Chapter 12: Vestibular

Question 1

What does the vestibular system do?

Answer 1

1. Monitors the position and movement of the head
2. Gives us our sense of balance and equilibrium
3. Helps coordinate movements of the head and eyes
4. Coordinates adjustments to body posture

Question 2

What are the otolith organs?

Answer 2

Utricle, Saccule

Question 3

What do the otolith organs do?

Answer 3

Detect linear acceleration of head
Head tilt

Question 4

What do semicircular canals do?

Answer 4

Sensitive to head rotation
Angular acceleration (change in velocity) of head

Question 5

What carries out sensory function for the vestibular system?

Answer 5

The hair cells

Question 6

Where are the hair cells located?

Answer 6

They are located in the utricle and the saccule and in three juglike swellings called ampullae in the base of the semicircular canals

Question 7

What is the transduction process for hair cell?

Answer 7

Similar to auditory system
Movement of the stereocilia toward the kinocilium opens mechanically gated channels allowing K+ to enter and depolarizes cell.
Then voltage-gated calcium channels open letting Ca2+ in allowing vesicles to form and release the neurotransmitter to the 8th nerve.

Question 8

What direction does the hair cells need to be for depolarization in the ampulla?

Answer 8

Towards the kinocilium and all the hair cells are going the same direction towards the left

Question 9

What direction does the hair cells need to be for depolarization in the sacculus?

Answer 9

Sacculus is divided by the striola
In the posterior the direction of depolarization is upwards from the striola
In the inferior side of the direction of the depolarization is downwards of the striola

Question 10

What direction does the hair cells need to be for depolarization in the utricle?

Answer 10

Utricle is divide by the striola
The hair cells depolarize in the direction of the striola

Question 11

How does the utricle and saccule detect static displacements and linear accelerations?

Answer 11

By the head induced by titling or translational movements of the head

Question 12

What is otocnia?

Answer 12

It is above the gelatinous membrane that the hair cells are in
Make the otolithic membrane heavier than fluids around it

Question 13

What happens when the head tilts?

Answer 13

When head tilts gravity causes otolithic membrane to shift relative to sensory epithelium.
Shearing causes displacement of hair cell bundles and a receptor potential in hair cell.
The response is sustained for the vestibular nerve axon.

Question 14

What happens when you tilt your head backward?

Answer 14

Hair cells depolarize

Question 15

What happens when you tilt your head forward?

Answer 15

Hair cells hyperpolarize

Question 16

What happens during linear accelerations?

Answer 16

The greater mass of the otolithic membrane causes it to temporarily lag behind the sensory epithelium, leading to transient displacement of hair cell bundle
Transient response of vestibular nerve axon

Question 17

What happens when you accelerate forward?

Answer 17

The hair cells move back and depolarize

Question 18

What happens when you decelerate?

Answer 18

The hair cells move forward and hyperpolarize

Question 19

What plane is the utricle concerned with?

Answer 19

Horizontal plane

Question 20

What plane is the saccule concerned with?

Answer 20

Vertical plane

Question 21

What are the polarities for utricle?

Answer 21

Hair cells on opposite sides of the striola have opposing directional polarities.
Depolarizing toward the direction of striola

Question 22

What are the polarities for saccule?

Answer 22

Hair cells on opposite sides of the striola have opposing directional polarities.
Depolarizing away from of striola

Question 23

What is the ampulla?

Answer 23

At the base of each semicircular canal, a bulbous expansion

Question 24

What is the crista?

Answer 24

Is the sensory epithelium that contains the hair cells, in the semicircular canals

Question 25

What is the cupula?

Answer 25

A gelatinous mass that surrounds the hair bundles

Question 26

How does rotational movement effect the semicircular canals?

Answer 26

Endolymph fluid in canals cannot flow through the cupula.
When the head turns, the inertia of the endolymph produces a force across the cupula, moving it away from the direction of head movement and causing a displacement of the hair bundles.

Question 27

What are the polarities for ampulla?

Answer 27

Kinocilia is pointing in the same direction so when cupula moves in the appropriate direction, all the hair cells are depolarized

Question 28

What happens when you rotate your head to the left?

Answer 28

If you rotate your head to the left, the fluid would flow from the right causing it to depolarize in the left canal but hyperpolarize in the right canal (transient response of vestibular nerve axon)
Since head rotation moves the cupula in opposite directions for the two partners, resulting in opposite changes in their firing rates

Question 29

What are three reflexes of the vestibular system?

Answer 29

Maintain equilibrium and gaze during movement
Maintain posture and balance
Maintain muscle tone

Question 30

What is the vestibulo-ocular reflex?

Answer 30

Head rotation activates semicircular canals in inner ear and drives compensatory eye movements to stabilize image of visual world on the retina
Head rotates L
Eyes rotates R
Gaze remains same