Vestibular System Flashcards
The vestibular system includes what three inputs?
visual
proprioceptive
vestibular information
What are the main outputs of the vestibular system?
reflexes to maintain a stable posture and stable gaze
Where is the vestibular organ located?
posterior area of the inner ear
What important structures are located in the vestibule? What are they joined by?
utricle
saccule
joined by a conduit
Name the three semicircular canals on each ear.
anterior
posterior
lateral
What do the semi circular canals have on one side? What are they connected by?
ampulla
utricle
where does the vestibular organ sit in the skull?
superior projection of right bony labyrinth in the temporal bone on the base of the skull
the plane of the anterior semi circular canal meets the plane of the posterior semi circular canal at what angle?
90 degrees
perpendicular
the planes of the anterior + posterior semi circular canals determine what?
which structure will be stimulated with a specific head movement
list types of cilia the vestibular hair cells have
kinocilium (biggest)
stereocilia
function of cilia
allows the cells to depolarise with movement of the endolymph generated by head movement
what is the utricle?
larger of the two fluid-filled cavities forming part of the labyrinth of the inner ear
what is the saccule?
smaller of the two fluid-filled cavities forming part of the labyrinth of the inner ear
list the otolith organs
utricle
saccule
define otolith
each of three small oval calcareous bodies in the inner ear, involved in sensing gravity and movement
where are the cells of the utricle and saccule located?
on the maculae
how are the cells oriented in the utricle?
horizontally
how are the cells oriented in the saccule?
vertically
the maculae contain?
hair cells
gelatinous matrix
otoliths on top
function of otoliths
are carbonate crystals that help the deflection of the hairs
where are the hair cells in the canal located?
ampulla
name the liquid in the canal
endolymph
endolymph is rich in?
potassium
where is the crista?
in the ampulla
what is the crista?
the sensory organ of rotation
function of the crista
sense angular acceleration and deceleration
the hair cells are surrounded by the matrix called?
cupula
do the semi circular canals have otoliths?
no
describe the orientation of the lateral canals to the anterior and posterior canals
horizontal to the other canals
the planes of the anterior and posterior canals meet at 90 degrees
primary afferents to the vestibular organ end in?
vestibular nuclei and in the cerebellum
vestibular nuclei have projections to?
spinal cord
nuclei of the extraocular muscles
cerebellum
centres for cardiovascular + respiratory control
list the four main vestibular nuclei
superior
lateral
medial
inferior
information that travels to the superior and lateral vestibular nuclei then goes to the?
ventroposterior nucleus > vestibular cortex
list reflexes the vestibular system is responsible for
vestibulospinal reflexes (posture) vestibulocerebellar reflexes (coordination/monitoring) vestibulo-ocular reflexes (eye movements in compensation for head movements)
what area is the vestibular cortex in?
not anywhere specific, many inputs and integrators are involved, many cortical areas
where is the main processing centre of the vestibular cortex?
in the parietal lobe
in the parieto-insular vestibular cortex
in terms of processing of sensory information, what are the primary and adaptive processors?
primary > vestibular nuclear complex
adaptive > cerebellum
list the three main functions of the vestibular system
to detect and inform about head movements
postural control
to keep images fixed in the retina during head movements
how many potentials do hair cells have? name them
3: resting, excitation, inhibition
resting potential of the hair cells
basal discharge (neural firing rate) to the nerve
excitation of the hair cells
deflection of the hair cells towards the kinocilium > increased nerve discharge > depolarisation
inhibition of the hair cells
deflection of the hair cells away from the kinocilium > reduced neural firing rate > hyperpolarisation
otolith movement
linear acceleration and tilt (backward and forwards)
the utricle is sensitive to movements in what plane?
horizontal
the saccule is sensitive to movements in what plane?
vertical
the semicircular canals are sensitive to what movement?
angular acceleration
how do the semicircular canals detect movement?
movement moves endolymph > cupulla displacement > displaces hair cells > depolarisation or hyperpolarisation
what is the output signal on the vestibulocochlear (VIII) nerve?
velocity
semicircular canals on both sides of the head work together in what pairs?
both laterals work together
anterior canal from one side works with the posterior canal on the other side (vice versa)
what is the vestibulo-ocular reflex?
helps keep the image fixed in the retina despite head movement (head moves, eyes stay still)
what is the vestibulo-spinal reflex?
postural control
avoidance of falls compensatory body movement according to head position
what nuclei are involved in the vestibulo-ocular reflex?
vestibular
oculomotor
connections from nuclei in vestibulo-spinal reflex?
vestibular nuclei > motor neurons > limb muscles (lateral tract) or neck/back muscles (medial tract)
assessment of the vestibular system
anamnesis (history) posture and gait cerebellar function eye movements symptoms and impact assessment
list vestibular tests
Caloric test
Video head impulse test (vHIT)
Vestibular evoked myogenic potential (VEMP)
Rotational test
imaging used to assess the vestibular system
CT scan
MRI
main symptoms of balance disorders?
dizziness
vertigo
balance disorders can be categorised based on?
location of the affected structure
evolution of signs and symptoms
peripheral vestibular disorders are located where?
labyrinth and/or VIII nerve
central vestibular disorders are located where?
CNS (brainstem/cerebellum)
list examples of conditions leading to central vestibular disorders
stroke
MS
tumours
list examples of conditions leading to peripheral vestibular disorders
vestibular neuritis
Benign Paroxysmal Positional Vertigo (BPPV)
Meniere’s disease
Unilateral and Bilateral vestibular hypofunction
name categories for evolution of signs and symptoms of balance disorders
acute
intermittent
recurrent
progressive
list conditions with an acute evolution
Vestibular Neuritis (‘labyrinthitis’) Stroke
list conditions with an intermittent evolution
Benign Paroxysmal Positional Vertigo (BPPV)
list conditions with a recurrent evolution
Meniere’s Disease
Migraine
list conditions with a progressive evolution
Schwannoma vestibular (VIIIth nerve) Degenerative conditions (MS)
what are other reasons, apart from vestibular dysfunction, for dizziness?
heart disorders presyncopal episodes orthostatic hypotension anaemia hypoglycaemia psychological gait disorders
