Full transcript
0:00Greetings to all my followers, welcome to a new video of easy anatomy by Juán José
0:04Sánchez and today I bring you the third and final installment of ear anatomy,
0:10specifically we will then talk about the anatomy of the inner ear, in previous videos
0:16we addressed the ear external, the middle ear and today well of course the last portion as I
0:24have been telling you in the first videos we talk about the external ear, its two portions which are the
0:28pinna and the external auditory canal; then a second installment of ear we talk about
0:34the tympanic cavity which is the middle ear itself and today then we will address the inner ear which is
0:42made up of a group of structures called together the labyrinth, since they are
0:46quite complicated structures anatomically, the The route literally seems like a labyrinth
0:53and this labyrinth in turn is formed by the cochlea, also called the snail, and the
1:00semicircular canals, as well as other structures such as the vestibule in more depth.
1:06Now, getting into the subject, today we will talk about the inner ear, the inner ear. It is composed, as
1:14I told you, of a group of structures that have a labyrinth shape due to the complexity of their
1:22route, so we will mainly talk about the snail, also called the cochlea,
1:26we will talk about the vestibule, which is the entrance to the internal auditory canal and also its exit,
1:32and now Through the vestibule, the semicircular canals or ducts that we will address
1:38in this video also emerge, both structures of the inner ear. In the end, what will form me are the two
1:43most important nerves of the ear, which are the nerves that carry hearing and balance,
1:49because something important about the inner ear is that it is not only responsible for hearing,
1:54but rather through the vestibule and semicircular canals it is
1:59responsible for regulating body balance, which is why the The nerve that emerges from it has two
2:05roots, a nerve that comes from the cochlear nerve, which is the cochlear nerve, and a nerve that comes from the vestibule,
2:11which is the vestibular nerve. Together, at the junction of the vestibular nerve with the cochlear nerve,
2:16it is known as the cochlear nerve. vestibulocochlear or auditory nerve which is the famous 8th cranial nerve,
2:24you already know that it is then responsible for hearing and balance; so we are going to discover what
2:29the detailed anatomy of these structures of the inner ear is. Don't detach yourself from the video
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3:02access the full content of my videos. So this inner ear is made up of
3:08everything that is the labyrinth, here all these structures that we are seeing are those of the
3:13inner ear, this face that we are seeing is the external face, that is, it is what we see from
3:18the ear, it is It is very important that you master the anatomy of the middle ear, especially the external one, which
3:25matters so much to understand the internal ear, but you do have to master the anatomy of the middle ear in
3:30my previous video so that you can understand this inner ear perfectly. So this
3:35external face is the one that sees towards the middle ear and the face that we do not see, which is the one that sees,
3:39would be the internal face, the medial face, which is the one that sees towards the skull, so this labyrinth
3:45is made up of two large structures. a first portion of the labyrinth, which is the so-called
3:52bone labyrinth, which is the bone part, is the part of the bone, specifically the temporal bone, that
3:59makes up the structures, but in addition to this bone labyrinth there is another white structure
4:05that is cut, all labyrinths see that there are some spaces, those spaces are united, they are
4:11better said filled by another structure that you see that follows the same routes of the bone labyrinth
4:18but that has a let's say membranous composition and this is then the membranous labyrinth,
4:26so that the membranous labyrinth is located immersed inside or covered protected by what
4:33the labyrinth is, both labyrinths are important so that hearing can occur, see here a section
4:42again of the bone labyrinth, all that you see that is whitish in this image corresponds
4:49to what is inside the bony labyrinth, that is, the membranous labyrinth, or see here
4:53then all these structures that you see in blue are those that make up the membranous labyrinth,
4:58while the bony labyrinth would be all these structures typical of the temporal bone,
5:06Now, let's start talking about the bone labyrinth first. If you master the
5:10bone labyrinth, you will see that the membranous labyrinth will be much easier.
5:15The first thing you need to know about the bone labyrinth is that it occurs specifically in this bone
5:21that is the temporal bone, all the structures of the inner ear are found within the
5:26temporal bone more specifically in the portion of the temporal bone, through that
5:35temporal bone there is a hole called the external auditory foramen or canal, internal forgiveness ,
5:40or internal auditory canal through which the eighth cranial nerve comes out, which is what I told you
5:45is the vestibulocochlear nerve, carrying then the information it brings from the vestibule
5:50and semicircular ducts and the cochlea to what is the brain, carrying the
5:58position information Regarding balance and information regarding hearing, then
6:04see here this section here you can more or less see the semicircular canals, here would be the face,
6:10see what that is like, I brought you this image so that you understand that those structures are their own of this
6:16bone that you see here, which is the temporal bone, then this bone labyrinth as we are
6:21seeing it here, I remind you that we are seeing its external face, it will be made up of two parts
6:28or two important structures, first, what is the otic capsule? What is the otic capsule?
