Vestibular System Flashcards
What three inputs make up the vestibular system?
- Visual
- Propioceptive
- vestibular information
What are the outputs within the vestibular system?
Reflexes to maintain stable posture and stable gaze
What is the vestibular organ?
Posterior area of the inner ear which contains hair cells for hearing and balance
Describe the anatomy of the vestibular organ?
Utricule and saccule are located in the vestibule and are joined by a conduit.
The saccule is also joint to the cochlea
There are three semicircular canals on each ear, anterior, posterior and lateral
Describe the anatomy of the semicircular canals?
Have an ampulla on one side and they are connected to the utricle
What is known as the labyrinth in the skull?
Superior projection of right bony labyrinth on the base of the skull
The lcoation of the vestibular organ draws planes for anterior and posterior canals
These planes determine which structure will be simulated with a specific head movement
What is a kinocilium?
The biggest cilium hair cell
What type of hair cells make up vestibular hair cells?
Kinocilia and sterocilia
What does head movement do to hair cells?
Cilia allows cells to depolarise the cell due to the movement of the endolymph generated by the head movement
What are the Otolith organs?
Utricle and saccule are the otolith organs, their cells are located on the maculae, placed horizontally in the utricle and vertically in the saccule
What do the maculae contain?
Hair cells as a gelatinous matrix and the otholiths on top.
These otholiths are carbonate crystals that help the deflection of the hairs
What are the crista?
The ampulla has he crista where the hair cells are located.
The cells are surrrounded by the capula which helps the hair cell movement
Where are the hair cells located in the canals?
In the ampulla
The rest of the canal has a liquid high in potassium called endolymph
Describe the planes of the semi-circular planes?
The orientation of the canals in the head defines three planes
Anterior, posterior ( which form a 90 degree angle )and lateral canal- which is horizontal to the other canals
Where are the vestibular nuclei?
Primary afferents end in vestibular nuclei and in the cerebellum
Where do the vestibular nuclei project to?
Spinal cord
Nuclei of the extraocular muscles
Cerebellum
Centres for cardiovascular + respiratory control
Where is the vestibular cortex?
There is no one specific area since many inputs and integrators are involved
= many cortical areas participate
Where is the main processing centre thought to be?
In the parietal lobe
In parieto-insular vestibular cortex = PIVC
How to hair cells become depolarised?
( has 3 responses, resting excitation and inhibition all which have a discharge/nerve stimulation )
Hair cells have a resting potential which has a basal discharge to the nerve
–> hairs moving towards the kinocilium generates depolarization and an increase in nerve discharge
How does hyperpolarization occur in hair cells?
Hairs moving away from kinocilium generates it. And a reduction in nerve discharge
How is Otolith movement sensed?
It represents linear acceleration and head tilit
In what way Utricule movement sensed?
Horizontal movement
In what way is the saccule movement sensed?
Verticle movement
How is angular acceleration sensed?
(semicircular canals)
Capulla moves and displaces hair cells
Output signal on 8th nerve is of velocity
How do Semicircular canal pairs work?
SCC pairs:
work in accordance to the planes
Both lateral
Anterior on one side and posterior on opposite side
What is the vestibulo-ocular reflex?
Keeps images fixed in the retina
Connection between vestibular nuceli and oculomotor nuclei
Eye movement in opposite direction to head movement, but same velocity and amplitude
What is the vestibulo-spinal reflex?
Motor neurons to limb muscles - lateral tract
Motor neurons to neck and back muscles - medial tract
Controls POSTURAL CONTROL, avoidance of falls and compensatory body movement according to head position
What vestibular tests can be done?
- Caloric test
- Video head impulse test
- Vestibular evoked myogenic potential
- Rotational test
How is the vestibular system assessed?
- Anamnesis
- Posture and gait
- Cerebellar function
- Eye movements
What is balance disorder?
causes:
Dizziness or vertigo
Very common - 25% of ENT referrals
How is balance disorder cathegorised?
Location of the affected structure and evolution of signs and symptoms
What location based balance disorders are there?
Peripheral vestibular disorders
Labyrinth and/or 8th nerve
OR
Central vestibular disorders
CNS, brainstem/cerebellum
What evolution based balance disorders are there?
Acute
Recurrent
Intermittent
Progressive
Give examples of Peripheral vestibular disorders?
- Vestibular neuritis
- Benign paroxysmal positional vertigo BPPV
- Meniere’s disease
- Unilateral and bilateral vestibular hypofunction
Give examples of CNS vestibular disorders?
- Stroke
- MS
- Tumours
Give an example of an acute balance disorders? (2)
Vestibular neuritis
Stroke
Give an example of a recurrent balance disorders? (2)
Meniere’s Disease
Migraine
Give an example of an intermittent balance disorders?
Benign Paroxysmal Positional Vertigo (BPPV)
Give an example of a progressive balance disorders? (2)
Schwannoma vestibular (VIIIth nerve) Degenerative conditions (MS)
What other causes can there be if a px complains of dizzyness?
could be:
- Heart disorders
- Presyncopal episodes
- Orthostatic hypotension
- Anaemia
- Hypoglycaemia
- Psychological
- Gait disorders
