Vestibular system Flashcards
What is labyrinth of inner ear composed of?
Cochlea
Vestibule
semicircular canals
What does vestibular system function in?
Maintenance of posture, muscle tone, and eye position with respect to head motion.
Where are vestibular nuclei located?
In lateral aspect of floor of medullary and pontine part of 4th ventricle - underlying vestibular area
Where do axons from vestibular nuclei project to?
Flocculonodular lobe and fastigial nucleus of cerebellum
Spinal cord in VST
Brain stem nuclei of CN III, IV, and VI bilaterally via MLF
Fibers from vestibular nuclei ascend to ventral posterior thalami’s nucelus and to other parietal association areas of cortex
What is internuclear opthalmoplegia?
Failure of CN III, IV, and VI to carry out synchronous horizontal gaze due to MLF lesion.
What is barany chair vestibular exam?
Rotate 10x in 20 seconds where pt flexes forward 30 degrees and rotation stops abruptly. Intact system produces nystagmus opposite of rotation.
what is caloric testing vestibular exam?
Warm or cold water in external acoustic meatus. Cold = nystagmus to opposite side of irrigation.
Warm water= nystagmus to same side in intact vestibular system
What does vestibule of inner ear labyrinth composed of?
Utricle
Saccule
What is vestibular system subdivided into?
Static labyrinth and kinetic labyrinth
What is kinetic labrynith composed of?
Semicircular canals
Crista ampullaris
Cupula
What do semicircular canals do in the kinetic labrynith?
Orthogonally oriented to detect all possible directions of motion.
What are the crista ampullaris?
The specialized hair cells in the semicircular canals in the ampullae
What is the cupula?
Gelatinous mass that the hair cells in the crista ampullaris are embedded in
What do the utricle and saccule do in the static labrynith?
Detect static orientation of head with respect to gravity.
What are the specialized hair cells in the static labrynith called?
Macula utricle and macula succuli
What are hair cells in maculae embedded in?
A gelatinous mass, the otolithic membrane which contains. CaCO3 crystals
What are symptoms of vestibular lesions?
Vertigo, nystagmus, and dysequlibrium.
Central lesions may produce what?
Nystagmus in various directions in absence of vertigo during positional testing
Peripheral lesion causes what?
Horizontal nystagmus only in prescence of vertigo
What is an acoustic neuroma or schwannoma?
A relatively common benign slow growing Schwann cell tumor of vestibular nerve. Typically found in region of internal acoustic meatus or cerebellopontine angle.
Can affect facial and trigeminal nerves.
What is Ménière’s disease?
Vestibular symptoms such as equilibrium loss, nystagmus and vertigo accompany progressive loss of hearing and tinnitus. Onsets 20-30 years of age
What causes hair cell depolarization?
Potassium influx
What happens when microvilli bend toward kinocilium?
The cell will depolarize
When the microvilli move away what happens to the cell?
The cell will hyperpolarize
Describe hair cells
Have microvilli on one end with a longer kinocilium on the opposite end