6:35The otic capsule itself is the same bone, that is, it is the endosteum of that temporal bone, the
6:42bone itself, the shell itself is the otic capsule, optical house, referring to the ear,
6:51now all the structures that are internal, That is to say, the gap, the space that is,
6:57let's say, covering the entire otic capsule, is the perilymphatic space, that is, all this bone that
7:05you see here is the otic capsule, which you will see is bone, while all the space
7:12that is located inside, that is, let's say the lumen of that otic capsule is the perilymphatic space,
7:19this is the otic capsule while what is inside the perilymphatic space, again here
7:24all this is optic capsule and all the space that is here is called perilymphatic space, something
7:30important is that there is a liquid that is inside the bone snail, the bone labyrinth, sorry, all
7:36that liquid that is inside that cavity is the so-called perilymphatic fluid, it is the
7:43perilymphatic fluid that is responsible for transmit the vibrations that come from the middle ear,
7:50that is why the space is also called perilymphatic space thanks to the fact that inside it
7:56there is a liquid that is the perilymphatic fluid, now what are the portions of this
8:02bone labyrinth going to be? ? a central portion that is the one that receives me to the structures of the middle ear
8:08communicates it with the middle ear, it also communicates it with the skull which is the so-called vestibule, from
8:14this vestibule the other 2 portions are joined, one is the ducts or semicircular canals,
8:20we will see it in more detail and the others are the bony snail, which is good enough to tell you that you see
8:26the snail shape that it has from there its name derives, the other anatomical name is cochlea. Let's
8:31start then first with the structures that are inside the vestibule, first on
8:37the external face which is the one that communicates it with the middle ear we are going to find the large
8:43oval window, that oval window is the one that is covered by the bone of the stapes, so when you saw the
8:50middle ear in the previous video I told you about a stapedic tympanic joint, which was the one
8:55between the base of the stapes and this oval window that is part of the external face of the vestibule
9:02, specifically the bony labyrinth, Now we cut to enter the
9:10perilymphatic space within the bone labyrinth and we find a series of depressions at the level of the
9:15vestibule, the most depression, remember that this is anterior, this is posterior, okay? highlighted
9:21is the external one, it is the one that we see over there, it is the internal one that we cut, the external face was that
9:26of the oval window, then we see a set of three fossae, the first fossa is the so-called
9:31elliptical fossa, then in the elliptical fossa we will find the emispheroidal fossa also called
9:40simply spheroidal fossa, these fossae house some structures of the membranous labyrinth that
9:46when we see the membranous labyrinth you will understand it at once I tell you that the
9:51elliptical fossa contains me to the utricle and the spheroid fossa contains the sacculus, later
9:58you will understand what the utricle means and what it means sacculus, lower down you will find a fossa that
10:04is the cochlear fossa, so called because it is what unites me to the cochlea with what is the vestibule,
10:12That is why it is called the cochlear fossa, now see a series of holes that are called
10:19fenestrae and are found on the inner face of this vestibule, well, these fenestra penetrate
10:25the roots of the auditory nerve to form on its inner face the auditory nerve itself, Now
10:32notice that inside the elliptical fossa there is a large hole looking medially,
10:37that hole is called the vestibule aqueduct, through there passes an important structure that is
10:43the endolymphatic duct that we will also see later in the membranous snail so
10:48see that I am telling you things that you have not seen but that when I explained the
10:52membranous snail that is inside the bone you will understand why these fossae are formed, now something important
11:00about the bone labyrinth specifically its vestibular portion is that it also receives me to the
11:06ducts semicircular canals, we are going to begin to then talk about the
11:11circular canals as you can see there are three: an anterior semicircular canal, a
11:16posterior semicircular canal and a lateral semicircular canal, those semicircular canals lead
11:26into what is the vestibule portion, if you are Seeing that each semicircular duct has
11:33about two branches, a branch of origin and a branch where it will reach again, it is to be thought
11:38that we are going to find six orifices, that is, two for each duct at the level of the vestibule,
11:44but it turns out that only We found five orifices and that is because there is a
11:50common branch or common duct that joins the anterior semicircular canal with the
11:56posterior semicircular canal. The canal as a whole will open as one at the level of the vestibule;
12:02Now see that there are dilations in the places where these ducts open,
12:09these dilations gave the name of ampulla and this would be the ampulla of the
12:14anterior semicircular canal or they are also called canals, this is the ampulla of the lateral semicircular canal and this
12:19is the ampulla of the duct posterior semicircular canal, now the anatomical exposure of
