The vestibular system

Question 1

What medical term is used to describe instability?

Answer 1

Vestibular ataxia

Question 2

What is the vestibulospinal reflex?

Answer 2

Reflex balance reaction to sudden instability of gait/ posture

Question 3

What is the vestibulo-ocular reflex?

Answer 3

Reflex that preserves visual acuity during head-movement

Question 4

Recall the vestibular system nerve supply of the extraocular muscles

Answer 4

Superior and medial vestibular neurons

Question 5

Recall the pathway of the vestibulo-ocular reflex

Answer 5

Abducens nerve: abduction of one eye
CNVI excites contralateral oculomotor nucleus
Other eye adducted

Question 6

Other than the vestibulo-spinal and vestibulo-ocular reflexes, name 3 functions of the vestibular system

Answer 6

• BP and HR control during rapid up/down tilts
• Synchronises respiration with body orientation
• Provoke motion sickness

Question 7

What are the 2 principle components of the vestibular system?

Answer 7

Otolith organs

Semi-circular canals

Question 8

What is sensed by the otolith organs?

Answer 8

1. Acceleration of head

2. Strength + direction of gravity

Question 9

What are the main components of the otolith organs?

Answer 9

Otolith hair cells
Saccule
Utricle

Question 10

What is the saccule?

Answer 10

Bed of hair cells in inner ear

Question 11

What is detected by the saccule?

Answer 11

Linear accelerations and head tilts in VERTICAL plane

Question 12

What overlays the otolith hair cells?

Answer 12

Otoconia

Question 13

Describe the cilia found on otolith hair cells

Answer 13

Each hair cell has one kinocilia and many stereocilia

Question 14

Describe the directional sensitivity of otolith hair cells

Answer 14

All combinations of lateral and antero-posterior directions

Question 15

What stimulates the otolith hair cells?

Answer 15

Internal resistance of the otoconia to head acceleration

Question 16

Describe the orientation of the utricle and the cells within it

Answer 16

Oriented horizontally with hair cells projecting vertically

Question 17

What is sensed by the semi-circular canals?

Answer 17

Angular rotation of head

Question 18

From where do hair cells project in the semi-circular canals?

Answer 18

Ampullae

Question 19

Describe how the semicircular canals differentiate acceleration and deceleration

Answer 19

Acceleration to the right stimulates canals on the right whilst deceleration to the right stimulates canals to the left, and vice versa

Question 20

How do semi-circular canals ensure a balance of firing when the head is upright?

Answer 20

Fire at tonic firing rate

Question 21

What are the semi-circular canals stimulated by?

Answer 21

Rotation in their own plane

Question 22

What gives signal to the brain of linear acceleration in all 3D directions overall?

Answer 22

Vector sum of utricular and saccular patterns

Question 23

Define vertigo

Answer 23

False perception of movement in space

Question 24

Recall the normal neural pathway of vestibular projections

Answer 24

–> hypothalamus –> spatial cortex

Question 25

Where is the spatial cortex?

Answer 25

Tempero-parietal region

Question 26

Define oscillopsia

Answer 26

Inability to stabilise eyes during head movement in bilateral vestibular legion

Question 27

Describe the main symptom of oscillopsia

Answer 27

Objects in visual field appear to oscillate

Question 28

What is the main consequence of unilateral loss of vestibular function?

Answer 28

Severe nausea and vomiting

Question 29

What medical term is given for an inability to stabilise the eyes?

Answer 29

Vestibular nystagmus

Question 30

What causes vestibular nystagmus

Answer 30

One intact canal has an unopposed tonus

Question 31

Describe the onset of visual nystagmus

Answer 31

Intact canal has an unopposed tonus --> eyes therefore driven to SIDE OF LESION as normal vestibulo-occular reflex o Drifting movement is detected by the brainstem  intermittent “resetting” of eye position with fast saccades  rapid involuntary eye movement

Question 32

Describe the onset of vertigo

Answer 32

• Tonus of the intact canal = signal that head is rotating to intact side - causes feeling of intense spinning

Question 33

Recall 2 symptoms of a bilateral vestibular lesion

Answer 33

Oscillopsia | Mild gait ataxia