vestibular systems

Question 1

what is the vestibular system?

Answer 1

The vestibular system includes three main inputs:
visual
proprioceptive
vestibular information

The outputs are mainly reflexes to maintain a stable posture and stable gaze. has to be fast so you dont fall over

The CNS integrates this information and generates the responses.

Question 2

what is the anatomy of the vestibular system?

Answer 2

sits in the petrous part of the temporal bone

input:
eye -visual
semicircular canals- rotation and gravity
feet - pressure

output:
eye - ocular reflex
body - postural control

CNS for coordination
also chemoreceptor trigger zone (nausea)

Question 3

what is the vestibular organ?

Answer 3

The ear is separated into three parts: outer, middle and inner ear (labyrinth)

The vestibular organ is in the posterior area of the inner ear (labyrinth) (cochlea is also in here but its for hearing)

The inner ear contains hair cells (in the vestibules) for hearing and balance

Question 4

what is the structure of the vestibular organ?

Answer 4

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.
they each have ampullas at the end. this is where the hairs are

The semicircular canals have an ampulla on one side, and they are connected to the utricle.

Question 5

what is the labyrinth in the skull?

Answer 5

Superior projection of right bony labyrinth on base of skull

The location of the vestibular organ draws planes for anterior (45 degrees to nose) and posterior (90 degrees to anterior) canals

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

Question 6

what hair cells are present in the vestibular system ?

Answer 6

Vestibular hair cells have a kinocilium (the biggest cilium) (specially designed to move with the endolymph) and stereocilia.

Cilia allows the cells to depolarise the cell with movement of the endolymph generated by head movement

they are present in the utricle, saccule and the three semicircular canals

Question 7

what are otolith organs?

Answer 7

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 8

what are the semicircular canals?

Answer 8

should not have otoliths!

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 cupula closes the apulla, the movement of the endolymph will move it one way or another, helping with deflection of hair cells

Question 9

what are the semicircular canal planes?

Answer 9

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.

basically the hole in the cubes formed by the planes points to each ear. but look up a picture

Question 10

what are the vestibular nerve nuclei?

Answer 10

Primary afferents end in vestibular nuclei (in the brain stem) and in the cerebellum

Vestibular nuclei have projections to:

Spinal cord
Nuclei of the extraocular muscles
Cerebellum
Centres for cardiovascular + respiratory control

Question 11

what are the vestibular pathways?

Answer 11

superior:
Ventroposterior nucleus
Vestibular cortex

lateral:
Ventroposterior nucleus
Vestibular cortex
Vestibulospinal reflexes

medial:
Vestibulospinal reflexes

inferior
Vestibulospinal reflexes
Vestibulo-ocular reflex (VOR)
Eye movements

Question 12

what is the vestibular cortex?

Answer 12

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 13

how does vestibular physiology work?

Answer 13

sensory input:
visual
vestibular
proprioceptive

central processing:
primary processor (vestibular nuclear complex)

adaptive processor (cerebellum)

motor output:
motor neurones->
eye movements
positional movements

Question 14

what are the functions of the vestibular system?

Answer 14

To detect and inform about head movements

Postural control

To keep images fixed in the retina during head movements

Question 15

how do hair cell potentials work?

Answer 15

it has three potentials

Hair cells have a resting potential which has a basal discharge to the nerve. this gives info that the head is not moving

Hairs moving towards the kinocilium (longest hair) generates depolarization and an increase in nerve discharge. (excitation)

Hairs moving away from the kinocilium generates hyperpolarization and a reduction in nerve discharge. (inhibition)

Question 16

when are the otolith organs active?

Answer 16

LINEAR ACCELERATION and tilt: otolith movement
eg. a travellator in an airport
it generates the basal potential

Utricule: horizontal movement

Saccule: vertical movement (eg. a lift) (tilt also)

Question 17

When are the semi circular canals active?

Answer 17

ANGULAR ACCELERATION

Cupulla moves and displaces hair cells

Output signal on VIIIth (vestibulcochlear) nerve is velocity

(on one side of head it will be acceleration, on other it will be decelleration)

SCC work in pairs according to the planes

pairs are either (as they are on the same flat plane):

Both laterals

Anterior from one side with posterior of the opposite side

Question 18

what are vestibular reflexes?

Answer 18

Vestibulo-ocular Reflex
(VOR):
eyes focus on same point (image stays fixed on the retina), while the head moves
(quickest reflex)

Vestibulo Spinal Reflex
(VSR):
balance (eg. standing on one leg, also just walking)

Question 19

what is the Vestibulo-ocular reflex (VOR)?

Answer 19

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 20

what is the Vestibulo Spinal Reflex (VSR)?

Answer 20

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 21

how is the vestibular system assessed?

Answer 21

examine:
Anamnesis (patients account of their medical history)
Posture and gait
Cerebellar function (neurological examination)
Eye movements

Vestibular tests:
Caloric test (stimulate inner ear with different temps, to stimulate an asymmetry in the system. should cause eye movements)
Video head impulse test (vHIT) (both ears and integration)
Vestibular evoked myogenic potential (VEMP) (measures conection between vestibular system and neck) (but absence doesnt necessarily mean abnormal)
Rotational test (needs bigger equipment)

Imaging: CT Scan, MRI

Symptoms and impact (on their life) assessment

Question 22

what is a balance disorder?

Answer 22

Main symptom is dizziness or vertigo

vertigo: feeling of rotation (things spinning around)
dizziness: related to vertigo but not the spinning sensation. way more vague though, people use it in different ways

Very common, 25% of ENT and neurological referrals

Can be categorised based on location of the affected structure and evolution of signs and symptoms.

Question 23

what are the possible locations of balance disorders?

Answer 23

Peripheral vestibular disorders:
labyrinth and/or VIII nerve
much more common

E.g.: vestibular neuritis,
Benign Paroxysmal Positional Vertigo (BPPV) (otoliths in the canals, shouldnt be there)
Meniere’s disease (hearing and balance)
Unilateral and Bilateral vestibular hypofunction.

Central vestibular disorders:
CNS (brainstem/cerebellum)

E.g.: stroke
MS
tumours

Question 24

what are different evolutions of balance disorders?

Answer 24

Acute:
Vestibular Neuritis (‘labyrinthitis’)
Stroke

intermittent:
Benign Paroxysmal Positional Vertigo (BPPV) (only effects when the head is moved) (otoliths that are usually in the utricle and saccule move to the Semi circular canal)

recurrent:
Meniere’s Disease
Migraine

progressive:
Schwannoma vestibular (VIIIth nerve)
Degenerative conditions (MS)

Question 25

if a patient says theyre dizzy, what else could it be?

Answer 25

Not necessarily vestibular:

Heart disorders
Presyncopal episodes
Orthostatic hypotension
Anaemia
Hypoglycaemia
Psychological
Gait disorders