Vestibular System

Question 1

The vestibular system

Answer 1

three main inputs: visual, proprioceptive and vestibular information.

The outputs are mainly reflexes to maintain a stable posture and stable gaze.

Question 2

The vestibular organ

Answer 2

The vestibular organ is in the posterior area of the inner ear
The inner ear contains hair cells for hearing and balance
The utricule and saccule are located in the vestibule and are joined by a conduit. The saccule is also joined to the cochlea
There are three semicircular canals on each ear, anterior, posterior and lateral
The semicircular canals have an ampulla on one side, and they are connected to the utricle.

Question 3

The labyrinth in the skull

Answer 3

Superior projection of right bony labyrinth on base of skull
The location of the vestibular organ draws planes for anterior and posterior canals
These planes determine which structure will be stimulated with a specific head movement.

Question 4

Hair cells

Answer 4

Vestibular hair cells have a kinocilium (the biggest cilium) and stereocilia.
Cilia allows the cells to depolarise the cell with movement of the endolymph generated by head movement

Question 5

Otolith organs

Answer 5

Utricle and saccule are the otolith organs. Their cells are located on the maculae, placed horizontally in the utricle and vertically in the saccule
The maculae contain the hair cells, a gelatinous matrix and the otoliths on top. These otholiths are carbonate crystals that help the deflection of the hairs.

Question 6

Semicircular canals

Answer 6

The hair cells in the canals are located in the ampulla. The rest of the canal only has a liquid high in potassium called endolymph
The ampulla has the crista, where the hair cells are located. The cells are surrounded by the cupula which helps the hair cell movement
The orientation of the canals in the head defines three planes. Anterior and posterior canals form a 90° angle. Lateral canals are horizontal to the other canals.

Question 7

Vestibular nerve and nuclei

Answer 7

Primary afferents end in vestibular nuclei and in the cerebellum.

Vestibular nuclei have projections to:
Spinal cord
Nuclei of the extraocular muscles
Cerebellum
Centres for cardiovascular + respiratory control

Question 8

Vestibular pathways

Answer 8

Vestibulospinal reflexes
Vestibulo-ocular reflex (VOR)
Vestibulocerebellar reflexes

Question 9

Vestibular cortex

Answer 9

Not one specific area. Since many inputs and integrators are involved, many cortical areas participate.

Main processing centre thought to be in the parietal lobe, in the Parieto-Insular Vestibular Cortex (PIVC)

Question 10

Vestibular system functions

Answer 10

To detect and inform about head movements
Postural control
To keep images fixed in the retina during head movements

Question 11

otolith movement

Answer 11

Linear acceleration and tilt

Question 12

Utricule movement

Answer 12

horizontal movement

Question 13

Saccule movement

Answer 13

vertical movement

Question 14

Angular acceleration

Answer 14

Semicircular canals
Cupulla moves and displaces hair cells
Output signal on VIIIth (vestibulcochlear) nerve is velocity

Question 15

Semicircular canals (SCC) pairs

Answer 15

Anterior from one side with posterior of the opposite side

Question 16

Vestibulo-ocular reflex (VOR)

Answer 16

Keeps images fixed in the retina
Connection between vestibular nuclei and oculomotor nuclei
Eye movement in opposite direction to head movement, but same velocity and amplitude

Question 17

Vestibulo Spinal Reflex (VSR)

Answer 17

Motor neurons to limb muscles (lateral tract)
Motor neurons to neck and back muscles (medial tract)
Postural control, avoidance of falls and compensatory body movement according to the head position.

Question 18

Balance disorder

Answer 18

Main symptom is dizziness or vertigo

Question 19

Balance disorders: LOCATION

Answer 19

labyrinth and/or VIII nerve
vestibular neuritis
Benign Paroxysmal Positional Vertigo (BPPV)
Meniere’s disease
Unilateral and Bilateral vestibular hypofunction.

CNS (brainstem/cerebellum)
stroke
MS
tumours

Question 20

Balance disorders: EVOLUTION

Answer 20

Acute - Vestibular Neuritis (‘labyrinthitis’), Stroke

Intermittent - Benign Paroxysmal Positional Vertigo (BPPV)

Recurrent - Meniere’s Disease, Migraine

Progressive - Schwannoma vestibular (VIIIth nerve), Degenerative conditions (MS)

Question 21

BPPV

Answer 21

Otoliths (carbon crystals) from the utricle, detach from the maculae and float around the semi-circular canals.

Otoliths are not supposed to be found in the canals and therefore when these are floating in the canals, will induce a bigger endolymph flow when the head moves (the crystals will carry more liquid) and therefore the movement of the head would be processed by the brain as bigger and faster than it is in reality.

This will cause vertigo attacks every time the head moves quickly, especially when lying down or standing up.

The attacks are short, because these will end when the endolymph settles (usually less than 1 min) but will be recurrent, happening every time the person changes the head position quickly (as said before, very common on lying down or getting up from bed).

When the head is still, usually there are no vertigo symptoms, but some patients can refer feeling a bit unstable or lightheaded when walking (no specific deficit though).

No hearing deficit