  

facing the inner ear. First, there’s the  promontory, which is a rounded bulge created  

by the first turn of the cochlea. Then, just  above that, we have the oval window, which is  

the opening where the base of the stapes sits.  Just below the promontory is the round window,  

which is covered by a flexible membrane called  the secondary tympanic membrane. These structures  

will make sense a little later in this video. From the inferior wall of the tympanic cavity,  

there’s a small opening called the  tympanic canaliculus, and through that,  

we have the tympanic nerve, which is a  branch from the glossopharyngeal nerve,  

cranial nerve IX. This tympanic nerve enters  the middle ear through the canaliculus and  

then spreads out over the promontory and forms  a nerve network called the tympanic plexus. 

Now, from that plexus, we get a branch called  the lesser petrosal nerve. This nerve exits the  

middle ear through its own canal, the canal  for the lesser petrosal nerve, and continues  

its path toward the otic ganglion, where it  eventually synapses and contributes to the  

parasympathetic innervation of the parotid gland. There’s another set of fibers that come from the  

internal carotid plexus, which surrounds  the internal carotid artery called the  

caroticotympanic nerves. These fibers enter the  tympanic cavity through the caroticotympanic  

canaliculi and join the tympanic plexus,  contributing sympathetic fibers to it. 

So, if we look at it in perspective, we can  actually see the glossopharyngeal nerve giving  

off the tympanic nerve, which enters the  middle ear and forms the plexus, from which  

the lesser petrosal nerve takes off heading up  toward the otic ganglion. And alongside this,  

we’ve got the internal carotid plexus, which  surrounds the internal carotid artery, giving  

off those caroticotympanic nerves, supplementing  the plexus with sympathetic innervation. 

Now let’s look at the posterior wall of the  middle ear, we can see the facial nerve—cranial  

nerve VII—running in its facial canal. As it  travels, it gives off a small branch to the  

stapedius muscle. That branch exits through a  small projection called the pyramidal eminence,  

and it’s within that little hollow that the  stapedius muscle sits. This muscle inserts onto  

the neck of the stapes, and when it contracts,  it pulls the stapes away from the oval window to  

dampen the vibration—basically acting as a second  layer of protection against loud sounds. That  

contraction is controlled by the facial nerve. Now while we’re talking about the facial nerve,  

another branch it gives off is the chorda tympani  nerve. That nerve enters the tympanic cavity  

through the posterior canaliculus, crosses  over the tympanic membrane and malleus,  

and exits through the anterior canaliculus  to go toward the infratemporal fossa,  

where it joins the lingual nerve. It carries  taste sensation from the anterior two-thirds  

of the tongue and parasympathetic fibers  to the submandibular and sublingual glands. 

If we now look at the anterior  wall of the tympanic cavity,  

one structure we see here is the tensor tympani  muscle. Remember this one originates from the  

cartilaginous portion of the auditory tube and  the greater wing of the sphenoid, and inserts  

onto the handle of the malleus. Again, helping  to reduce the amplitude of sound vibrations. 

Right next to it on the anterior side, we  also find the opening of the auditory tube, or  

Eustachian tube, which connects the middle ear to  the nasopharynx. This tube helps equalize pressure  

between the middle ear and the environment. So that was everything for the tympanic cavity,  

and with that, we’ve covered the middle ear.  Alright, now let’s finally do the inner ear,  

and figure out how we actually convert sound into  electrical signals that our brain understands. 

The internal ear is represented by the  vestibulocochlear organ. Let’s zoom in on  

it. This is such a beautiful little organ. I wanna  switch over to a 3D model for a moment to see it  

in detail. The inner ear is divided into three  parts—the semicircular canals, the vestibule,  

and the cochlea. This organ has two functions.  The semicircular canals and the vestibule are  

responsible for maintaining balance, while the  cochlea is responsible for hearing. Just before  

I continue, remember what these two holes were  called? The oval one is called the oval window,  

and the round one is called the round window.  Again here we see the eardrum, with the malleus,  

incus, and stapes, and it’s the stapes  that’s pushing against the oval window.  

