Vestibular systems

Question 1

What is the main role of the vestibular system?

Answer 1

Maintaining balance, posture and spatial orientation

Question 2

What are the 3 receptor systems that the vestibular systems works through?

Answer 2

1. eyes
2. general proprioceptive (muscle, joints + tendons)
3. vestibular receptors (ear)

Question 3

State what types of sensation are felt via the spinothalamic tract and dorsal columns.

Answer 3

STT (basic sensation) = crude touch, pain + temp 
Dorsal columns (complex senstion) = vibration, proprioception, discriminative touch

Question 4

What is the membranous labyrinth of the ear?

Answer 4

Vestibular part (semicircular canal) 
Auditory part (cochlea)

Question 5

What is endolymph?

Answer 5

Fills the membranous labyrinth

Composition (high K+ and low Na+) forms endocochlear potential

Question 6

What is perilymph?

Answer 6

Within the bony labyrinth surrounding the membranous labyrinth

Question 7

What information does endolymph give is when it moves/shifts?

Answer 7

• when we move our head the endolymphs shifts within the semicircular canals of the ear
• it allows us to know which plane our head is rotating along
• the speed at which the endolymph moves along also gives information about the speed of rotation

Question 8

What is kinocilium?

Answer 8

Special type of cilium on the apex of hair cells located in the sensory epithelium of the inner ear

Question 9

What effect does endolymph have on the kinocilium?

Answer 9

• endolymphs bends the kinocilium
• Can either cause depolarisation or hyperpolarisation which is dependent on the direction of bending
• Depolarisation: release of neurotransmitter (glutamate)
• Hyperpolarisation: stop neurotransmitter release

Question 10

What channel in the kinocilium open in response to movement?

Answer 10

Potassium channels

Question 11

What is the crista ampullaris, what is its function?

Answer 11

It is a sensory organ located at the ampullae of each of the semicircular canals (3 pairs in total)
Function is to sense angular acceleration and deceleration

Question 12

What are the utricular and saccular maculae?

Answer 12

Both are membranous sacs
Utricular = senses horizontal acceleration
Saccular = senses vertical acceleration

contain otoliths - compress the cilia continuously and are responsive to gravitational forces
otolithic organs = utricles and saccules

Question 13

What are the striola?

Answer 13

Curved ridge running through the middle of the macula that orientates the stereocilia

Question 14

What is the position of the kinocilium of the utricles and saccules in relation to the striola?

Answer 14

Kinocilium of the utricles are polarised towards the striola (divides macula into medial and lateral)

Kinocilium of the saccules are polarised away from the striola (divides macula into anterior and posterior)

these work together to create a 3d representation of linear force

Question 15

How do the eyes remain fixed on an object when the head turns, e.g. turns to the RIGHT

Answer 15

the endolymph causes hyperpolarisation on the left
this inhibits the left medial rectus and right lateral rectus

it causes depolarisation on the right, stimulating the right medial rectus and left lateral rectus
therefore the eyes can still move towards the left while the head moves to the right and so remain fixed on an object

Question 16

What is nystagmus?

Answer 16

a form of vestibulo-ocular reflex

combination of initial slow rotation followed by a fast flick back (rapid, accurate eye movements)

Question 17

What are the names given to normal and abnormal nystagmus? How does abnormal nystagmus occur?

Answer 17

Normal = optokinetic (fixation) + rotational nystagmus
Abnormal = spontaneous nystagmus 

Abnormal nystagmus occurs as a result of damage to vestibular apparatus, brainstem or cerebellum

Question 18

Where do they afferents for the superior + medial, and lateral + inferior vestibular nuclei come from?

Answer 18

superior + medial = ampulla of the semi-circular canals

lateral + inferior = maculae of the utricle and sacculae

Question 19

What is kinetosis?

Answer 19

Motion sickness

difference between visually perceived movement and sense of movement

Question 20

What is Meniere’s disease?

Answer 20

Disease of the inner ear that causes episodes of vertigo

Otoliths go into semicircular canals where they are not supposed to be

Question 21

What does BPPV stand for and what is it?

Answer 21

Benign paroxysmal positional vertigo - it is brief episodes of mild to intense vertigo

Question 22

What causes the dizziness experienced in BPPV?

Answer 22

Due to otoconia from the utricles being displaced to the semicircular canals?

Question 23

What tests are there for balance disorders?

Answer 23

Clinical:

1. eye movements
2. caloric testing
3. hallpike manoeuvre

Vestibular testing:

• videonystagmography
• electronystography

Imaging:
- MRI

Question 24

What is the hallpike manoeuvre?

Answer 24

1. lower head to the table and turn to one side
2. watch eyes for nystagmus
3. if pt gets dizzy and exhibits nystagmus –> ear pointed to the floor is the affected ear
4. if nothing happens –> repeated on the other side
5. move back to upright position