vestibular function Flashcards
what is the vestibular system?
A sensory system essential in the control of posture and balance.
where is the vestibular system found?
the inner ear
what is the vestibular system composed of?
3 semi circular canals
utricle to which the semi circular canals connect
saccule
what are the utricle and the saccule collectively known as?
otolith organs
what is the function of the otolith organs?
they detect linear acceleration and encode information about the position of the head in the space?
what is the function of the utricle?
back/front head tilt
what is the function of the saccule?
detects vertical movement of the head
what is the function of the semi circular canals?
to detect rotational acceleration
where are the sensory cells of the semi circular canals located>
swellings in the base of the bony canals called ampulla
what is contained within the ampulla?
snesory receptors called cristae
what are cristae composed of?
cupula
what does the cupula respond to?
movement of the endolymph fluid within the canals
what is embedded within the cupula?
cilia of hair cells which synapse directly with the sensory neurons of the vestibular nerve
what do the hair cells detect?
rotational acceleration
what are the two types of cilia of hair cells?
single, large kinocilium
set of progessively smaller stereocilia
what causes an increased discharge of APs in the vestibular nerve?
distortion of the cilia in the direction of the kinocilium
what causes a decreased discharge of APs in the vestibular nerve?
distortion of cilia away from the kinocilium
what is the name for the sensory apparatus of the utricle and saccule?
maculae
what directions are the maculae orientated in each of the otolith organs?
utricle - horizontal place
saccule - vertical plane
where do the cilia of the maccule protrude into?
otolith membrane
what is embedded in the otolith membrane?
CaCO3 crystals called otoliths
where do projections from the vestibular nuclei project to?
ipsilaterally, bilaterally and contra laterally to descending motor pathways
how do vestibular nuclei project to the cerebral cortex?
via the thalamus
what is kinaesthesia?
perception of movement and body position
what is the function of the tonic labyrinthine reflexes?
keep the axis of the head in a constant relationship with the rest of the body
what do the tonic labyrinthine reflexes use information from?
the maculae and neck proprioceptors
what is the function of dynamic righting reflexes?
rapid postural adjustments that are made to stop you falling when you trip
what happens if someone who has dysfunctional vestibular apparatus closes their eyes?
balance is immediately lost (reduced vestibulo ocular reflexes)
what is the static vestibulo-ocular reflex?
when you tilt your head, the eyes intort/extort to compensate, so that over a certain range, the image stays the right way up
what is dynamic vestibular nystagmus?
a series of saccadic eye movements that rotate the eye against the direction of rotation of the head and body so that the original direction of gaze is preserved despite the head rotating
in dynamic vestibular nystagmus, what happens when the eyeball comes to the end of its range of movement?
rapidly flicks back to the zero position (straight ahead)
what is post rotatory nystagmus?
subjects are rotated in a barany chair, if they are rotated to the left, there is left nystagmus. at the end of rotation for about 20 seconds, during deceleration they get a right nystagmus
why do subjects get nystagmus to the opposite side of acceleration at the end of a post rotatory nystagmus test?
endolymph has “caught up” and pushes the cupula to the opposite direction
what is caloric stimulation used to test?
horizontal SSC
what is caloric stimulation?
When the outer ear is washed with either cold or warm fluid, the temperature difference from core 37C, gets through the thin bone and sets up convection currents which affect the endolymph. Warm fluid (44C) causes nystagmus towards affected side, cold (30C) causes nystagmus away from affected side (COWS – Cold Opposite, Warm Same).
what is the medical term for motion sickness?
kinetosis
what can cause kinetosis?
powerful maintained stimulation of the vestibular system
what is vertigo?
the perception of movement in the absence of movement
what can lead to nystagmus at rest?
lesions of the brainstem
what are symptoms of menieres disease?
vertigo
nausea
nystagmus
tinnitus
what is menieres disease associated with?
over production of endolymph causing increased pressure
what is labyrinthitis?
acute interference with normal vestibular function as a result of infection