The round window has a membrane, and that’s  why we call it the secondary tympanic membrane. 

Anyways, the round and oval windows will be  important very soon when we talk about the  

hearing mechanism, but let’s cover some more  structures of the inner ear first. Now, the  

vestibulocochlear organ is divided into two parts.  The outer shell is called the osseous labyrinth,  

and inside that, there’s a membranous  labyrinth. The osseous labyrinth is bony,  

and the membranous labyrinth is a  fluid-filled sac. Makes sense so far? 

The three parts we mentioned earlier—the  semicircular canals, the vestibule, and  

the cochlea—are regions that contain the osseous  labyrinth. Now let’s fade the osseous labyrinth  

and focus on the inside for a moment. Inside  the semicircular canals, we find semicircular  

ducts. We have an anterior, a posterior, and a  lateral duct. And there’s also a common membranous  

limb that connects some of them together. We can also see the utricle, the saccule,  

and the cochlear duct. And then we have the  endolymphatic duct, which leads into the  

endolymphatic sac. These lie deep to the dura  mater in the posterior cranium, and one thing  

to keep in mind is that the membranous labyrinth  is a closed system, it’s a poutch. And the fluid  

within it is removed by reabsorption via  the epithelium of the endolymphatic sac.

These are all part of the membranous labyrinth.  Other things we can see is the ampulla, which is  

the widened base of each semicircular duct. All  of these fall under the membranous labyrinth. 

So that’s generally how we divide the  bony and the membranous labyrinth. 

From personal experience, it makes so  much more sense to go through all of  

the structures of the inner ear before we talk  about the actual function. Now, this is where  

the interesting part of this video starts. Ready? Between the osseous labyrinth and the membranous  

labyrinth, we’ve got something called perilymph.  So, perilymph covers all of this area between the  

two structures. Within the membranous labyrinth,  we’ve got endolymph, which fills the inner  

compartments. These two fluids never mix, and this  is really important because even their chemical  

composition is different. The perilymph is similar  to extracellular fluid—so it’s high in sodium and  

low in potassium. Endolymph, on the other hand,  is similar to intracellular fluid or cytosol—so  

it’s low in sodium and high in potassium. This is super super important to know  

because it’ll come into play in just a  minute when we start talking about the  

function of the hair cells. And again,  remember: these two fluids do not mix. 

Alright, i’m gonna make you an expert in the  hearing system by the end of this video. Now,  

we divide the inner ear into a vestibular system  for balance, and a cochlear system for hearing. 

Let’s do the vestibular system first.  The vestibular system is made up of two  

functional parts: the three semicircular canals,  which detect rotational movements of the head,  

and the otolithic organs—the utricle and  saccule—which detect linear acceleration and head  

position relative to gravity. The semicircular  canals are arranged roughly in three perpendicular  

planes. The anterior canal is responsible for  detecting nodding motions like when you say yes,  

the posterior canal detects movements like  tilting your head towards your shoulder,  

and the lateral canal detects horizontal  head turns, like shaking your head no. 

Each canal has an enlarged end called the  ampulla, and inside the ampulla, we have the  

crista ampullaris. That’s the sensory organ that  responds to rotation. It consists of the cupula,  

a gelatinous structure that bends with endolymph  flow; hair cells, which are the actual sensory  

receptors; supporting cells; and fibers of  the vestibular nerve, which carry signals  

centrally. When the head turns, the endolymph  inside the canal lags behind due to inertia  

and pushes against the cupula. This deflects the  cupula, bends the stereocilia on the hair cells,  

and if deflected in the excitatory direction,  that allows potassium-rich endolymph to enter  

the hair cells. That depolarizes the cells and  sends nerve impulses through the vestibular  

nerve to inform the brain about the movement. Below the semicircular canals, we have the utricle  

and the saccule. The utricle is responsible for  horizontal acceleration—like when you accelerate  

forward in a car—and the saccule responds to  vertical acceleration, like when you go up or  

down in an elevator. Together, these are called  the otolithic organs. They each contain a sensory  

area called the macula. On top of the hair cells  in the macula lie tiny calcium carbonate crystals  

called otoconia, or otoliths. These are suspended  in a gelatinous layer and add weight and inertia.  

