Here are two diagrams
representing the structure
of the inner ear. On the left-hand side, you
have what we named, the bony labyrinth. It's
the bony portion of the ear embedded in the
temporal bone. Inside that bony labyrinth
is going to be perilymph fluid. And I'll come back
to that diagram in a moment. On the right-hand
side, you have the membranous labyrinth. And that
membranous labyrinth is filled with endolymph.
Now, what I want you to do is place that membranous
labyrinth inside the bony labyrinths.
And that's exactly what the structure, the anatomical
structure of the inner ear looks like.
Two components, the bony labyrinth filled with
perilymph, and embedded in there, you have
the membranous labyrinth filled with endolymph.
Let's turn back to the bony labyrinth and
let me point out a few anatomical components.
First of all, you have the vestibule in the
center. You can see the oval window and the
round window. That vestibule contains the
recess for the utricle and the saccule. The
utricle and the saccule is one of the anatomical
components of the inner ear that houses the
receptors for movement of the head, linear
movement of the head and the position of the
head. They house the macula, and I'll talk
about those later on in this lecture. On
the left-hand side, you see the semicircular
canals. They are at right angles to each other.
There are three of them there. Those semicircular
canals, as they approach the vestibule, have
a dilated portion we call the ampulla.
It's in the ampulla that we have special structures
called cristae. And those cristae house the
receptors for turning the head, moving the
head at an angle, and I'll talk about those
also in this lecture. Now, the
third anatomical component of the
inner ear is the cochlea, shown here. The
cochlea is a spiral-shaped organ. It spirals
about two and three-quarter turns. And down
the centre core of the spiral is a bone called
the modiolus bone. And right in that bone
is the spiral ganglia. The spiral ganglion
houses the nerve cell bodies, the neurons,
the bipolar neurons that are going to send
fibres to the hair cells in the cochlea and
transmit information back into the central
nervous system that give us the
sensation of sound.
This is another diagram to explain what I
mentioned in the previous slide. In fact,
this shows you the membranous labyrinth and
just a little bit more detail that I'll
briefly summarize here. Focus on label 1 there.
That's the vestibule. It's a vestibule
of the membranous labyrinth, which the membrane
is enclosed or encloses endolymph. You can
see the macula sacculi and the macula utriculi.
And those two maculae contain sensory receptors
for the position of the head and linear movement.
Two there, labelled, shows you the semicircular
canals, and a little illustration at the top, just
reminding you that this membranous labyrinth
is enclosed in the osseous labyrinth
and surrounded by perilymph.
As I explained, each of those semicircular
canals has a dilation called the ampulla.
And within each of those ampulla are the crista,
crista ampullaris. They have their receptors that
respond to the angular movement or tilting
of the head. So there are three of these.
Three of these and two maculae, and then finally,
the organ of Corti, the cochlea duct create
the six sensory regions of the inner ear. The
organ of Corti is going to be in the cochlea
duct within the cochlea, and that's going
to be responsible for sending sensations back
to the central nervous system about sound.