12:26these semicircular canals is important. Note that the anterior semicircular canal
12:31with respect to the posterior one has a first vertical plane and between them they form an angle of 90
12:37degrees, while the lateral semicircular canal follows a more plane very horizontal
12:43perpendicular also to the other two forming 90 degree angles, we see it much better in
12:49this image in an anatomical position, notice how the anterior with respect to the posterior is in
12:54a vertical plane and they form an angle here at 90 degrees but if we say We compare these
13:02anterior and posterior ducts with respect to the lateral one, we see that the lateral one is horizontal and that between them,
13:07there will also be a 90 degree angle. This atomic arrangement is very important to regulate
13:14what balance is, so we are already talking about the vestibule of the ducts. semicircular let's
13:19talk then about the bone snail, this is one of the most tangled structures of the inner ear,
13:24this bone snail is first a structure that you see is circular, the tip of the bone snail
13:32is the one that looks to the side, it is said that even look to the side and slightly anteriorly and
13:38that's where they form me, listen carefully to the promontory that we see on the inner face of the middle ear,
13:44the promontory is due to the tip of this snail while its base is the one that looks towards the which
13:50is the middle cranial fossa, that is, towards the skull medially, then the number of
13:56turns that this bone snail makes is said to be approximately 2.5 turns, let's go now then
14:02the arrangement of this snail, I hope you understand it well because it is a little tangled , here in this
14:07image I show you the internal or medial face of the middle ear canal and we then see how
14:13this elevation that is the promontory is made by the tip, by the vertex of the bony snail
14:18that is located further medial, so the first thing you have to know Guys,
14:24to understand the snail is that it coils but it coils around a structure,
14:29that structure that acts as an axis is the famous modiolus, we also call that modiolus an axis
14:37or it is also called a columella just as columella sounds with C with e, now That modiolus is the
14:45bone structure, it is a bony axis around which the snail coils, it will have a base and
14:50a vertex, you know that the vertex is what will form the promontory in the middle ear and the
14:56base is what that is going to look towards what is the middle cranial fossa at the level of the skull, then well,
15:02another bone structure is wound around this modiolus as if it were a spiral, that bone structure
15:10is what is called bone spiral sheet and it is that bone spiral blade which makes one turn
15:19as you see here, again another turn this would be the second turn and it almost makes the third turn
15:24that is why it is said that it makes approximately every two and a half turns, the bone spiral blade
15:30on the modiolus , see here so that you understand more or less this would be anterior, this is medial,
15:37this would be the axis as it gave the this that comes in the center and see how this structure that is
15:45sticking to the modiolus what they would be is, this is the spiral sheet, so that you have an idea,
15:50it is as if the modiolus were a nail, a smooth nail, and the bone spiral sheet would stick to it
15:57so much and turn it around that it would turn into a screw, this is the anatomical description as it
16:03is. What does the bone spiral lamina do with respect to the modiolus is like turning a nail into
16:08a screw, now what you see here would be the modiolus itself, which is the axis, and these structures
16:15that are sticking to the modiolus would be the osseous spiral lamina, this that you see in the center. Now,
16:22that modiolus, this spectacular image I found on the internet, I didn't get its bibliography but
16:27I would love to explain the modiolus and bone spiral sheet with this image, notice
16:33this cone that you see here is the column on the side of the modiolus, you already know that it has a vertex and a base,
16:40now imagine that this bone structure is also the spiral sheet, see here now
16:47the image below how the module converted what is a cone practically together with the
16:54spiral sheet, it turned it into a screw if you see how The bone conch itself is now contoured,
17:02that is, the cavity of the tube is coiled through the modiolus but it is coiled through the
17:12spiral lamina in the modiolus, so that if I put this spiral lamina like the average one
17:18that is this part of the center and in the middle I turn it and I follow that tract with a
17:25tube, imagine with a hose I can join what is the bone snail to what is that wall, so
17:33that it would be something like this, this would be the columella or modiolus, this would be the tube itself but you already know
17:38that in the center of the tube first is the spiral sheet, that is why when you see this
17:44image you see the spiral sheet here in the center and you see all this that is the tube itself,
17:49the bone snail itself that is rolled in turn in relation to the bone spiral sheet, ok? Now
17:59, from this spiral sheet come the structures that make up the membranous snail
18:06that we will see later. These sheets that we will see later divide this cavity
