Lecture 18

Question 1

What is the point of the vestibular system?

Answer 1

Answers two basic questions:
 - "Which way is up?"
 - "Where am I going?"
Contributes to 
- Keeping our eyes still as we move
 - Maintaining our upright posture
 - Our ability to perceive our own movement within space

Question 2

What does the orolith organs control?

Answer 2

Linear motion

- forward or backward

Question 3

What does the utricle sense?

Answer 3

Horizontal (feeling of acceleration in car)

Question 4

What does the saccule sense?

Answer 4

Vertical (feeling of moving upward in elevator)

Question 5

What does the semi-circular canals sense?

Answer 5

Head rotation
Horizontal (spinning)
Anterior vertical and posterior vertical act antagonistically to each other depending on the direction of rotation

Question 6

What is the ampulla?

Answer 6

Sensory structures

Signals lead to vestibular nuclei in brain cell

Question 7

What is the vestibular labyrinth filed with?

Answer 7

Endolymph

Question 8

What are the hair cells of the vestibular system?

Answer 8

Sensory receptors of the vestibular system

• Found in all of ampulla, utricle and saccula
• Lip links causes opening of channel in hair bundles to let K in endolymph
• Same principle as hair cells of the auditory system but they respond to lower frequencies (0-20Hz)

Question 9

How is the vestibular hair bundle structurally different from auditory hair cells?

Answer 9

Vestibular saccular hair cell

• vestibular hair cells keep their kinocilium throughout life
• Kinocilium is a true cilium unlike stereocilium
• Bundling of cilia make it better to transmit low frequency stimuli

Question 10

What are the two types of vestibular hair cells?

Answer 10

saccule and utricle (detect head tilt and acceleration)

Question 11

Where are hair cells found?

Answer 11

In a sensory patch called the macula

Question 12

What do the hair cells project onto?

Answer 12

Gelatinous otolithic membrane

Question 13

Which is denser, the otonocia or the gelatinous otolithic membrane?

Answer 13

otoconia

Question 14

Does the otoconia respond to gravity differently from the gelatinous otolithic membrane?

Answer 14

yes

Question 15

How does the otoconia move?

Answer 15

Moves downward and drags membrane and hair bundles down

- selective inhibition and activation of hair cells

Question 16

How can the vestibular input to the CNS be ambiguous?

Answer 16

Information from the utricle and the saccule must be integrated with that from visual or somatosensory systems

Question 17

How does gravity affect the vestibular system?

Answer 17

Otoconia and endolymph are heavier than hair bundles
- moves slower than the rest of the structure where hair cell body is
Endolymph and membrane moves to the left where hair cells move to the right
- confusion
- brain integrates information from different sensory paths
- tilt vs acceleration

Question 18

What is the structure of the cupula?

Answer 18

Gelatinous structure penetrated by hair bundles

Question 19

How does the ampulla control the direction of hair cells?

Answer 19

One side of ampulla makes hair cells orient in one direction while the other side makes them orient in the other direction

Question 20

What does the semicircular canals detect?

Answer 20

Angular acceleration (rotation)

Question 21

How does the semicircular detect rotation?

Answer 21

The inertia of endolymph during rotation displaces the cupula
Endolymph area slower to move than rest of head

Question 22

How does alcohol cause the sensation of rotation?

Answer 22

1. Hair cells on outside of semicircular canal is moving but the hair on the inside does not so it looks like they are moving in the opposite direction
2. Cupula pushes hair bundles in one direction or another
3. Alcohol absorbs into the cupula easily than the endolymph - causes spinning sensation when drunk
4. Alcohol will disperse out of cupula and into endolymph - feels fine
5. Next day - more alcohol in endolymph than cupula - spinning sensation in opposite direction
   Important to drink plenty of water to dilute alcohol

Question 23

How do the semicircular canals work?

Answer 23

In pairs on either side of the head

• Horizontal canals on both sides lie in roughly the same plane so can act as a functional pair
• The anterior canal on one side lies in parallel with the posterior canal on the other side so acts as a functional pair

Question 24

What are the steps of the Vestibulo-ocular reflex?

Answer 24

1. Shake your head while reading
2. Shake the book you are reading from
   - Which is easier?

Question 25

What does the vestibular nystagmus allow?

Answer 25

Resetting of eye position during sustained head rotation

Question 26

What happens when the subject is seated and rotated towards the right at a constant rate in the dark?

Answer 26

Slow phase: Eyes rotate in the opposite direction to head movement
Fast phase: Rapid resetting movement back to the center of the gaze
- Right quick phase movement = right beating nystagmus

Question 27

How does eye flicking keep up with rotation?

Answer 27

Up - leftwards
Down - Rightwards
Rotating right - eyes move to the left
Slow phase and fast phase = nystagmus
“nod”
- stops after a while as endolymphs manage to catch up to the rotation
- Left quick phase movement = left beating nystagmus

Question 28

What is Meniere’s Disease?

Answer 28

Poorly understood, spontaneous condition

• No definitive cause
• Potentially due to excessive endolymph

Question 29

What are symptoms of Meniere’s Disease?

Answer 29

Intermittent, relapsing vertigo (spinning feeling)
- Vertigo happens with no apparent reason
- Vertigo can typically last 2-3 hours but in severe cases can last 2-3 days
- removal of vestibular system
Can be accompanied by tinnitus and distorted hearing

Question 30

What are treatments for Meniere’s Disease?

Answer 30

diuretics, sedatives, steroids
Extreme treatment: remove the labyrinth or destroy vestibular hair cells
- Hair cell removal
- - aminoglycosides e.g. gentomyosin
- - -antibiotic
- - - prevents K from going into endolymph
- - - apply antibiotic to vestibular labyrinth
- - -risky as it can affect cochlea so concentration is important