Eye Movements Flashcards
extorsion v intorsion
extorsion- upper portion of eye approaches temporal region
intorsion- upper portion of eye approaches nose
every movement above or below the horizontal plane involves at least 2 muscles
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muscles involved in up and down gaze
upgaze:
superior rectus
inferior oblique
downgaze:
inferior rectus
superior oblique
superior rectus actions
elevate, intort, adduct
inferior oblique actions
elevate, extort, abduct
inferior rectus actions
depress, extort, adduct
superior oblique actions
depress, intort, abduct
how do you test the individual eye muscles
lateral and medial rectus- just have eyes move horizontally
during adduction- vertical movement tests inferior and superior oblique
during abduction- vertical movement tests inferior and superior rectus
where do the cranial nerves controlling eye movements emerge from the brain
CN3- interpenduncular fossa
CN4- dorsum of brainstem
CN6- medullary/pontine junction
which CN crosses the midline and innervates contralaterally
trochlear innervates contralateral superior oblique
CN3
somatic efferent innervation of medial, inferior, superior rectus, and inferior oblique
somatic innervation of levator palpebrae superioris
parasympathetics for accomodation
edinger-westphal nucleus
parasympathetic nucleus in brainstem that is the preganglionic portion of the chain for accomodation
compression of CN3 results in what first?
pupillary dilation- parasympathetics are on the outside of the nerve, and when it gets compressed, those fibers are lost first
how do CN3, 4, 5, and 6 traverse the cavernous sinus
3, 4, 5 thru the lateral wall
6 thru the center
extraocular motor neuron activity
contain a tonic activity. abduction increases firing rate and adduction decreases firing rate. at the new position, there is a new resting tonic level of activity
saccade
rapid, voluntary eye movement
vision completely blurs during movement
generated by the frontal eye fields and superior colliculus
microsaccades
keep the image from remaining on the same conors or rods for too long
conjugate horizontal gaze
saccadic
example: looking left
right frontal eye field- go to right superior colliculus and left paramedian pontine reticular formation (PPRF). right superior colliculus projects to left PPRF. PPRF projects to left CN6 then thru the MLF to right CN3
superior colliculus inputs
has inputs from retina for vision, inferior colliculus for sound, spinal cord for somatic sensations, and cerebral cortex
motor inputs are deep, visual inputs are superficial
stimulation triggers eye and head movement towards stimuli of interest
MLF
contains fibers from abducens to oculomotor to yoke these two nuclei together during horizontal gaze
also contains projections from vestibular nuclei, allowing eye movement to correspond with head movement
vertical gaze pathways
no distinct cortical center - projects to rostral interstitial nucleus (rostral midbrain)- projects bilaterally to oculomotor and trochlear nuclei
rostral midbrain projects thru posterior commissure, specifically for upgaze
vestibulo-ocular reflex
CN8- projects to vestibular nucleus and flocculus
flocculs projects to vestibular nucleus
vestibular nucleus projects to abducens and PPRF
these are connected to CN3 and 4 via MLF
smooth pursuit
move smoothly when tracking something
similar to vestibulo occular reflex
pathway: occipital eye field to ipsilateral pontine nuclei (and indirectly thru frontal eye field).
ipsilateral pontine nuclei thru middle cerebellar peduncle to contralateral flocculus
contralateral flocculus thru inferior cerebellar peduncle to ipsilateral vestibular complex
vestibular complex to CN6 and PPRF
PPRF and Cn6 thru MLF to CN3 , 4
fixation reflex
ability to fixate on a moving target
smooth pursuit pathways used
