Vestibular System

Question 1

What is the function of the vestibular system?

Answer 1

Maintains balance, posture and spatial orientation

Question 2

What are the 3 receptor systems of the vestibular system?

Answer 2

Eyes
General proprioception via muscles/tendons/joints and cutaneous receptors
Vestibular receptors in the ear

Question 3

What is the role of the spinothalamic tract?

Answer 3

Basic sensations:

crude touch, pain and temperature

Question 4

What is the role of the DCML?

Answer 4

Complex sensations:

vibration, conscious proprioception, discriminative touch

Question 5

What is the membranous labyrinth?

Answer 5

Vestibular part (semi-circular canal)
Auditory part (cochlea)

Question 6

What is the endolymph?

Answer 6

Fills the membranous labyrinth

Endocochlear potential formed (positive voltage) due to high potassium and low sodium

Question 7

What is the perilymph?

Answer 7

Within bony labyrinth
Surrounds membranous labyrinth
High sodium low potassium

Question 8

What do the semi-circular canals consist of?

Answer 8

Anterior, lateral and posterior canals

All at right angles to each other

Question 9

How do we know which plane our head rotates in and the strength of this rotation?

Answer 9

The endolymph shifts within the canals

- speed/volume of endolymph movement

Question 10

What are the otolithic organs?

Answer 10

Utriculus

Sacculus

Question 11

What is the role of the kinocilium?

Answer 11

• when endolymph bends kinocilium causing depolarisation or hyperpolarisation
• Kinocilium contains potassium channels that opens in response to movement
• depolarisation: releases neurotransmitter (glutamate) causing excitation
• hyperpolarisation: stop neurotransmitter release

Question 12

Where is the kinocilium?

Answer 12

In the vestibular apparatus arranged in size order with long at the top

Question 13

What happens within the ampulla of the semi-circular ducts?

Answer 13

• crista ampularis
• embedded in gelatinous gel
• senses angular acceleration and deacceleration

Question 14

What happens within the utricular and saccular maculae?

Answer 14

Membranous sacs
Contain otoliths which compress the cilia and respond to gravitational forces
- utricles get polarised towards the striola so it divides the macula into medial and lateral halves
- saccules get polarised away from the striola so it divides macula into anterior and posterior halves

Question 15

What is the striola?

Answer 15

Curved ridge running through middle of sensory epithelium

Question 16

What is the pathway of the vestibular-ocular reflex?

Answer 16

Vestibular nerve afferents -> central vestibular neurons -> extraocular motor neurons -> eye muscles

Question 17

How do eyes stay fixed on an object whilst the head moves right?

Answer 17

• endolymph causes hyperpolarisation on the left inhibiting left medial rectus and right lateral rectus
• depolarisation on the right stimulates right medial rectus and left lateral rectus
• means eyes move towards the left and stay focused on object

Question 18

What is nystagmus?

Answer 18

A form of vestibulo-ocular reflex

• combination of initial slow rotation followed by fast flick back
• rapid and accurate eye movements

Question 19

Is nystagmus normal or abnormal?

Answer 19

Optokinetic (fixation) and rotational nystagmus - normal

Spontaneous nystagmus - abnormal as damage to vestibular apparatus/brainstem/cerebellum

Question 20

Which nerves are responsible for motor control of eye movements?

Answer 20

• CN III
• CN IV (superior oblique)
• CN VI (lateral rectus)

Question 21

What is the central pathway from the vestibular labyrinth?

Answer 21

Afferents from vestibular labyrinth to vestibular nuclei

Question 22

Where are the vestibular nuclei?

Answer 22

Rostral medulla and pons

Question 23

What are the vestibular nuclei?

Answer 23

• superior vestibular and medial vestibular nucleus

- lateral vestibular and inferior vestibular nucleus

Question 24

What are the afferents to the superior vestibular and medial vestibular nucleus?

Answer 24

From the ampulla of the semi-circular canals

Question 25

What are the afferents to the lateral vestibular and inferior vestibular nucleus?

Answer 25

From the maculae of the utricle and saccule

Question 26

What is the ascending vestibular pathway?

Answer 26

Ascending axons of the neurons in superior vestibular nucleus enter medial longitudinal fasciculus

Question 27

How does the vestibular apparatus project to the cerebellum?

Answer 27

Afferents reach flocculonodular lobe: - directly from vestibular apparatus - indirectly from medial and inferior vestibular nuclei

Question 28

How does the cerebellum project to the vestibular apparatus?

Answer 28

Lateral vestibular nucleus receives excitatory and inhibitory signals from the cerebellum

Question 29

What is the role of the innervating ocular muscles?

Answer 29

- superior vestibular nucleus and medial vestibular nucleus travel to the oculomotor and trochlear travel to them along reticular formation

Question 30

What are the vestibulocortical projections?

Answer 30

Superior vestibular and lateral vestibular communicate with the cerebral cortex

Question 31

What are the vestibulospinal projections?

Answer 31

Lateral vestibular nucleus and medial vestibular form: - lateral vestibulospinal tracts (antigravity muscles) from lateral nucleus - medial vestibulospinal tracts (head and neck muscles) from medial nucleus

Question 32

What does equilibrium depend on?

Answer 32

- signals coming from vestibular apparatus (positioning and movements of head must be continuous with those of eyes and body)

Question 33

What are the main 3 vestibular pathologies?

Answer 33

- kinetosis - Meniere's disease - benign paroxysmal positional vertigo

Question 34

What is kinetosis?

Answer 34

motio sickness | - difference between visually perceived movement and sense of movement

Question 35

What is Meniere's disease?

Answer 35

Of inner ear causing vertigo episodes | - otoliths go into semi-circular canals and shouldn't be there

Question 36

What is BPPV?

Answer 36

Benign paroxysmal positional vertigo: | brief episodes of mild to intense vertigo

Question 37

How do you clinically examine balance disorders?

Answer 37

Eye movements Caloric texting hallpike manoeuvre

Question 38

How do you test for balance disorders?

Answer 38

``` Clinical examination vestibular testing (videonystagmography and electronystography) Vestibular imagine (MRI) ```