18:12of the bone snail into two subcavities, one that is towards the anterior and is called vestibular scala
18:19and one that is towards the back, which would be the scala tympani, both vestibular and tympanic scalas,
18:27only one part never joins, which I am going to explain to you because they are always between them
18:33as it is the membranous snail itself, that is, this membrane does not It does not allow the scala vestibuli
18:39or the scala tympani to join, now see it here in this image so you can understand it better. Look at
18:46how the snail is coiled around the tube and what you see in blue is the middle scala, that is,
18:52it is the membranous snail, notice. I have a ramp left towards anterior, which would be the vestibular ramp,
18:58which is called that because it goes towards the vestibule, it goes around the entire snail until it reaches
19:03to the tip, to the vertex, to the center of the snail, this tip or vertex is called helicotrema,
19:10just as helicotrema sounds and that helicotrema is the place where this vestibular scala is going to join
19:16and it is going to return and it is going to now begin to make scala tympani See here how it goes down
19:22in another direction, I know you didn't understand it well, let's see then the next image
19:27this would be the lobby, remember, okay? Let's say this groove that you see here would be what
19:34I explained to you just now, which was where the utricle was housed, which was the ellipsoidal fossa, and this
19:40fossa that is here, which is the spheroidal fossa, was where the sacculus was housed, which is this, so
19:45all of this is the vestibule remember that its external face was the opening of the oval window,
19:50notice then how this part that begins with the snail or that continues
19:55with the snail as it leads to the stimulus is the vestibular ramp the snail turns around until
20:01that reaches the center in the structure called helicotrema and there it is returned, which is now the
20:08orange part to form me, sorry, now it is the pink part, the orange part is the vestibular,
20:14the pink part to form what is the scala tympani and that scala tympani empties
20:21specifically in what we call a round hole, okay? round hole now or
20:31round window if you great what is the round window that is why I invite you to watch the
20:37middle ear video so that you can understand this, then notice this is the vestibule,
20:40this is the vestibular ramp see that it is a a little lighter, it reaches the center of the
20:46helicotrema and in the dark part the scala tympani begins in the opposite direction and that
20:51scala tympani, which is the darkest, see that it is specifically leading to the oval window,
20:56round, sorry, that round window that would be this, If we see it again, the vestibule, the
21:03vestibular scala reach the helicotrema and become the tympanic branch. This tympanic branch ends
21:09specifically in the round window. This round window is closed by a structure
21:13called the secondary tympanic membrane, which is a sheet of fibrous tissue. ,while you already
21:20know that the vestibule itself or the vestibular ramp ends in the vestibule which in turn is covered
21:25by what is the base of the stapes in the oval window, so this is a complicated structure
21:32of the bony conch then the membranous labyrinth So that you can finish understanding the snail or
21:39see that it is going to be much easier when I explain the membranous labyrinth, you remember
21:44that I told you that the bone snail inside had a liquid called perilymphatic fluids,
21:49well it is membranous. It has another liquid but in this case it is called the endo-
21:56lymphatic fluid or simply endo-lymph, so we are going to cut the bone snail to be able to understand
22:02how the membranous snail is made, which you will see are the same parts of the bone snail,
22:08let's To start first with the semicircular ducts, which is the least complicated,
22:13you see that these semicircular ducts that are found inside the
22:18bone semicircular duct are called the membranous semicircular duct, there is also an anterior one, a
22:23posterior one and a lateral one, they dilate when they open. Remember that I told you
22:28that it empties into the utricle, forming what is the membranous semicircular ampulla, so this
22:35would be the anterior ampulla, the middle ampulla and this the ampulla, sorry, this is the posterior one and this is the
22:40ampulla of the lateral semicircular canal, this would be the common membranous duct,
22:47they always have to add the word membranous at the end, now these semicircular ducts
22:53empty specifically at the level of the vestibule into a structure called utricle, now
22:59these semicircular ducts already know that they are the same names that we give to the
23:06semicircular ducts bone but the name changes to the level of the vestibule because we can no longer
23:10call this vestibule, vestibule in the bony part, for the membranous structures that are found
23:15inside the vestibule there are several, first we are going to talk about the utricle, the largest of which
23:20is It is the one that receives me to the five spaces of the membranous semicircular ducts, the
23:26Explain why there were five and not six, so the other structure that is found at the level of the
23:31vestibule is the sacculus, that sacculus is the one that continues with what the membranous snail is,