When the head accelerates in any of those planes,  the otoliths shift and drag the gel with them,  

bending the embedded hair cells. That bending  again opens channels, potassium flows in from  

the endolymph, depolarizing the cell and sending  signals through the vestibular nerve. If these  

crystals jump out of their place and enter the  semicircular canals, they can cause a condition  

called benign paroxysmal positional vertigo,  or BPPV, which leads to episodes of dizziness. 

So that’s the vestibular system, and signals  from here are carried to the brain via the  

vestibular nerve. Makes sense? That’s how  balance is perceived by the inner ear. Let’s  

now do the auditory system. This one is such  an interesting system. The auditory system is  

built within the cochlea. It’s divided into the  scala vestibuli, scala tympani, and scala media.  

These are wrapped around a central axis called the  modiolus, which is the bony core of the cochlea  

that houses the spiral ganglion and blood vessels. Now, if we take a cross-section of the cochlea,  

we’ll be able to see those three compartments  clearly. The scala vestibuli and scala tympani  

both contain perilymph, while the scala media  contains endolymph. Why does this matter?  

Well, when sound waves enter your external  acoustic meatus, they vibrate the eardrum,  

which then transmits that vibration through the  malleus, incus, and stapes. The stapes pushes  

into the oval window, transmitting that mechanical  energy into the perilymph of the scala vestibuli. 

As the stapes pushes inwards, it sends  a pressure wave through the perilymph,  

which is separated from the endolymph. That wave  travels up the spiral of the cochlea toward its  

apex. The end point where that fluid shifts to the  other side, is called the helicotrema. From there,  

the wave continues down the scala tympani and  eventually dissipates at the round window.  

The round window has a secondary tympanic  membrane that bulges outward to accommodate  

the pressure of the incoming fluid wave. Now, as the perilymph moves through these  

chambers, it exerts pressure on the membranes  that separate the scala media. The area above  

scala media is the scala vestibuli and  below is the scala tympani. Alright,  

we’ve come this far. So now you may ask, so Taim,  how does this system ‘’understand’’ sound? I’m  

glad you asked. And in order to understand  that we need to go through some structures. 

The vestibular membrane separates the scala  vestibuli from the scala media, and the basilar  

membrane separates the scala tympani from the  scala media. Vibrations in the perilymph cause  

these membranes to oscillate, and the most  important of these is the basilar membrane,  

because there’s a very important organ  attached to it, it’s the organ of Corti. 

Let’s zoom in on the organ of Corti, which is  the actual structure responsible for turning  

vibrations into electrical signals,  this is where hearing really happens. 

The main sensory cells here are the hair cells,  divided into inner and outer hair cells. The inner  

hair cells are the ones that detect sound and  send information to the brain. The outer hair  

cells help amplify the signal and fine-tune  the response. These hair cells are supported  

by different types of supporting cells — internal  supporting cells next to the inner hair cells, and  

external supporting cells next to the outer ones.  Between them, we see the pillar cells, which form  

a triangular space called the tunnel of Corti.  This is important for maintaining the structural  

integrity of the organ and helping guide how  vibrations travel across the basilar membrane.  

It also plays a role in isolating and organizing  the movement of the hair cells during stimulation. 

Sitting just above the hair cells is the tectorial  membrane, a gelatinous membrane that extends over  

the organ of Corti. And projecting from the  top of each hair cell are fine structures  

called stereocilia, which make contact with,  or lie close to, the tectorial membrane. 

When sound vibrations travel through the  cochlea, they cause the basilar membrane  

to move up and down. This movement  causes the stereocilia to bend. Now,  

these stereocilia are suspended within endolymph,  which is high in potassium and low in sodium,  

a composition that’s very different from the  perilymph that surrounds the rest of the cochlea. 

