17 - Eye Movements and Sensory Integration Flashcards
What is the VOR?
What is the function of it?
When do human use VOR? +how?
-when HEAD rotates eyes move in opposite direction
-keeps visual word stable
-when we walk ->VOR counter-rotates eyes to keep visual image from moving
Why is the VOR important?
keep visual world stable. if eyes move relative to the world -> image moves across retina and creates blurring (not good for survival)
What is OKR?
How does it work? give example?
-optokinetic reflex =response to movement of the whole retinal image
-the eyes follow the surround movement so that the image stays stable on the retina
What are the two stabilising eye reflexes?
VOR OKR
Why do we make saccades?
to fixate item of interest on fovea
What is smooth pursuit ?
following slow-moving targets by keeping them on the fovea
What is vergence?
function?
vergence uses smooth pursuit or saccades?
–eyes move in opposite direction to track objects moving towards/further away
-both
What are the eye movements which acquire and follow targets?
saccades, smooth pursuit, vergence
Which system senses the head rotating?
vestibular
Which eye reflex is affected by damage to the vestibular system?
VOR
Where do primary vestibular afferents project to and from?
Where are their soma located?
Thus where do primary vestibular afferents synapse?
-from semicircular canal to medial vesitbular nucleus
-with cell bodies in Scarpa’s ganglion (outside brain)
-medial vestibular nucleus
Where do neurons from the medial vestibular nucleus project to?
-synapse at abducens nucleus
What are the two man eye muscles?
medial rectus and lateral rectus
What are the two pathways projecting from the adducens nucleus?
-oculomotor neurons projecting DIRECT to lateral rectus muscle
OR oculomotor neurons project to oculomotor nucleus + another oculomotor neuron to medial rectus muscle (INDIRECT)
What is a the general reflex arc for VOR?
primary vestibular afferents sense head rotation and synapse with interneurons in vestibular nuclei -> interneurons synapse with oculomotor nuclei which cause ocular muscle contraction
What is output and input of VOR arc?
What sort of control is this an example of and why?
input head rotation
output eye movement
-feedforward control because output does not affect input at all
How is the OKR reflex arc similar to the VOR “?
How does the OKR differ from VOR?
-OKR arc projects to vestibular system nuclei and oculomotor nuclei
-however OKR input comes from retina or pretectum (retinal slip) and OKR output is eye movement
What is the retinal slip?
the whole retinal image
Is the OKR a feedforward reflex arc? why
no VOR - feedforward
OKR - feedback as output affects input
Why do we need both OKR and VOR?
What is relationship between VOR and OKR?
-we need VOR as OKR does not work well with rapidly changing movements of eg head
thus we also need OKR because VOR does not work well for low frequency constant movements (semicircular canals stop responding to constant head movement)
-yes VOR and OKR work together
What does the VOR use to know how big of a command to send eye muscle? how much should ocular muscle move?
What is an example of this experimentally?
subconscious learning of a motor skill
-monkey with minifying glasses move eyes too far in relation to head movement but after some training
the gain of VOR is reset
Why do we need both VOR and OKR?
-The OKR works well for low-frequency movements, but poorly for high-frequency movements because of feedback delays in the retina
The VOR works well for high-frequency movements, but poorly for very low frequency movements because of the mechanics of the semi-circular canals
How does the cerebellum contribute to control of VOR?
VOR is calibrated by cerebellum using the retinal slip as an error signal -> accurate reflex
Why do patients with damage to spinocerebellum have difficulty controlling walking movements?
calibration of the VOR is impaired as cerebellum is damaged
