Vestibular structure and function.
Vestibular system also utilizes hair cells, endolymph.
And they will utilize the same endolymph
that comes from the structures associated
with hearing such as the cochlea.
The different structures that we need to be concern
with here are the three semicircular canals
and the otolith organs.
And the otolith organs are the processes that are
in the base of the semicircular canals.
Vestibular hair cells work a lot like auditory hair cells.
The only difference is that they always
have a resting membrane potential
and a resting discharge of
frequency of action potentials.
So even if they haven’t been
stimulated in one direction or the other,
you will still have a resting discharge.
If you activate them, you’ll get an
increase in resting membrane potential
and you’ll get an increase in the number
of valleys of action potential set to the nerve.
If you then go back down to a basal condition,
you will still have a valley of
action potential sent to the nerve.
If then you hyperpolarize it by bending the opposite
direction, you will slow down those nerve impulses.
So here we have a couple of signals,
it’s always on, and if you tilt in one direction
you get depolarization then
increase valuing the frequency.
And if you tilt in the opposite
direction, you get a hyperpolarization
and a decrease in the frequency of action potentials.
So how can we use these to better understand our
direction sense? And if we are spinning in space?
Our semicircular canals allow us to understand
where are head is in terms of rotation.
Is it still?
Is it rotating to the right or to the left?
Are you spinning?
These are the important items
to have good information about.
How the hair cells work in semicircular canals
is the hair cells are in a small pocket
at the base of each of the semicircular canals
known as an ampulla.
The cupula is a small gelatinous structure
located above the hair cells.
Then you have endolymph that’s
gonna be passing through these.
And as the endolymph deforms the cupula,
it will bend the hair cells.
How do you know which direction
this is going to occur?
If you are having the head rotated in one direction,
the fluid will start moving in that direction.
And as that fluid moves through the
semicircular canals, that is what will bend
or cause the cupula to move
which then bends your hair cells.
You will have some hair cells that are facing
in the direction having its tallest component
in the direction of the fluid flow.
And then you’ll have some who have this
tallest component in the opposite direction.
So you’re always gonna get some signal.
Sometimes you’re gonna get
from the same ampulla structure.
Some hair cells are gonna give you
a positive signal of they’re depolarizing
and some will give you a hyperpolarizing.
This is then summed and you can have a
coordinated response to that particular stimulus.
When the head is rotated in one direction,
the endolymph will be displaced in the direction opposite to that of the rotation,
bending the cupula and hair cells. Once the speed of the head and endolymph are equal,
the cupula will swing back to an upright position.
If the head is suddenly stopped,
the endolymph will continue to move in the direction of rotation,
and the cupula is bent in the direction opposite to acceleration.