00:01
As we move deeper, we
reach the middle ear.
00:06
And this is a small cavity,
also called the tympanic cavity.
00:12
That superiorly has
a small little area
called the epitympanic recess.
00:18
The portion of the middle ear
directly behind the
tympanic membrane,
we call the mesotympanum.
00:27
Superiorly, we would
have the epitympanum
and inferiorly,
the hypo tympanum,
beyond which, we would
have the Eustachian tube or
or pharyngotympanic tube.
00:41
Here's going to be a schematic
representation of the middle ear
to give some idea
of the structures
and relationships
within this cavity.
00:51
We can think of it as having a
roof also called a tegmental wall,
a floor also called
a jugular wall
because of the nearby location
of the internal jugular vein.
01:03
A posterior wall also
called the mastoid wall.
01:07
That has an opening or
aditus to the mastoid antrum.
01:14
It also has a little bony projection
called the pyramidal eminence
that a very tiny muscle called
the stapedius will attach to.
01:22
And this is where
we're going to find
part of that chorda
tympani nerve we mentioned.
01:28
We'll also have an anterior wall
that's going to have an
opening for another tiny muscle
called the tensor tympani.
01:36
As well as that opening for the for
pharyngotympanic or Eustachian tube,
that will lead down
to the nasal pharynx.
01:43
We'll also have the other side for
the opening of the chorda tympani.
01:49
Medially,
we're going to have
our labyrinth wall
which is going
towards our inner ear.
01:56
And we're going to have these
little what we call windows
called the round window
and the oval window
and a little bump in between
called the promontory.
02:06
And that's basically where
we're going to find something
called the cochlea
on the other side.
02:12
We're also going to
find some prominences
for the facial canal or the
facial nerves traveling.
02:17
And for something called the
lateral semicircular canal,
something that's going to be
part of the vestibular apparatus.
02:24
Laterally, because we're looking
from a lateral point of view,
we would put on the
membranous wall,
which is actually the
tympanic membrane.
02:35
Now let's take a look
at the middle ear cavity
as if we were in it
looking medially.
02:39
Essentially towards
the inner ear.
02:44
We would see our
connection to the pharynx,
particularly the nasal pharynx
called the for pharyngotympanic
or auditory or Eustachian tube.
02:54
And we would see a bump
called the promontory
and that bump is
basically where something
called the cochlea would
sit on the other side.
03:04
We would have these
windows as we call them,
called the oval window
and the round window,
which are structures
related to the inner ear.
03:14
We would have that prominence
for the facial canal
through which the
facial nerves traveling.
03:19
And again, prominence is for
these vestibular apparatus
called the lateral
semicircular canal.
03:27
We would also see
part of that muscle
called the tensor tympani,
something that's going to
act on our hearing apparatus.
03:37
If we were in that middle ear
cavity, looking laterally,
what we would see is the backside
of the tympanic membrane.
03:48
We would again see
our Eustachian tube
or pharyngotympanic tube as
well as that tensor tympani
but now we would see those
three middle ear bones,
the malleus, incus and stapes.
04:02
We would also see
a very tiny muscle
called the stapedius muscle.
04:07
In fact, it's the tiniest
skeletal muscle in the human body.
04:12
And together the tensor
tympani and stapedius
act to serve as something like
moderators in the act of hearing
so that very loud sounds
get their amplitude
somewhat modified.
04:23
For example, during chewing,
it keeps the sound of chewing
from being deafening
to our ears.
04:30
Then finally, we would see the
passage of this chorda tympani
behind the tympanic membrane.
04:37
Again, giving this branch of
the facial nerve its name.
04:41
Now let's take a closer look at
those middle ear bones or ossicles.
04:46
We have the malleus,
incus and stapes,
going from external to internal.
04:52
Sometimes you'll
hear their old terms,
hammer, anvil and stirrup.
04:57
Despite being some of the
smallest bones you'll ever see,
they do have several
unique features.
05:03
So the malleus has
a head, a neck,
and various processes and
anterior and a lateral process
and then the long handle.
05:11
Again, something we could see
during an otoscopic examination.
05:16
The incus has a facet for its
interaction with the malleus.
05:21
And in fact, these bones,
as small as they are,
do form true synovial
joints with each other.
05:29
There is then a body
connecting to a long limb
that ends in a
lenticular process
that forms yet another
synovial joint with the stapes,
which is going to end on
our portion of the inner ear
that will help us
perceive sound.
05:47
The stapes will have that
tiny neck connecting the head
to two crura or legs that
will terminate in a base.
05:55
This base is what's
going to connect
to the oval window
of the inner ear.
06:03
Now let's take a look at the
vascular supply to the middle ear.
06:07
Most of which is going
to be coming off of the
maxillary artery coming off
of the external carotid.
06:14
We have the superior branch
of the anterior tympanic,
the chronic tympanic,
the inferior tympanic,
and the superior tympanic.
06:25
From a lateral point of view,
we can again see the
anterior tympanic,
we can see the mallear branch,
we can see the incudal branch
and a branch actually coming from
the posterior auricular artery,
the style of mastoid branch
and finally the deep
auricular branch.
06:44
In terms of innervation,
most of it is going to come
from the tympanic nerve,
which is a branch of cranial nerve
IX or glossopharyngeal nerve.
06:55
It's going to have branches that have
come from the internal carotid plexus
and this tympanic nerve will end
typically in a branch called
the lesser petrosal nerve.