Vestibular System Flashcards
Draw the vestibular organ
name important structures [5]
semicircular canals utricle saccule endlymphatic duct cochlea
inputs of vestibular system?
Visual , proprioreceptive and vestibular information
Outputs of vestibular system
mainly reflexes : Stable posture and stable gaze
CNS integrates this and generates responses and controls feelings of nausea, vertigo
Where is vestibular organ found?
Posterior area of inner area
What is the function of hair cells in the inner ear?
The inner ear contains hair cells for hearing and balance
Vestibular hair cells
type
arrangement
Kinocillium - 1 relatively long hair
Stereocilia - 50 shorter ones (stereocilia)
The kinocilium is inserted eccentrically on top of the sense cell; the stereocilia are arranged in parallel rows
Where are stereocilia located?
otolith organs?
semicircular canals?
In macula of otolith organs
in ampulla of semicircular canals
where are the otolith organs located?
what are the otolith organs?
vestibule utricule and saccule joined by a conduit [endolymphatic duct] Utricle is superior and is connected to the semicircular canals saccule connects to cochlea
Movement of endolymph causes what?
Cilia allows the cells to depolarise the cell with movement of the endolymph generated by head movem
How are the hair cells arranged in the utricle?
horizontally
How are the hair cells arranged in the saccule?
vertically
what is the makeup of the semicircular canals?
Hair cells in ampulla - crista , cells surrounded by cupula which helps with hair cell movement
rest of canal is liquid high in K+ - ENDOLYMPH
Where do vestibular nuclei have projections to?
4
Spinal cord
Nuclei of the extraocular muscles
Cerebellum
Centres for cardiovascular + respiratory control
where do vestibular afferent information go to?
4 nuclei
medulla
pons
‘Inferior, medial, lateral (Deiter’s) and superior vestibular nuclei. All four nuclei are found beneath the floor of the fourth ventricle in the medulla and pons, lateral to the sulcus limitans’
Vestibular pathways
Inferior nuclei
vestibulo-ocular reflex
oculomotor
vestibulocerebellar reflexes : balance, vestibular reflexes, and eye movements
Vestibular pathways
what are the lateral , medial, inferior nuclei involved in ?
Vestibulospinal reflex
Which vestibular pathway ?
- spatial orientation and self-motion perception
Information sent to superior vestibular nuclei
> Ventroposterior nucleus
> vestibular cortex
Functions of
Vestibular system
To detect and inform about head movements
To keep images fixed in the retina during head movements
Postural control
What causes depolarization in vestibular systems?
Stereocilia moving towards Kinocilium
depolarization
increase in nerve firing
Stereocilia moving away from kinocilium
what occurs next?
Inhibition
Hyperpolarization
= reduction in nerve discharge
What is involved in angular acceleration?
Semicircular canals
Linear acceleration and tilt
which vestibular organs involved?
Otolith
Utricle : horizontal
Saccule : vertical
VOR
keeps images fixed
vestibular nuclei and oculomotor nuclei
Eye movement in opposite direction to head movement
but same velocity and amplitude
VSR
Lateral tract?
motor neurons to limb muscles
In VSR
neck and back muscles communications happen via which tract
medial tract
Postural control, avoidance of falls and compensatory body movement according to the head position.
via vestibular nucleus
Assessment of Vestibular System
\++++ history Posture & Gait Cerebellar function Eye Movements Imaging : CT , MRI Vestibular tests
Caloric test
responsiveness
symmetric : of response L/R ear
lateral semicircular canals alone – it does not assess vertical canal function or otolithic function
Video head impulse test
Detects vestibular neuritis
Detects disorders of the vestibulo-ocular reflex and identifies which ear is affected in cases of peripheral vestibular loss
Vestibular evoked myogenic potential
Repetitive sound stimulus to one ear and then averaging the reaction of the muscle activity in response to each sound click or pulse
certain vestibular organs and associated nerves are intact and functioning normally. Responses in this test are measured from different muscles in the neck and around the eyes
Rotational test
Disorder of inner ear or brain?
Bilateral or unilateral?
Central vestibular disorder causes?
Stroke
MS
Tumour
Peirpheral vestibular disorders
Vestibular neuritis
Benign Paroxysmal Positional Vertigo (BPPV)
Meniere’s disease
Unilateral and Bilateral vestibular hypofunction
Which P. Vestibular Disorder doesn’t affect hearing?
BPPV
What condition involves the endolymph?
Meuniere
- comes in crisis
- Liquid breaks down membrane
- Membrane repairs but problem continue
Doctor I’m Dizzy
important to consider
Not necesarilly vestibular
Consider heart disorders , hypotension , anaemia . hypoglycaemia , gait disorders etc
Recurrent balance disorders?
Menieres
Migraine
Progressive balance disorders?
Schwannoma vestibular (VIIIth nerve) Degenerative conditions (MS)
Intermittent balance disorders?
BPPV
Acute balance disorders?
Vestibular Neuritis (‘labyrinthitis’) Stroke
how do the otolith organ sense ‘where is my head’
have otoconia at top - this is heavier than endolymph and responds to gravity
help with deflection of sterocilia towards kinocilium
potassium influx > Ca2+ influx = glutamate release
why does it make sense that endolymph is high in ___
potassium
endolymph is the fluid in the membranous labyrinth. High in potassium as you need potassium influx for depolarization
