Neuro - Vestibular System Flashcards
What are the 3 main inputs for the vestibular system?
→ visual
→ proprioceptive
→ vestibular
What are the main outputs of the vestibular system?
reflexes to maintain stable posture + gaze
What does the CNS do with the inputed info?
CNS integrates info + generates responses
Where is the vestibular organ located?
posterior area of the inner ear
Why does the inner ear contain hair cells?
for balance + hearing
What are the different parts of the vestibular organ?
→ anterior semi-circular canal → lateral semi-circular canal → posterior semi-circular canal → utricle → saccule
What makes up the vestibule?
utricle + saccule, joined by a conduit
What is connected to the semi-circular canals?
connected to the utricle on one side
Has an ampulla on the other side
What is connected to the saccule?
cochlea
What is the labyrinth?
superior bony projection on base of skull near inner ear
Why is the location of the vestibular organ important?
→ draws planes for anterior + posterior canals
→ planes determine which structure is stimulated for each specific head movement
What are the different types of hair on vestibular hair cells?
→ kinocilium (biggest cilium)
→ stereocilia
What is the purpose of the cilia?
allows cells to depolarise the cell with movement of the endolymph generated by head movement
What are the otolith organs?
→ utricle
→ saccule
Where are the cells of the otolith organs located + arranged?
maculae:
→ placed horizontally in utricle
→ placed vertically in saccule
What does the maculae contain?
→ hair cells
→ gelatinous matrix
→ otoliths on top (carbonate crystals that help with deflection of hair cells)
What are the otoliths and what is their purpose?
carbonate crystals that help with deflection of hair
Where are the hair cells located in the semi-circular canals?
crista of the ampulla
What are hair cells aided by in the semi-circular canals?
cupula (helps with hair cell movement)
Where do the primary afferent form the vestibular organ end up?
vestibular nuclei + cerebellum
Where does the vestibular nuclei project to?
→ spinal chord
→ nuclei of the extra-ocular muscles
→ cerebellum
→ centres for cardiovascular + respiratory control
What makes up the vestibular cortex?
→ not one specific area
→ many inputs + integrators are involved = many cortical areas participate
Where is the main processing centre thought to be for the vestibular cortex?
Parieto-Insular vestibular cortex (PIVC)
In the parietal lobe
What are the functions of the vestibular system?
→ to detect + inform about head movements
→ to keep images fixed in the retina during head movement
→ postural control
Why do hair cells have a resting potential?
Has a basal discharge
How do hair cells generate depolarisation? How does this effect nerve discharge?
Hairs move towards kinocilium, generate depolarisation + increase in nerve discharge
How do hair cells generate hyperpolarisation? How does this effect nerve discharge?
Hairs move away from kinocilium, generate hyperpolarisation + decrease in nerve discharge
What is responsible for keeping the head level during linear acceleration + tilt?
otolith organs + movement
What is the utricle responsible for?
horizontal movement
What is the saccule responsible for?
vertical movement
When do the kinocilium bend backwards?
→ head tilt backwards
→ acceleration with no head tilt
When do the kinocilium bend forwards?
→ head tilt forwards
→ decceleration with no head tilt
What is responsible for angular acceleration?
semi-circular canals
How do the semi-circular canals aid with angular acceleration?
cupulla moves + displaces hair cells
What is the output signal from the vestibular nerve during angular acceleration?
velocity
How do the SCCs work?
in pairs according to planes:
→ both lateral on each side
→ anterior from one side works with posterior from other side + vice versa
What are the 2 main vestibular reflexes?
→ VOR (vestibulo-ocular reflex)
→ VSR (vestibulo spinal reflex)
What is the VOR?
→ keeps images fixed in the retina
→ connection between vestibular nuclei + oculomotor nuclei
→ eye movement in opposite direction to head movement but keeps the same velocity + amplitude
What is the VSR?
→ postural control
→ avoidance of falls and compensatory body movement according to the head position
What tract do the motor neurones from the vestibular nuclei to the limb muscles take?
lateral tract
What tract do the motor neurones from the vestibular nuclei to the neck + back muscles take?
medial tract
How do you assess the vestibular system?
→ anamnesis → posture and gait → cerebellar function → eye movements → vestibular tests → imaging, CT scan, MRI → symptoms + impact assessments
What are the various vestibular tests?
→ Caloric test
→ Video head impulse test (vHIT)
→ Vestibular evoked myogenic potential (VEMP)
→ Rotational test
What are the symptoms of balance disorder?
→ dizziness
→ vertigo
How is balance disorder categorized?
→ location of affected structure
→ evolution of signs + symptoms
What are the two different types of balance disorders based on location?
→ peripheral vestibular disorders (labyrinth and/or vestibular nerve affected)
→ central vestibular disorders (CNS : brainstem/cerebellum affected)
What are examples of peripheral vestibular disorders?
→ Vestibular neuritis → Benign Paroxysmal → Positional Vertigo (BPPV) → Meniere’s disease → Unilateral and Bilateral vestibular hypofunction
What are examples of central vestibular disorders?
→ stroke
→ MS
→ tumours
What’s an example of an acute balance disorder?
→ Vestibular Neuritis (‘labyrinthitis’)
→ Stroke
What’s an example of an intermittent balance disorder?
Benign Paroxysmal Positional Vertigo (BPPV)
What’s an example of an recurrent balance disorder?
→ Meniere’s Disease
→ Migraine
What’s an example of an progressive balance disorder?
→ Schwannoma vestibular (VIIIth nerve)
→ Degenerative conditions (MS)
What can dizziness also be a symptom of other conditions or disorders?
→ Heart disorders → Presyncopal episodes → Orthostatic hypotension → Anaemia → Hypoglycaemia → Psychological → Gait disorders
