Now we'll take a look at the internal ear.
The internal ear is divided into two major parts.
The first is a bony area that we see in through here,
and then within the bony part,
we have a membranous region,
which is outlined in this lighter blue color.
More details, here we're looking
at the bony part of the inner ear,
and specifically this region here
is referred to as the vestibule,
and the vestibule contains the
oval window and the stapes.
When the ears are oscillating due to
sound waves, we'll be transmitting
through the oval window.
Associated with the vestibule, our orifices, five
of these orifices are from the semicircular canals,
which are these structures in through here.
And the sixth one is from the scala
vestibuli, which we'll take a look at later.
The scala vestibuli is associated with the cochlea.
The semicircular canals were mentioned a
little bit earlier with regards to the orifices
that communicate with the vestibule.
There are three semicircular canals in each ear.
One is the anterior semicircular
canal based on its orientation.
Another is the posterior semicircular canal,
and then this one that loops around here is
going to be the lateral semicircular canal.
This portion of the lateral semicircular
canal is referred to as its bony limb
and then at the base of each of the semicircular
canals, you have an area of dilatation
and that area or dilatation is
the ampulla, ampullae for plural.
And then the last bony part that's
associated with the inner ear is the cochlea.
We see the cochlea and we do see that it has
a snail-like appearance associated with it.
The round window which is shown
here, or the cochlear window
is an area of communication with the middle ear.
The membranous areas are found within the bony parts.
So we're seeing the semicircular ducts again, or
actually the semicircular canal's the bony part,
And in the shaded yellow to orange area, but within
each of those semicircular canals you have ducts,
and those ducts are the membranous
portions of the semicircular canal.
This would be your superior semicircular duct.
This is the posterior semicircular duct, and
then this is your horizontal semicircular duct.
And then within the vestibule
you have two membranous areas,
one of which is the utricule,
and the other is the saccule.
Within the bony cochlea, you have a membranous
cochlear duct, which we see shaded here in blue.
This is specifically looking at the cochlea.
You can see the spiraling nature of the cochlea
and that is referred to as the osseous labyrinth.
Within the osseous labyrinth, you have a spiral
canal, and this is the spiral canal of the cochlea.
Projecting into the spinal canal
is the osseous spiral lamina.
And then at this particular
region we have the modiolus.
This is a cone-shaped central axis of the cochlea.
It consists of spongy bone, and this
is where the cochlea turns and spirals
about 2.75 times around its central axis.
The cochlear nerve and the spiral
ganglion are located inside of this,
and then the cochlear nerve will then
convey impulses from the sensory receptors
for audition coming from the cochlea.
And this is the very large cochlear
nerve that's receiving all these impulses
that are being conveyed as the cochlea turns
or spirals 2.75 times around its central axis.
Now, this single spiral canal is going
to be divided into three partitions
and this division will occur through
the presence of two membranes.
The first membrane is shown in through
here and this is the basilar membrane.
And then right above up we have the
vestibular or Reissner's membrane.
And now we have three partitions
within what was a single canal.
In addition, in this central area or partition,
we have a structure known as the spiral ligament.
The middle region is referred
to as the cochlear duct.
This is also referred to as a scala media
and then the other two scala are shown here.
This is the scala vestibuli and
then the scala tympani, or tympani
and then resting on the basilar membrane gives
a structure called the spiral organ of Corti.
Within these partitions, or scala, we have fluid.
The cochlear duct is filled
with fluid called endolymph.
And then the scala vestibuli and the scala tympani
are going to be filled with a type of lymph too
but its composition is a little
bit different than the endolymph
and because the difference in
composition, this is the perilymph.
And then here we're looking at, again, the inner
ear, looking at the bony portions of the inner ear,
and then the membranous portions here as well.
Here is the vestibular nerve coming from
the vestibular apparatus of the inner ear.
So this would be conveying impulses
related to maintenance of balance.
Here is the cochlear nerve coming from the
cochlea conveying audition impulses centrally.
And then we have the facial nerve that
travels with both of these divisions.
So facial nerve, cranial nerve VII, vestibulo and
the cochlear nerves from the vestibulocochlear nerve,
which is cranial nerve at number eight.