Vestibular system

Question 1

What is the vestibular system?

Answer 1

• Senses equilibrium and balance
• Informs other systems about changes in orientation of the body
• Acceleration and deceleration of the head

Question 2

Where are the sensory receptors located?

Answer 2

Within the labyrinth of the inner ear.

Question 3

Via which nerve is sensory afferent information taken from the inner ear?

Answer 3

Vestibulocochlear nerve - CN VIII

Question 4

What is the role of the endolymph fluid?

Answer 4

Found within the membranous labyrinth, it circulates between the spaces as you move and is constantly stimulating sensory organs in different planes to inform the brain where your head is

Question 5

Where are the utricle and saccule found?

Answer 5

Macula - below the 3 semi-circular canals

Question 6

What is the role of the hair cells?

Answer 6

They act as a sensor in vestibular organs as they are in contact with the dendrites of the vestibulocochlear nerve

Question 7

What occurs when the hair cells bend?

Answer 7

There is a change in depolarisation/ hyperpolarisation so action potentials fire more frequently or less frequently

Question 8

What do cristae detect?

Answer 8

Rotatory movement - dynamic balance

- occur during acceleration and deceleration

Question 9

How do otoliths detect tilting of the head?

Answer 9

They are heavy, so tilting causes gravity to drag them, which bends the hair cells, causing a change in CN VIII input

Question 10

Via which 3 nerves do the vestibular organs communicate to the extraocular muscles about orientation of our eyes and head?

Answer 10

III - occulomotor
IV - trochlear
VI - abducens

Question 11

What are the 3 major postural reflexes the vestibular system is involved with?

Answer 11

1. Vestibular reflex
2. Tonic neck reflex
3. Righting reflex

Question 12

What does the vestibular reflex detect a change in?

Answer 12

The angle of the head relative to gravity

Question 13

What does the tonic neck reflex detect a change in?

Answer 13

A change in the head:neck angle

Question 14

How does the righting reflex work?

Answer 14

Uses vestibular and tonic neck reflex pathways together, plus skin pressure sensors.
- once head position is fixed relative to gravity, the body adjusts relative to the head

Question 15

Which reflex fixes image on the retina during head rotations?

Answer 15

Vestibulo-ocular reflex

Question 16

What causes motion sickness?

Answer 16

If there is a conflict between visual and vestibular input

Question 17

Damage to which specific anatomical structures could present with signs of vestibular dysfunction?

Answer 17

• The inner ear – cristae, maculae
• Pons, medulla oblongata
• Thalamus

Question 18

What clinical signs might you expect, in an animal with vestibular disease?

Answer 18

Lack of balance, falling to one side (in a circle), nystagmus (flicking of the eyes)

Question 19

In which structure of the inner ear are the cristae ampullaris found?

Answer 19

Semicircular canals

Question 20

Where in the CNS are the vestibular nuclei found?

Answer 20

Medulla oblongata and pons