L30 Vestibular system Flashcards
What are hair cells?
receptor cells of the vestibular and cochlear division of the inner ear
what are the hair cells responsible for?
transducing mechanical stimuli into neuronal stimuli onto the afferent fibers of CN 8 Vestibulocochlear n.
what does the apex of hair cells contain?
What are they surrounded by
sterocilia
endolymph
there is a high concentration of ___ in the endolymph which is essential for signal transduction process
K+
Describe the mechanism behind the depolarization/hyperpolarization of hair cells
-mechanical force from endolymph against hair cells will open/close the TRPA-1 channels causing depolarization or hyperpolarization
what is the “tip link”? Explain what happens when the tip link is opened.
they are between the stereocilia of hair cells and they directly open the hatch on top of the TRPA-1 channel causing K+ influx = depolarize the hair cell => opening of calcium-gated channels=> Ca2+ influx = NT release on CN 8 (afferent) causing a full action potential!
what type of potentials do hair cells have
graded potentials
the frequency of AP _____ as the graded potential of the hair cells ___
increase
increase
what are the 2 otopith organs
saccule and utricle
describe the otolith organs (saccule and utricle)
endolymph filled pockets whose walls are lines with hair cells
what do otolith organs detect?
linear acceleration
what is the purpose of the hair cell cilia and kinocilium having alternating oritentations relative to the stiola
allows a single sitmulus to activate one group and inhibit the other group at the same time
what is kinocilium?
the largest cilium
what happens if the cilia are tilted away form the kinocilium
inhibits causing a decrease in NT release and decreasing AP frequency relative to neutral position
what happens if the cilia are tilted towards form the kinocilium
excites causing an increase in NT release and increasing AP frequency relative to neutral position
what are semicircular canals?
endolymph filled pipes whose walls are lined with hair cells
what can semicircular canals detect
angular acceleration
when endolymph move relative to the walls of the canal (like when the head spins) it causes the cilia to bend which deduces?
angular acceleration
what happens to the capula/cilia when hte semicircular canal (and head) rotate to the left?
bend to the right = excitation or inhibition
the endolymph in the semicircular canal is _____
delay - think of water spinning in a bottle, it takes time to reach the speed of the wall of the bottle
the vestibular system works largely at a ____ level, thus there is NO primary vestibular cortex area
subconscious
what is the basic vestibular pathway
- input from vestibular system
- input uses CN 8
- to vestibular nuclei
- output sent to cerebellum, motor neurons of the limbs, back and neck, motor neurons controlling extraocular muscles (important for VOR)
explain the Vestibuloocular reflex?
head rotation to the L
endolymph flow to R
excitation in L - pushed back
inhibition in R - pushed forward
what is nystagmus
alternating smooth pursuit in one direction followed by a saccadic movement in other direction
slow phase - driven by reflex circuitry
fast phase - reset mechanism driven by saccadic circuitry
*physiologica vs. pathological
what is vestibulo-ocular nystagmus
physio nystagmus induced by continous rotation of the endolymph (and head?)
endolymph flow activates VOR
if stimulus is persistant - eyes flips back and forth
what is the slow phase
drive by reflex
when eyes swing in opposite direction of head spin
what is fast phase
driven by saccadic circuitry
eyes reset after reaching max gaze
what is occulocephalic Maneuver (doll’s eye maneuver)
examiner forceibly turns head of pt and looks to see if the COR is intact
should work in comatose pts as well
what is caloric testing of VOR
place cold water in ear of pt which changes the density of the endolymph and induces a spin
cold water - makes endolymph sink = inhibiting that side ( put water in R ear, would cause rxn as if head was spinning to the L) = OPPOSITE
warm water - makes endolymph float, exciting the side (put was in R ear, would cause a rxn as if head was spinning to the R) = SAME
what is Meniere’s disease
abnormalities of the endolymph circulation caused by dilation of the endolymph compartment and degen of hair cells
symptoms - sudden and recurrent vertigo attacks
motions sickness cause
caused by discrepancy between the vestibular and visual inputs
why do you get the spins with alcohol intoxication
alcohol interacts with endolymph and induces abnormal spinning of the endolymph similar to that seen in the caloric testing of the VOR
what is the effect of antibiotics on vestibular system
can be toxic to hair cells - can accumulate in endolymph
describe pathological vestibular nystagmus
cause by damage to one side of the vestibular system (canal OR CN8)
will induce slow phase towards side with damage labyrinth and fast phase toward normally functioning side
will persist as this pathological stimulus also persists
