Vestibular system

Question 1

what are the main inputs to the vestibular system?

Answer 1

visual

proprioceptive

vestibular information

Question 2

what are the outputs of the vestibular system?

Answer 2

reflexes to maintain stable posture and gaze

Question 3

where is the vestibular organ?

Answer 3

in the posterior area of inner ear

Question 4

what is located within the vestibular organ?

Answer 4

utricle and saccule are located in vestibule and joined by a conduit

saccule also joined by cochlea

3 semi-circular canals on each ear (anterior, posterior and lateral)

semi-circular canals have an ampullar on one side and are connected to utricle

Question 5

what is the projection of the vestibular organ on the base of skull?

Answer 5

superior projection of right bony labyrinth on base of skull

• Location of vestibular organ draws planes for anterior and posterior canals

Question 6

what do planes for anterior and posterior canal do?

Answer 6

planes determine which structure will be stimulated with a specific head movement

Question 7

what do vestibular hair cells have?

Answer 7

kinocilium (biggest cilium) and stereocilia

Question 8

what do kinocilium and stereocilia do?

Answer 8

allow cells to depolarise cell with movement of endolymph generated by head movement

Question 9

what are the otolith organs?

Answer 9

utricle and saccule

Question 10

where are the cells located on the otolith organs?

Answer 10

cells located on maculae

horizontally in utricle

vertically in saccule

Question 11

what do the maculae contain?

Answer 11

hair cells

gelatinous matrix

otoliths on top

Question 12

what are otoliths?

Answer 12

carbonate crystals that help deflection of the hairs

Question 13

how are semicircular canals organised?

Answer 13

• Do NOT have otoliths
• Hair cells in canals are in ampulla
• Rest of canal only has liquid high in potassium called endolymph

Question 14

what does the ampulla contain?

Answer 14

crista where hair cells are located

cells surrounded by cupula which helps hair cell movements

Question 15

what is the orientation of the canals?

Answer 15

defines 3 planes

anterior and posterior canals for 90 deg angle

lateral canals are horizontal to other canals

Question 16

where do the primary afferents of vestibular nerve end?

Answer 16

vestibular nuclei and cerebellum

Question 17

where does the vestibular nuclei have projections to?

Answer 17

• spinal cord
• nuclei of extraocular muscles
• cerebellum

Question 18

what do hair cells send inputs to?

Answer 18

vestibular nuclei-> vestibular cortex

various reflexes also activated:

• vestibulospinal
• vestibuloocular
• vestibulocerebellar

Question 19

what is the vestibular cortex?

Answer 19

not one specific area

many cortical areas participate

main processing centre in parietal lobe -> on parieto-insular vestibular cortex (PIVC)

Question 20

how does sensory input to the vestibular cortex to motor output?

Answer 20

Question 21

what are the functions of the vestibular system?

Answer 21

1. detect and inform about head movements
2. keep images fixed in retina during head movements
3. postural control

Question 22

what are the potentials of hair cells?

Answer 22

• 3 potentials
• hair cells have resting potential which have basal discharge to nerve
• hairs moving towards kinocilium= depolarisation
  
  • increase nerve discharge
• hairs moving away from kinocilium = hyperpolarisation
  
  • reduction in nerve discharge
• each ear side works in opposite ways- when head moves on way- one side excitation, other inhibition

Question 23

what is the function of otolith organs?

Answer 23

• linear acceleration and tilt movements
  
  • utricle: horizontal
  • saccule: vertical

Question 24

how do the semi-circular canals work?

Answer 24

• angular acceleration
• endolymph moves thus cupula displacement and displaces hair cells
• output signal on VIIIth (vestibulocochlear) nerve is velocity
• work in pairs according to planes
• both laterals work together
• anterior from one side work with posterior of other side

Question 25

what is the vestibulo-ocular reflex? (VOR)

Answer 25

* keep image fixed in retina * connection between vestibular nuclei and oculomotor nuclei * eye movement in opposite direction to head movement * same velocity and amplitude

Question 26

what is the vestibulospinal reflex? (VSR)

Answer 26

* compensatory reflex when about to lose balance * motor neurons to limb muscles (lateral tract) * motor neurons to neck and back muscles (medial tract) * postural control and compensatory body movement according to the head position

Question 27

what is the main symptoms of a balance disorder?

Answer 27

* Main symptom is dizziness or vertigo (very common- 25% ENT and neurological referrals)

Question 28

what is vertigo?

Answer 28

perception of rotation (spining)

Question 29

what is dizziness?

Answer 29

not necessarily spinning sensation

Question 30

how can balance disorders be characterised?

Answer 30

based on location of affected structure and evolution of signs and symptoms

Question 31

what are the different locations for balance disorders?

Answer 31

peripheral vestibular disorders * labyrinth and/or VIII nerve * vestibular neuritis * BPPV * meniere's disease * unilateral and bilateral vestibular hypofunction central vestibular disorders * CNS (brainstem/cerebellum) * stroke * MS * tumour

Question 32

what diseases are seen in different timeframes of balance disorders?

Answer 32

* acute * vestibular neuritis * stroke * intermittent * BPPV * recurrent​ * meniere's disease * migraine * progressive * schwannoma vestibular (VIII nere) * degenerative conditions (MS)

Question 33

what are some other causes of dizziness?

Answer 33

* Head disorders * Presyncopal episodes * Orthostatic hypotension * Anaemia * Hypoglycaemia * Psychologica * Gait disorder