00:01
Now, we can proceed to the middle ear.
00:04
And again, this is also referred to as the tympanic cavity.
00:08
There are three regions of the tympanic cavity.
00:11
The first one is that area just immediately medial to the tympanic membrane.
00:18
This is referred to as the mesotympanum.
00:22
Above that is the epitympanic recess, and epi does mean above.
00:32
And then, we also have an area just below the mesotympanum, and that's the hypotympanum.
00:41
Hypo means below.
00:43
When we're within the middle ear, the middle ear will have six walls.
00:51
Two of these six walls can literally be referred to as a roof and a floor.
00:56
So, these six walls would resemble the cube that we see in this particular orientation.
01:03
So, we'll quickly identify the boundaries or the borders of these walls.
01:07
The uppermost wall, the roof, is formed by the temporal bone.
01:14
Specifically, the region of the temporal bone called the tegmen tympani.
01:19
The floor or wall is the jugular wall.
01:25
Posteriorly, we have the mastoid wall of the middle ear.
01:32
Anterior wall is also referred to as the carotid wall.
01:40
Here, we're looking at the medial wall between the middle ear and the internal ear,
and this is referred to as a labyrinthine wall.
01:55
And then, lastly, we have the lateral wall,
which is also referred to as the membranous wall
because of the presence of the tympanic membrane.
02:06
The membranous wall, specifically in the tympanic membrane which we see here,
is forming the lateral wall.
02:16
We have some structures here that we'll point out
because of their association within the middle ear cavity
and in ear ossicles and the tympanic membrane.
02:27
And specifically, we're looking at the chorda tympani.
02:30
The chorda tympani is a nerve that arises from the mastoid segment of your facial nerve,
and we see the facial nerve right in through here.
02:39
The chorda tympani carries afferent special sensation from the anterior two-thirds of the tongue,
and this is via the lingual nerve.
02:48
And it also conveys afferent parasympathetic secretomotor fibers
to the submandibular and sublingual glands.
02:58
The medial wall or labyrinthine wall is shown in through here.
03:09
Again, this separates the tympanic cavity from the internal or inner ear.
03:14
The most prominent feature here is the promontory,
and also the round window that we see in through here.
03:24
And the oval window would be right where the stapes is located.
03:33
And the bulge that we see here that forms the promontory is a bulge of the cochlea.
03:44
That is a member of the inner ear.
03:48
Some structures within the middle ear.
03:52
First, there are some ligaments of the middle ear that are labeled here.
03:56
These well anchor the ear ossicles in place and we see the three ear ossicles here.
04:05
We'll identify them very, very shortly.
04:08
Also associated with the middle ear is the eustachian tube,
also known as auditory tube or the pharyngotympanic tube.
04:19
This is of communication between the middle ear and the nasopharynx,
and the eustachian tube functions to equalize the pressure
within the middle ear with that of atmospheric pressure.
04:34
Now, the ear ossicles, there are three.
04:39
We'll go through them, and then we'll finish up with a mnemonic,
and it's a can't miss mnemonic.
04:46
First, we have the malleus that's shown here.
04:50
The malleus would be associated with the tympanic membrane.
04:55
The malleus will articulate with the second ear ossicle called the incus.
05:00
And then, the incus will articulate with the stapes.
05:06
And the mnemonic for that is M-I-S, MIS.
05:13
M for malleus, I for incus, and then the S for stapes.
05:19
We also have a couple muscles within the middle ear.
05:27
These are very thin, delicate muscles
as you might think that they would be in a very small, confined area.
05:35
The first one is the stapedius muscle. You see it here.
05:39
As the name implies, it has an insertion on the stapes.
05:44
The nerve supply to the stapedius muscle is the stapedius branch from your facial nerve
and this protects the ear from sudden loud noises.
05:57
When the stapedius contracts, it will dampen the vibrations
that are being transmitted into the cochlea.
06:05
Through the oval window specifically.
06:08
The other muscle is a larger muscle,
but again, by muscle standards, it's still a small muscle,
and this is referred to as the tensor tympani muscle.
06:22
And the tensor tympani is attached to the malleus.
06:25
Its innervation is from the medial pterygoid nerve,
which is a branch of the mandibular nerve of the trigeminal.
06:35
It too will dampen and protect the ear against sudden loud noises.
06:43
All right. Now, we're looking at the blood supply of the middle ear.
06:48
Here, we have the superior branch of the anterior tympanic artery
that helps to supply the middle ear. This is a branch of the maxillary artery.
06:59
We also have the caroticotympanic artery.
07:03
This is a branch of the internal carotid artery.
07:08
We also have the inferior tympanic artery,
and this is a branch of the ascending pharyngeal artery.
07:16
And then, we have the superior tympanic artery that is also feeding the middle ear.
07:24
Some additional views to the blood supply to the middle ear are shown here.
07:30
Here's another view of the anterior tympanic artery.
07:34
As mentioned, this is a branch of the maxillary artery.
07:38
The incudal branch from the anterior tympanic is shown in through here.
07:45
Here is the stylomastoid branch of the posterior auricular artery
that helps to supply the middle ear.
07:53
We also have the deep auricular branch, and this is a branch of the maxillary artery.
08:00
And the last branch to point out is this branch in through here.
08:05
This is the mallear branch and it is from the anterior tympanic artery.
08:11
Innervation of the middle ear is shown in through here.
08:16
Again, we're looking at the promontory.
08:18
And the two main nerves that we need to be focused about would be the tympanic nerve.
08:26
We see it coming into play here.
08:28
This is a branch from the glossopharyngeal nerve, cranial nerve number nine.
08:34
It branches into anterior and posterior tympanic nerves. It also receives contributions.
08:40
The plexus receives contributions from branches from the internal carotid plexus.
08:46
These are sympathetic fibers.
08:49
And then, leaving the plexus, the tympanic plexus, is the lesser petrosal nerve.
08:56
This conveys parasympathetic fibers to the parotid gland.