Vestibular Systems Flashcards
What are the three main inputs of the vestibular system?
Visual
Proprioceptive (pressure)
Vestibular (organ related from inner ear) Rotation and gravity
What are the main outputs of the vestibular system?
Mainly reflexes
- Ocular reflex (allows stable gaze)
- Postrural control
Needs to be fast
What is the role of the CNS in the vestibular system?
The CNS integrates this information (inputs and outputs) and generates the responses.
Where is the vestibular organ?
inner ear
inner ear contains hair cells for hearing and balance
What comprises the vestibule?
Utricule and Saccule
What are the main features of the vestibular canals?
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
How do the canals sit in the skull?
Anterior and posterior canal form a 90 degree angle
What is the purpose of locating the vestibular organs?
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.
Important to generate the right responses
What are the features of the vestibular hair cells?
have a kinocilium (the biggest cilium) and stereocilia
Specially designed to move with the movement of fluid (endolymph)
What is the function of the cilia?
Cilia allows the cells to depolarise the cell with movement of the endolymph generated by head movement
What are the otolith organs?
Utricle
Saccule
What are the main features of 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?
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.
Where are the hair cells of the canals?
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
NO OTHOLITS
What are the main features of the ampulla?
The ampulla has the crista, where the hair cells are located. The cells are surrounded by the cupula which helps the hair cell movement
Cupula closes the ampulla so that the endolmyph can move the cupula to different sides helping the deflection of the cilia
Describe the semi-circular canal planes
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.
Where do the primary afferent end up?
Primary afferents end in vestibular nuclei and in the cerebellum
Brainstem for reflexes (need to be quick)
What do vestibular nuclei have projections to?
Spinal cord
Nuclei of the extraocular muscles
Cerebellum
Centres for cardiovascular + respiratory control
Summarise the vestibular pathways
Hair cells (vestibular organs) recipe inputs
Info goes to vestibular cortex
Also need vestibulospinal, vestibulocerebellar and vestibulo-ocular reflexes
What comprises the vestibular cortex?
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)
What are the vestibular system functions?
To detect and inform about head movements
To keep images fixed in the retina during head movements
Postural control
How do hair cells potential work?
Hair cells have a resting potential which has a basal discharge to the nerve ((still need to contract muscles to stay still due to gravity)
Hairs moving towards the kinocilium generates depolarization and an increase in nerve discharge. (One ear)
Hairs moving away from the kinocilium generates hyperpolarization and a reduction in nerve discharge.
(The other ear)
What is linear acceleration?
Movement in either the horizontal or vertical plane
Not at an angle
What is responsible for otolith movement?
E.g. Tilt
Otolith movement
Basal discharge
What happens during backward/forward movement?
Hyperpolarisation or Inhibiton so system can make compensatory movement in muscles
What is responsible for horizontal movement?
Utricule
What is responsible for vertical movement?
Saccule
What do the semi-circular canals react to?
Angular acceleration
Cupulla moves and displaces hair cells
Will cause hyper polarisation or inhibition
The signal being sent on the vestibulocochlear nerve is velocity
How do semi circular canals work?
SCC work in pairs according to the planes
- Both laterals
- Anterior from one side with posterior of the opposite side
What are the two vestibular reflexes?
Vestibulo-ocular Reflex
(VOR)
Vestibulo Spinal Reflex
(VSR)
What are the main features of the Vestibulo-ocular reflex (VOR)?
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 (compensatory movement of the eye in reaction to the head movement)
What are the main features of the Vestibulo Spinal Reflex (VSR)?
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.
How do you assess the vestibular system?
Anamnesis (history)
Posture and gait
Cerebellar function
Eye movements
What are the different vestibular test?
Caloric test (stimulate inner ear with diff. temperatures which should generate dizziness)
Video head impulse test (vHIT), cannot test each ear separately. better tolerated and v quick
Vestibular evoked myogenic potential (VEMP) - should see response in neck muscles
Rotational test (needs equipment, chair with torsional motor)
What imaging can be used for the vestibular system?
CT Scan, MRI
What are the main symptoms of balance disorder?
Dizziness or Vertigo
Is balance disorder common?
Very common, 25% of ENT and neurological referrals
How can balance disorder be categorised?
Can be cathegorised based on location of the affected structure and evolution of signs and symptoms.
What must you also bear in mind when assessing vestibular issues?
Symptoms and impact assessment
e.g. if dancer can have profound affect on life and lead to mental health issues etc.
What is Vertigo?
Perception of rotation
Feel like things are spinning
What is dizziness?
Related to Vertigo but no turning
Very vague term
Where do peripheral vestibular disorders occur?
labyrinth and/or VIII nerve
Give example of peripheral disorders
vestibular neuritis (inflammation of vestibular nerve)
Benign Paroxysmal Positional Vertigo (BPPV) abnormal presence of crystals in canals
Meniere’s disease (affects inner ear completely hearing and balance) Increased liquid in inner ear
Unilateral and Bilateral vestibular hypofunction
Where do central vestibular disorders occur?
CNS
Give example of central disorders
Stroke
MS
Tumors
How can we classify balance disorders based in evolution?
Acute (vestibular neuritis)
Recurrent (Meniere’s disease)
Intermittent (BPPV)
Progressive (degenerative diseases, schwannoma)
What problems may patients present with that are not necessarily vestibular?
Heart disorders Presyncopal episodes Orthostatic hypotension Anaemia Hypoglycaemia Psychological Gait disorders