23:40now this sacculus and this utricle are joined by a duct. called the
23:50utriculosacular or sacculoutricular duct, this would be the utricular duct and this saccular duct,
23:55the two of them join together through that duct now at the junction of what is the sacculus with the
24:03membranous snail we find another duct, this is called the union duct or meeting duct,
24:10that is what the membranous snail then communicates with what is the sacculus and we are going to see
24:18that at the junction of the sacculus and the utricle there is a duct that is the endolymphatic duct,
24:25remember that when I was talking to you about The elliptical fossa, I told you that it was perforated by a
24:30hole, that was the hole of the lymphatic duct because that duct enters there, perforating
24:36the entire rock of the temporal bone, coming out through a hole that it has specifically in the middle cranial fossa,
24:41dilating, forming the endolymphatic sac which is a secular structure
24:48that is found below or outside the cranial dura mater, now let's look at it here, this
24:57would be the sacculus, this would be the utricle, this would be the sacculoutricular duct and this one seen
25:03here cut off would then be the endolymphatic duct, sacculo-utricle junction. Let's talk
25:13then about the membranous snail to conclude. that this membranous snail is joined to what
25:20is the saccule by the meeting duct, then this membranous snail follows the same path as the
25:25bone snail and what is different is that the one that is blue ends in a blind cul-de-sac
25:33, That is to say, when the vertex of the snail reaches, there ends a blind cul-de-sac, there
25:37is no communication or any place where that hole, that duct, comes out. Now we are going to
25:46take a good look at this image to determine what is inside the bony snail, this Remember that it was
25:52the spiral sheet, this was the bone snail itself, the tube of the bone snail itself,
25:57this was the columella or moliolus, so notice that through that spiral sheet
26:05two membranes originate, a membrane that we are going to see a lower membrane that we are going to call the
26:09bacillary membrane and a more superior membrane that we are going to call the vestibular membrane.
26:16You see that the bacillary membrane is inserted into what is the bone conch through this ligament that
26:22is an extension of the endosteum, it is nothing more than an extension of the endosteum, this ligament is
26:26called the spiral ligament, then this would be the bony spiral fold, this would be the
26:31bacillary membrane and this would be the spiral ligament. You know that this ligament that is being joined here
26:37is the vestibular membrane, so what I have left between the vestibular membrane and the bony conch itself
26:43would be the scala vestibular, what is left enters the bacillary membrane and the bony conch itself
26:49would be the scala tympani and what is left between is the scala, sorry in the membrane
26:57vestibular and the bacillary membrane is the scala media or simply called the membranous snail,
27:05so the membranous snail that this space that you see here. Now to complicate
27:09things a little more we see that above the bacillary membrane is the famous organ of
27:15hearing, thanks to it we can hear it is the famous organ of corti or spiral organ and
27:22above it we find this membrane that is the tectorial membrane, then these are the
27:27structures that we find inside what is the bony labyrinth specifically at the level
27:34of what is the cochlea, now how is this inner ear going to be innervated? This inner ear will
27:45be innervated or will carry its special insensitivity. You already know that what comes from the snail is
27:50the part of hearing thanks to the organ of corti with the auditory nerve, specifically
27:55its cochlear portion, while the one that comes from the ducts semicircular of the sacculus and
27:59the utricle of the vestibular portion, together this will then be the vestibulocochlear nerve
28:06passing through the internal auditory canal reaching what is the brain, specifically towards
28:13the midbrain as the eighth cranial nerve vestibulocochlear nerve or simply auditory nerve ,
28:19This one that we see here that is accompanying the facial nerve that has nothing to do with hearing,
28:23the irrigation is basically given by this artery that we see up here, which is the labyrinthine artery,
28:29also called the internal auditory artery because it goes through the internal
28:33auditory canal. , this labyrinthine artery can have two origins, one of this artery that you
28:39see below, which is the anterior-inferior cerebellar artery, or it can originate from two at the level of
28:46what is the bacillary trunk or the bacillary artery, but basically the entire irrigation of the The inner ear
28:52is given by this labyrinthine artery, whatever its origin from these two structures, the
28:57venous drainage is done through the petrosal sinuses, it can be done through the
29:01superior petrosal sinus or the inferior petrosal sinus. So friends, this has been the entire video,
29:07don't forget to subscribe in the little circle that appears here, here I leave you the links so you can see
29:12middle ear, external ear, don't forget to like the video, it is very important that you like it and you
29:18can follow on instagram at @juan_sanchez1315 thank you very much for watching the video and following me