[ST:NB] W06 - Vestibular System

not an obvious sensory system
- discovered latte 19th century
what it does is very understated
- drives motor system
- keeps balance in space
- keeps visual gaze steady
- similar to gyroscope + accelerometer based response
gimbal stabilizer
- an example of a vestibular system outside the human body
- based on gyroscope input
the vestibular response actuates in an unconscious action
- automated response
because of how automated it is compared to the rest of the senses
- it was hidden away from discovery in modern science
but when there is a problem with the vestibular sense, it become extremely obvious and painful,
- workaround is hard compared to debilitations of other senses
- room is spinning, self is spinning, balance derivation
- autonomic feeling of nausea, disrupts gastro-intestinal well-being

vestibular stimulus

head acceleration

this is the starting stimulus for acceleration
- when head is at constant velocity, there is no stimulus to vestibular system
- when head is accelerating, the vestibular system activates

linear acceleration:

“down” towards core of largest gravity
enables sensing gravity
the organs that deals with linear acceleration
- are called the otoconial organs / otoconial masses
- is basically a mass that is pulled “down” by gravity
stimulation for otoconial organs
- gravity
- jumping up
- sprinting forward from a dead stop
- sitting still on earth

rotational acceleration

angular acceleration
- rotating around body, going around in circles in a merry go round
an inner tube in the ear is filled with fluid
- it has a feather like membrane called cupola at one point
  - very light
- F = m•a
  - feather is moved by the fluid in the tube
- feather like membrane not good for gravity, but is good for rotatory acceleration detection

three circularish canals and two planes
- the three canals have fluid
- the planes are suspended in the fluid

collecting info about angular and linear acceleration

semicircular canals - angular acc.
- the fluid with the cupola does angular acceleration detection
- dysfunction leads: vertigo
otoconial masses (otoliths) - linear acc.
- disequilibrium
- the horizontal plane detects horizontal movement
- the vertical plane detects vertical movement

aging

causes loss in “otoconial” mass
- causes mass to be more feather like from stone like
- feather is not a good detector gravity
- reduces gravity detection
- leads to disequilibrium - different from vertigo
  - loss of balance even when sitting still
dizziness may indicate either vertigo and dis-equilibrium
- both are accompanied by

turns the stimulus from canal and otoconial masses to neural energy
it is an ancient system
- hence the most automated
- mosty mature system
sensor is a hair cell
- similar to the hair cells in the cochlea
- they form a lush bundle

bundle-of-vesitbular-sensor-hair-cells

vestibular-cilia

vestibular-cilia-inners

cupole-placement-in-canals

these cilia are located in strategic places
- with respect to the structure of canals
- and point in towards the middle of the head

cilia-activation-direction

the preferred direction is towards the tallest hair cells
when bundle moves away from the tallest cells,
- the membrane potential drops to \( -60mV \) from the \( -40 mV \)

end organ:
- semi-circular canal
- otoconial mass
one head, two ears
- so pairs of the same end organs get the same stimulus
- the stimulus is processed together

canals

there are three on each side
if there is a yaw plane rotation, it affects canals on both sides
whatever happens on one side, the opposite happens on the other side
- so they are yoked pairs
the canals in parallel planes are yoked
- hair cells are located at the receiving end the canals
yoked pairs don’t receive anything but opposite inputs
- they couldn’t both get excited at the same time
- same with inhibition
the “cupole” gets a blood supply of its own
under heavy intoxication
- cupola becomes light and floats up all the canal
- stimulates hair cells at non-normal patterns
- sends signals that makes no sense
  - no physical stimulation causes this pattern of excitation
- happens also when eating something that messes with blood chemistry
  - this is interpreted as eating something really bad
  - and triggers nausea

otoconial masses

there are otoconial masses on either sides
- outside of the three canals
they are centered on all the canals
- and the vestibule that contains the masses
each side has a vertical plane and a horizontal plane
- utriculus: horizontally oriented otoconial mass
both sides yield the same message
- when there is a linear acceleration
there are masses on top of the otoconial masses
- some dynamic and static events of the head give the same signals
- so, the message is not unambiguous
  - eg. tilting the head back gives the same signal as accelerating forward
- leads to vestibular illusions
vision helps disambiguate the confusion generated from the otoconial mass signals
pilots face a confusion when they cannot see
- knowing if they are moving forward or are in the same place
- since they don’t know where the horizon is
- has caused some crashes

otoconial-masses

otoconial mass is made of highly specialized proteins
- they’re made during fetal life
- otoconian masses have no regeneration
the otoconian mass is a bunch of otoconian units
- goo-ed together as a mass
- these comes apart as one grows older
- piece may also fall off when on a particularly extreme roller coaster
if a piece of the otoconial mass came off
- the otoconial deposits tickle the vestibular hair cell
- causes feeling of acceleration even when a person is just sitting down
  - vertigo
  - Benign Paroxysmal Positional Vertigo (BPPV)
- can be reversed by getting the piece to go through the canal back to the goo-held mass
  - with a push forward
with aging, the goo that holds the otoconials together becomes less sticky
- so the mass gets light, and becomes a poor sensor of gravity
- “presby-equilibrium”
the ability to sense angular acceleration will be compromised
- the cupola will start to disintegrate