Ch 15: Vestibulo-Ocular Response Flashcards
parts of the inner ear sense head rotations, which include
pitch, roll, and yaw
head translations include
bob, heave, and surge
the purpose of the rotational vestibular-ocular response is to
keep the whole visual world imaged stationary on the retina as best as possible
what detects head rotation and what response does this provide
semicircular canals of the inner ear can provide a sense of head rotation- they provide the rotational vestibule-ocular response
what are head translations and gravity detected by
they are sensed by the otolithic organs of the inner ear
translational vestibule-ocular response caused by? is it important?
produced by otolithic organs of the inner ear
-it isn’t important in humans, but well developed in some animals
T/F: the vestibulo- ocular eye movements are primarily non-visual
True
the labyrinth of the inner ear contains two sensory systems important to eye movement and posture. these are
the semicircular canals and the utricle and saccule
what is the osseous labyrinth
of the temporal bone, it is filled with perilymph
the membranous labyrinth of the osseous is filled with?
endolymph
what are important portions of the membranous labyrinth?
vestibule, utricle, and saccule, semicircular canals and cochlea
what are the 3 semicircular canals?
- lateral
- anterior
- posterior
ampulla importance
it is a dilated portion of the canal which contains the crust ampullaris, a ridge covered in sensory hair cells
cupula importance
it is a tall, cone-shaped flap of gelatinous glycoprotein attached to the crust ampullaris, it surrounds the sterocilia and kinocilia of the hair cells
cupula and ampulla are connected how
the cupola forms a watertight seal inside the ampulla
how does endolymph affect this cupula
endolymph can deviate and bend the cupula, and thus act on the hair cells
-the cupula has a viscous drag that opposes the force of the endolymph
in the cupula, input to the system is in
angular acceleration of the head
what is the output of the hair cells in the cupula in
angular velocity
excitatory and inhibitory for:
right lateral canal and left lateral canal
-right yaw excites right lateral canal and inhibits left lateral canal
excitatory and inhibitory for:
right anterior canal and left posterior canal
-downward head pitch combined with right head roll excited right anterior canal and inhibits left posterior canal
excitatory and inhibitory for:
left anterior canal and right posterior canal
-downward head pitch combined with leftward head roll excites the left anterior canal and inhibits the right posterior canal
what is caloric stimulation
is an artificial alternative to head rotation for producing a vestibulo-ocular response. it relies on section currents in endolymph produced by warm or cold applied to one ear canal
warm air in right ear would cause
upward vection currents that stimulate a rightward head motion, which is excitatory for the right lateral canal
(with compensatory slow-phase eye movement to the left and fast saccade to the right)
cold air in the right ear would cause
downward section currents that stimulate a leftward head motion, which is inhibitory for the right lateral canal (with compensatory slow-phase eye movements to the right and fast saccade eye movement to the left)
how can COWS mnemonic help you remember caloric stimulation
Cold-Other-Warm-Same
- cold in one ear causes saccade to other side
- warm in one ear causes saccade to same side
describe the maculae of the utricle and saccule
the maculae are located roughly in perpendicular planes, both planes are actually curved
what are otoliths and how do they affect hair cells?
otoliths are calcium carbonate crystals, they are denser than endolymph and lag behind when force is applied, so they bend the hairs of the hair cells
what do the maculae transduce
the maculae transduce linear acceleration of the head and gravitational force
where are hair cell sensory receptors found?
in the crust ampullaris of the semicircular canal, the macula utriculi in the utricle, and the macula sacculi in the saccule
what does it mean when cells have a ‘tonic’ firing rate?
they are excited by force in one direction and inhibited by force in the other
hair cells only respond to forces applied along their:
plane of polarization (hair cells all have the same plane of polarization), which corresponds to the plane of the semicircular canal
what is the rotational vestibulo-ocular response (rVOR)
the response stimulated by the semicircular canal receptors, primarily non-visual
rVOR slow phase is
opposite direction to head rotation
in rVOR, slow phases are interspersed with quick phases (saccades) in
the same direction as head motion
in rVOR, the slow and quick phases comprise the
vestibulo-ocular nystagmus
when is the rotational VOR best?
best to brief head rotations
-it is not so good for responding to sustained rotation of the head
(shortest of any eye movement class)
what type of frequencies does rVOR respond best to?
high temporal frequencies
high pass system
in near vision (convergence), how is the VOR response different any why?
in near vision, the eyes must counter-rotate relatively more for the same head rotation
(gain in VOR increases during convergence of the eyes)
what is post rotatory nystagmus
it is observed when angular velocity changes after a long period of rotation at a constant angular velocity
example of post rotatory nystagmus and how
spinning in barony chair and then abrupt halt, this stilettos acceleration in the direction opposite to the original constant-velocity motion
explain the results of post-rotatory nystagmus when spinning a person clockwise at constant angular velocity just after you bring them to a halt
(and what eye movements result-slow/fast)
after halt, the head is stationary but the endolymph has inertia to continue in a clock-wise path
-this places force on cupula that simulate a counter-clockwise rotation from a standing start
(slow phase to Right, fast phase to Left)
what does it mean by vestibulo-ocular system is feed-forward?
its accuracy depends on adapting the feed-forward gain to optimize the response
the prismatic effects of spectacle lens varies in off-gaze by
prentice’s rule
prentice’s rule
p = c F
p=prismatic effect in prism diopters
c= distance from optical center in cm
F= lens power in diopters D
voluntary changes in gaze are usually accomplished by a combination of
head saccade and eye saccade
head saccade and eye saccade working together causes
head saccade produces a slow phase VOR opposite to eye saccade direction
difference between what optokinetic and VOR respond best to
optokinetic- slow, sustained optic flow
vestibulo-ocular- fast, brief head rotations
what is translational vestibulo-ocular response and is it important
they are non-visual, function is to maintain stable gaze for the whole visual environment despite linear acceleration, not too important in humans
what does the parallel swing experiment show?
used to demonstrate small pitch eye movements during linear for-aft acceleration
the arrangement of excitatory and inhibitory pathways to a single eye is an example of ‘wiring’ for :
Sherrington’s law
the arrangement of signals to yoke muscles in the two eyes is an example of wiring; for:
Hering’s law
what does the flocculus of the cerebellum do?
it is involved in VOR plasticity by integrating information and making the response more accurate
(long term visual calibration mechanism)
