Vestibular system Flashcards
what are the main inputs to the vestibular system?
visual
proprioceptive
vestibular information
what are the outputs of the vestibular system?
reflexes to maintain stable posture and gaze
where is the vestibular organ?
in the posterior area of inner ear
what is located within the vestibular organ?
utricle and saccule are located in vestibule and joined by a conduit
saccule also joined by cochlea
3 semi-circular canals on each ear (anterior, posterior and lateral)
semi-circular canals have an ampullar on one side and are connected to utricle
what is the projection of the vestibular organ on the base of skull?
superior projection of right bony labyrinth on base of skull
- Location of vestibular organ draws planes for anterior and posterior canals
what do planes for anterior and posterior canal do?
planes determine which structure will be stimulated with a specific head movement
what do vestibular hair cells have?
kinocilium (biggest cilium) and stereocilia
what do kinocilium and stereocilia do?
allow cells to depolarise cell with movement of endolymph generated by head movement
what are the otolith organs?
utricle and saccule
where are the cells located on the otolith organs?
cells located on maculae
horizontally in utricle
vertically in saccule
what do the maculae contain?
hair cells
gelatinous matrix
otoliths on top
what are otoliths?
carbonate crystals that help deflection of the hairs
how are semicircular canals organised?
- Do NOT have otoliths
- Hair cells in canals are in ampulla
- Rest of canal only has liquid high in potassium called endolymph
what does the ampulla contain?
crista where hair cells are located
cells surrounded by cupula which helps hair cell movements
what is the orientation of the canals?
defines 3 planes
anterior and posterior canals for 90 deg angle
lateral canals are horizontal to other canals
where do the primary afferents of vestibular nerve end?
vestibular nuclei and cerebellum
where does the vestibular nuclei have projections to?
- spinal cord
- nuclei of extraocular muscles
- cerebellum
what do hair cells send inputs to?
vestibular nuclei-> vestibular cortex
various reflexes also activated:
- vestibulospinal
- vestibuloocular
- vestibulocerebellar
what is the vestibular cortex?
not one specific area
many cortical areas participate
main processing centre in parietal lobe -> on parieto-insular vestibular cortex (PIVC)
how does sensory input to the vestibular cortex to motor output?
what are the functions of the vestibular system?
- detect and inform about head movements
- keep images fixed in retina during head movements
- postural control
what are the potentials of hair cells?
- 3 potentials
- hair cells have resting potential which have basal discharge to nerve
- hairs moving towards kinocilium= depolarisation
- increase nerve discharge
- hairs moving away from kinocilium = hyperpolarisation
- reduction in nerve discharge
- each ear side works in opposite ways- when head moves on way- one side excitation, other inhibition
what is the function of otolith organs?
- linear acceleration and tilt movements
- utricle: horizontal
- saccule: vertical
how do the semi-circular canals work?
- angular acceleration
- endolymph moves thus cupula displacement and displaces hair cells
- output signal on VIIIth (vestibulocochlear) nerve is velocity
- work in pairs according to planes
- both laterals work together
- anterior from one side work with posterior of other side
what is the vestibulo-ocular reflex? (VOR)
- keep image fixed in retina
- connection between vestibular nuclei and oculomotor nuclei
- eye movement in opposite direction to head movement
- same velocity and amplitude
what is the vestibulospinal reflex? (VSR)
- compensatory reflex when about to lose balance
- motor neurons to limb muscles (lateral tract)
- motor neurons to neck and back muscles (medial tract)
- postural control and compensatory body movement according to the head position
what is the main symptoms of a balance disorder?
- Main symptom is dizziness or vertigo (very common- 25% ENT and neurological referrals)
what is vertigo?
perception of rotation (spining)
what is dizziness?
not necessarily spinning sensation
how can balance disorders be characterised?
based on location of affected structure and evolution of signs and symptoms
what are the different locations for balance disorders?
peripheral vestibular disorders
- labyrinth and/or VIII nerve
- vestibular neuritis
- BPPV
- meniere’s disease
- unilateral and bilateral vestibular hypofunction
central vestibular disorders
- CNS (brainstem/cerebellum)
- stroke
- MS
- tumour
what diseases are seen in different timeframes of balance disorders?
- acute
- vestibular neuritis
- stroke
- intermittent
- BPPV
- recurrent
- meniere’s disease
- migraine
- progressive
- schwannoma vestibular (VIII nere)
- degenerative conditions (MS)
what are some other causes of dizziness?
- Head disorders
- Presyncopal episodes
- Orthostatic hypotension
- Anaemia
- Hypoglycaemia
- Psychologica
- Gait disorder
