Vestibular System Flashcards
What are the 3 main inputs of the vestibular system?
Visual
Proprioceptive
Vestibular info
What are the main outputs of the vestibular system?
Reflexes that allow you to be maintain stable posture, gaze and stop you from falling over:
Ocular reflex
Postural control
Where is the vestibular organ found?
Posterior area of inner ear
What does the vestibular organ do?
Senses rotation and movement of the head
How many semicircular canals are there and describe them
There are 3: anterior, posterior and lateral
They have an ampulla on one side and are connected to the utricle
They do not have otoliths
What is the biggest cilium on vestibular hair cells called?
Kinocilium
Where are hair cells in the vestibular cells found?
On all 5 organs:
utricle
saccule
lateral, posterior and anterior semicircular canals
How do the cilia on hair cells allow depolarisation?
They are moved by endolymph when the head moves
What are the otolith organs? Where are their cells located?
Utricle and saccule
Their cells are located on the maculae
What are otolith?
Carbonate crystals on top of the hair cells that helps their deflection
How are cells placed in the utricle?
Horizontally
How are cells placed in the saccule?
Vertically
How is the macula structured?
Contains hair cells, a gelatinous matrix and the otoliths on top
In the semicircular canals where is the hair located?
On the crista in the ampulla
What are the 3 planes in the semicircular canals?
Anterior and posterior (that form a 90 degree angle)
Lateral which are horizontal to the others
Where do primary afferents end?
Vestibular nuclei (in brainstem) and cerebellum
What do the vestibular nuclei have projections to?
Spinal cord
Nuclei of the extraocular muscles (eye movements)
Cerebellum (to get feedback)
Centres for cardiovascular + respiratory control
What is the role of the vestibular cortex? (3)
To detect and inform about head movements
To keep images fixed in the retina during head movements
Postural control
How many potentials do hair cells have?
Resting
Excitation
Inhibition
Describe the resting potential of hair cells
Has a basal discharge to the nerve
What happens to nerve discharge during excitation?
Increases
When do hairs move towards to kinocilium?
During excitation: depolarisation of cell
When do hairs move away from the kinocilium
During inhibition: hyperpolarization of cell
What type of movement do otolith organs detect?
Linear acceleration and tilt
Out of the utricle and saccule, which is sensitive to horizontal movement and which to vertical movement?
Utricle: horizontal movement
Saccule: vertical movement
What movement do semicircular canals detect?
Angular acceleration
How do semicircular canals work?
In pairs- anterior from one side will work with posterior from other side
Cupulla moves and displaces hair cells (capulla surrounds hair cells)
Output signal on vestibulocochlear nerve is velocity
What does the vestibulo-ocular reflex do?
Keeps images fixed in the retina when you move your head
Eyes move in the opposite direction to head movement but at same velocity and amplitude
Connection between vestibular nuclei and ocular nuclei
What does the vestibulo spinal reflex do?
If moving and about to loose balance it stops you from falling by causing certain muscles to contract
Where do motor neurons of the lateral vs medial tract go to in terms of the vestibulospinal reflex?
Lateral= go to limb muscles Medial= go to neck and back muscles
What is assessed in a vestibular system assessment?
Anamnesis (history) Posture and gait Cerebellar function Eye movements Vestibular tests
What is the main symptom of balance disorder?
Dizziness or vertigo
Vertigo is spinning but dizziness is a subjective term
What do peripheral vestibular disorders affect?
Labyrinth or CN VIII
What do central vestibular disorders affect?
CNS: Brainstem or cerebellum
What are the main acute vestibular disorders?
Vestibular Neuritis (‘labyrinthitis’), stroke
What is the main intermittent vestibular disorder?
Benign Paroxysmal Positional Vertigo (BPPV)
What are the main recurrent vestibular disorders?
Meniere’s Disease (hearing loss will be in one ear), Migraine
What are the main progressive vestibular disorders?
Schwannoma vestibular (VIIIth nerve), Degenerative conditions (MS)
What else may dizziness indicate other than vestibular disorders?
Heart disorders Presyncopal episodes Orthostatic hypotension Anaemia Hypoglycaemia Psychological Gait disorders
How is hearing loss characteristic in Menieres?
Only occurs in one ear
What is the vestibular cortex?
It’s not one specific area since many inputs and integrators are involved- many cortical areas participate
Where is the main processing centre of the vestibular cortex?
In the parietal lobe in the parieto-insular vestibular cortex
What vestibular tests can be carried out?
Caloric test
Video head impulse test
Vestibular evoked myogenic potential (measures connections between vestibular system and neck muscles)
Rotation test
What imaging techniques can be used to assess the vestibular system?
CT, MRI
