Case 4 - the Vestibular System Flashcards
what does the vestibular system do
detects forces generated by movement, acting as an accelerometer. translates these into a sense of balance.
provides information about the position of the head in space
allows other CNS structures to rapidly compensate for changes
what is the vestibular system embedded in
bone - membraneous labyrinth
where is the vestibule located
between the semi-circular canals and the cochlea
what does the vestibule contain
the utricle and the saccule
what do the saccule and utricle contain
equilibrium receptors called maculae
what is the saccule continuous with
cochlear duct anteriorly - vertical acceleration = lift
what is the utricle continuous with
the semi-circular ducts posteriorly - horizontal = car
what do the semi circular canals form
the dynamic system and detects angular acceleration
what do the otolith organs form
the static system and detect linear acceleration
what are otoconia
calcium carbonate crystals that form the striola which in turn rests on the otolithic membrane
rely on inertia to function by detecting changes in linear acceleration
where are the hair cells embedded
the gelatinous layer
what are the semi circular canals filled with
endolymph
what is endolymph
high K+ solution with signal transduction occurring in the ampullae
what are the semi circular canals sensitive to
pitch, roll and yaw. essential for coordination of eye movement
what does fluid movement do
displaces a gelatinous mass known as the capula
what does this displacement cause
physical strain on the hair ells
what does physical strain on the hair cells cause
deflection towards the kinocilium icreases firing, deflection away from the kinocilium decreases it
this allows for very rapid detection of changes in angular acceleration of the head
what is the signal transduction done by and what kind of transmission is it
mechanically gated channels and by glutamatergic transmission
what does the vestibule-ocular reflex prevent
retinal slip
head rotates left and eyes rotate right
what is nystagmus
an element of the VOR alternating slow eye movement with rapid saccadic movement
what are the slow phase movements mediated by
vesibulo-ocular pathway
what are the fast phase movements triggered by
cerebral cortex
how to test for nystagmus clinically
introducing warm or cold water into the external auditory meatus. causes convection currents in the endolymph stimulates hair cells as if the head was rotating leading to nystagmus.
what phase is present in a comatose patient
the slow phase but not the fast phase
this is because the cerebral cortex is not functioning but the vestibule-ocular pathway is still functioning
what does dysfunctional slow phase imply
a lesion in the vestibule-ocular pathway
what does the vestibule-spinal tract mediate
basic balance and postural control
how do axons from the vestibular nuclei descend
ipsilaterally
where to the vestibular nuclei sypnace
on lower motor neurones
activity in the vestibular nuclei is modulated in where?
the cerebellum
what does meniere’s disease do
increase in endolymph pressure. we don’t know what causes this increase. disrupts signal transduction and can result in tinnitus, nausea, spontaneous nystagmus
what is benign paroxysmal positional vertigo?
dislodged bits of otolith stimulate the cupola in the posterior SSC causing vertigo. the Epley manoeuvre to nudge them back into the vestibule
what treatment to use for motion sickness etc
anti histamines
