In this video I want to look at structures of the inner ear.
The inner ear has structures both for conversion of sound vibrations in the air to nerve impulses,
and also the vestibular system, our system of balance.
So we can see on this model the area that looks somewhat like a rolled up snail shell.
This is known as the cochlea.
And the cochlea is three tubes that we will talk about it a different video, that are
coiled around roughly 2 1/2 times.
Within the cochlea we will find the functional organ, or organs, of hearing, the organs of
Corti.
We will look at those in another video.
Between the cochlea and these large semi circles we have the area known as the vestibule.
And the vestibule, as its name implies, is associated with the vestibular system.
Within the vestibule we can see two sacs, here gray sacs, we cut it open so you could
take a look inside.
The top sac is the utricle, and the bottom is the saccule.
Utricle and saccule contain mechanisms for detecting linear motion, or acceleration and
deceleration.
The utricle and the saccule are filled with a fluid called endolymph.
The remaining structures here are known as the semicircular canals.
As you can see there are three semicircular canals in each ear.
And the semicircular canals are designed to help us detect rotational motion or angular
motion.
They are filled also with a fluid, and here we have cut them open to represent the gray
area, they are filled with fluid known as endolymph.
And at the end of each semicircular canal there's a widened area, you can see here and
here, these are known as the ampulla.
The ampulla is where we actually detect the motion of the endolymph within the semicircular
canals.
Notice the three semicircular canals for each major plane of the body.
There is one for a transverse plane, one for a sagittal plane, and one for a coronal plane,
of the body.
The three semicircular canals.
Now on this model here we see what is known as the endolymphatic sac.
And it has a duct taking the endolymph down into the utricle and the saccule.
It should be poised up here but the model manufacturer made it a looser plastic so it
doesn't stay where it belongs.
So the endolymphatic sac.
Now if we look inside this model, I'm going remove a portion of the cochlea, and we can
see down inside the cochlea, we can see the three different areas within the cochlea.
The pink represents our scala vestibuli, the green represents our scala tympani.
And the blue represents our cochlear duct.
We will see those in another video in a much higher magnification.
Associated with the cochlear duct, the scala tympani, and the scala vestibuli, we are going
to have the cochlear system for conversion of vibrations into nerve impulses.
And the scala vestibuli begins here at a structure known as the oval window.
The stapes, one of the ossicles of the ear, will vibrate against this oval window, the
beginning of our scala vestibuli.
At the end of our scala tympani we have another window, this is called the round window, and
the round window releases any vibrations back into the middle ear chamber, so they will
not echo back into the cochlear system and be heard as an echo.
Now if I rotate this around so that we look at it from a slightly reverse angle, if we
put this back together, and take a close look at it, we can see the nerves coming from the
organs of Corti forming the cochlear portion of cranial nerve number eight, the vestibulocochlear
nerve.
And we also see the nerves coming out of the utricle and the saccule, forming the vestibular
portion of the vestibulocochlear nerve.
So just a reverse angle of the cochlea, where you can see the cochlear portion of cranial
nerve number eight, and the utricle and saccule with their vestibular portion of cranial nerve
number eight.