Vestibular Flashcards
the labyrinth (inner ear) is composed of…
- cochlea
- vestibule: utricle & saccule
- semicircular canals
what is the fluid of the bony labyrinth called and what is it continuous with?
perilymph (Na rich)
continuous with cerebrospinal fluid
what is the fluid of the membranous labyrinth called?
endolymph (K rich)
the membranous labyrinth communicates with the ____ which absorbs the continuously produced ____
endolymphatic sac
endolymph
what is the purpose of the vestibular system?
helps with maintenance of posture, muscle tone, and eye position with respect to head motion
the vestibular system is subdivided into the ____ and ____
static labyrinth
kinetic labyrinth
the static labyrinth is composed of the ____ and the ____ which function to…
utricle + saccule
detect static orientation of the head with respect to gravity
specialized hair cells in the static labyrinth are called ____ and ____
macula utricle
macula succuli
the hair cells in the maculae are embedded in the ____ which contains ____
otolithic membrane (gelatinous mass)
CaCO3 crystals
The kinetic labyrinth is composed of ____ which detect…
Semicircular canals
Angular acceleration and deceleration
How are semicircular canals oriented and why?
Orthogonally
So they can detect all possible directions of motion
Specialized hair cells in the semicircular canals are in the ____ and are called ____
Ampullae
Crista ampullaris
Hair cells in the crista ampullaris are embedded in the ____
Cupula (gelatinous mass)
transduction in the vestibular system occurs in the same way it does in the ____ system because…
auditory
endolymph is continuous between the 2 systems
what ion flow causes hair cell depolarization in the vestibular system?
potassium influx
when the microvilli bend toward the kinocilium, the cell will ____
depolarize
when the microvilli bend away from the kinocilium, the cell will ____
hyperpolarize
hair cell receptors synapse with dendrites of ____ whose axons form the ____ n
vestibular ganglia or Scarpa’s ganglia
vestibular n
the vestibular nerve enters the brainstem at the ____ lateral to the ____
cerebellopontine angle
facial nerve
where are vestibular nuclei located?
lateral aspect of floor of medullary and pontine part of 4th ventricle, underlying the vestibular area
axons from the vestibular nuclei project to…
- flocculonodular lobe & fastigal nucleus of cerebellum
- spinal cord - vestibulospinal tract
- brainstem nuclei of CN III, IV, & VI bilaterally via medial longitudinal fasciculus (MLF)
- ventral posterior thalamic nucleus -> parietal association areas of cortex
what is internuclear opthalmoplegia?
- failure of CNs III, IV & VI to carryout synchronous horizontal gaze due to lesion of MLF
- seen in MS or vascular disease
- not specific to vestibular disease
how is the vestibular system examined?
Barany chair test
Caloric testing
what is the Barany Chair test?
- rotate 10x in 20sec
- flex forward 30 degrees, rotation stops abruptly
- an intact system produces nystagmus opposite that of the rotation
what is Caloric testing?
- warm or cold water in the external acoustic meatus
- cold water produces nystagmus to the opposite side of irrigation in an intact system
- warm water produces nystagmus to same side in an intact system
symptoms of vestibular lesion
- vertigo
- nystagmus
- dysequillibrium
central vestibular lesion may produce…
nystagmus in various directions in absence of vertigo during positional testing
peripheral vestibular lesion may produce…
horizontal nystagmus only in the presence of vertigo
Meniere’s Disease
- vestibular symptoms accompany progressive loss of hearing and tinnitus
- onset 20-30 years
Acoustic Neuroma (Schwannoma)
- relatively common benign slow growing Schwann cell tumor of vestibular nerve
- typically found in IAM region or cerebellopontine angle
- may also affect CNs VII & V