When the stereocilia bend in a certain direction,  potassium channels open, allowing potassium from  

the endolymph to enter the hair cell. This causes  depolarization, which leads to the release of  

neurotransmitters at the base of the cell. That  stimulates the cochlear nerve fibers underneath,  

and those signals are sent through the cochlear  nerve. So again, the basilar membrane vibrates,  

the stereocilia bend, potassium enters  the hair cell, the cell depolarizes,  

and a signal is transmitted through the cochlear  nerve, which passes the cochlear ganglion and  

then continues on to the auditory pathway. Now, what if I’m speaking in a low volume,  

or what if I’m speaking in a high pitch?  How does the system discriminate that? 

This is where everything is going to make sense. Now, we got the scala vestibuli, scala media and  

scala tympani. Imagine for a moment that we  roll out the cochlea, we’re just rolling out  

the whole cochlea. What we’re going to see  is the basilar membrane. Above the basilar  

membrane is the scala vestibuli, below  is the scala tympani. Makes sense so far? 

Imagine now that a sound is detected in  the external environment. That soundwave  

will eventually cause the stapes to push towards  the perilymph of the scala vestibuli. That wave  

of impulse is going to continue along the scala  vestibuli, and then loop around the apex. Which  

is called what? It’s called the helicotrema. The  wave impulse will continue along the scala tympani  

and then eventually reach the round window, which  basically bulges outward to release the pressure. 

Now. As the wave impulse travels along the  perilymph, some of that fluid is going to  

oscillate, or vibrate the basilar membrane and  cause it to react to that sound. But our body is  

so smart at discriminating the frequency  and amplitude of that sound. And it does  

that because in reality, the basilar  membrane looks more or less like this.  

The base of the basilar membrane, the  base closest to the round and oval window,  

is the narrowest. And not just that,  the base is also the stiffest. And this  

is perfect because the basilar membrane  here is tuned for high-frequency sounds. 

Towards the apex, the basilar membrane is the  widest and is very flaccid, and it’s tuned for  

low-frequency sounds. Now, humans can detect sound  frequencies ranging roughly from 20 to 20,000 Hz.  

We don’t commonly use the extremes of this  range, but we’re capable of perceiving them.

For example, if the sound has a frequency  of 1600 Hz, the wave will cause the basilar  

membrane to vibrate at a certain location that  is tuned to 1600 Hz. If the frequency is lower,  

say 400 Hz, the vibration will occur further  along the membrane, closer to the apex.

This is how the cochlea  separates pitch, or frequency. 

And now you might be asking, but Taim, what  if the person is speaking really loud? How  

does loudness affect the basilar membrane? Loudness is determined by amplitude, and that  

amplitude determines how strongly the basilar  membrane vibrates at that specific pitch. The  

louder the sound, the more intense the vibrations  will be at that specific pitch. The lower the  

loudness, the weaker the basilar membrane  will vibrate at that same pitch. Makes sense? 

So loudness is determined by amplitude.  And normal amplitude hearing for humans  

is around 0 to 120 decibels. We don’t usually  experience the whole spectrum in normal life. 

If you look here, a normal speaking voice  is going to be around 60 dB. And prolonged  

exposure to loudness of about 85 dB or more  is damaging to the ear long term, because it  

can wear out or even destroy those hair cells.  And once they’re gone, they don’t regenerate. 

So in summary, how strongly the basilar membrane  vibrates—that’s loudness. Can be low volume or  

high volume, measured in decibels. Where on  the basilar membrane it vibrates—that’s pitch,  

or hertz. Can be high-frequency  sounds or lower-frequency sounds. 

So. Balance from the vestibular system is carried  through the vestibular nerve. Hearing is carried  

through the cochlear nerve. They join together  to form the vestibulocochlear nerve—the eighth  

cranial nerve—which goes to specific areas of  the brainstem. And this path onwards is covered  

in the video about the vestibulocochlear nerve. And with that, we’ve now covered the detailed  

anatomy of the human ear, the organ of hearing  and balance. We’ve covered the external ear,  

the middle ear, and the inner ear. I  really hope you found that helpful. 

I’ve made free courses for other topics  here on YouTube if you wanna keep learning,  

otherwise if you want a handmade PDF  version of this lecture or take a quiz  

to test your knowledge, or access  an organized list of all my videos,  

you can find everything on my website.  Thanks for watching! See you in the next one.