Oculomotor System Flashcards
oculomotor system functions
controls movement of eyes
- brings targets onto the fovea
- keeps them there
what is foveation
the movement of both eyes in a conjugate manner to focus the fovea on a target
what are the 5 movement systems that have been identified to focus the fovea on a target and keep it there?
vestibulo-ocular optokinetic saccade smooth pursuit vergence
which of the 5 movement systems…
- stabilize the eye when the head moves
- keep the fovea on a visual target
stabilize -vestibulo-ocular -optokinetic keep fovea on a visual target -saccade -smooth pursuit -vergence
vestibulo-ocular
- function
- how does it do it?
- when does it do this?
gaze stabilization
-vestibular input holds images stable on retina during head and body movement
optokinetic
- function
- when does it function
visual input holds images on retina during sustained or slow head rotation
saccade
-what does it do?
brings new objects of interest onto fovea
smooth pursuit
-what does it do?
holds image of a moving target on the fovea
vergence
-what does it do
adjusts the eyes for viewing different distances in depth
what is retinal disparity
if the oculomotor system becomes “unlocked” and the eyes focus on different targets
if retinal disparity occurs, what is the sign
diplopia (double vision)
all the movement systems except for vergence allow for _____ movements of the eyes for _____
conjugate movements of the eyes for foveation
vergence system allows for _____ or _____
convergence or divergence (disconjugate movements)
saccade system
-used to…
quickly reposition the eyes (fovea) to focus on an image that has suddenly been moved from the fovea
saccades can be…
horizontal (best understood, at least from a neuronal pathway point of view)
vertical
saccadic eye movements can be elicited by…
visual input other stimuli -auditory stimuli -memories of locations -verbal commands
saccadic movement is similar to…
similar to the quick or saccade phase of vestibular nystagmus
horizontal saccade
- this conjugate system is directed through…..
- -location
directed through a horizontal gaze center
located in pontine reticular formation
-paramedial pontine reticular formation (PPRF)
adjacent to abducens nucleus
saccade system: UMN control
- how is it accomplished
- involves…
complicated system of interneurons
involves
-part of the middle frontal gyrus termed the Frontal Eye Fields (FEF; area 8)
-superior colliculus
saccade system
-cortical region that represents this system is divided into what distinct regions
horizontal gaze center
vertical gaze center
vergence center
how do the vestibulo-ocular and optokinetic reflexes work together?
as your head turns, your eyes are fixed on an object
eyes remain fixed and focused on that position by moving at the same speed as your head, but in the opposite direction
-driven by bilateral input of the vestibular system
when the eyes reach a point in the periphery where they can no longer focus on an object due to the image being directed to the peripheral retina, what happens?
- what would we term this movement to be?
- effect on the visual system
- what is this while occurrence called
reset to a new fixation point
this rapid movement is a saccade
rapid enough that visual input is momentarily impaired until the foveas fixate on the next point
termed a rotatory nystagmus
2 components of rotatory nystagmus
slow movement of fixation
rapid movement of resetting
vestibulo-ocular reflex
-driven by _____ due to…
driven by vestibular system, due to directional flow of endolymph opposite the direction your head is turning
if you continue to rotate your head, such as in a spinning chair, what happens within the vestibular system and what is the result?
-what system is not driving this movement
endolymph catches up/stabilizes
same pattern of following and saccadic reset reaction continues to take place as long as your head continues to turn
-driven by optokinetic system (since the vestibular input is balanced)
optokinetic system requires input from what 2 areas?
visual cortex
superior colliculus
what happens once the rotation in a spinning chair is stopped?
- what is this called
- -driven by…
eyes will react in the opposite direction
slow following eye movement will be in the direction of prior rotation and the saccade in the opposite direction of prior rotation
knows as postrotatory nystagmus
-driven by vestibular system
smooth pursuit
-requires…
image to be moving across field of vision
smooth pursuit
-once fixation on the image has been established, movements are not…
under volitional control
smooth pursuit
-“UMN” control comes from…
visual signals from primary visual cortex, channeled through an area in the caudal temporal gyrus, coupled with superior colliculus
PPRF function in controlling saccade and smooth pursuit conjugate eye movements
-how are these neurons activated…
reflexive pathways such as the vestibulo-ocular reflex (quick phase of nystagmus)
voluntarily as in the saccades initiated from the appropriate center of Frontal Eye Fields
all systems for conjugate eye movements influenced by _____ via…
-examples
cerebellum via feedback information to the vestibular nuclei and then to the horizontal and/or vertical gaze centers
examples
-flocculus responds to difference in head versus eye movements and “adjusts” the interneurons of the vestibular nuclei to correct the velocity of the eye movements to match the head movements
vergence system
-controlled through _____ at _____
reticular formation at the midbrain level
why are disconjugate movements of the eye necessary?
necessary for foveation of an image as it moves toward or away from you
for convergence, what must happen with the muscles
activation of both medial rectus muscles must override the lateral rectus muscle tone to bring the eyes together
during convergence, to overcome blurring of the image as it comes closer, what mechanism is it coupled with?
coupled with pupillary constriction and accommodation (rounding of the lens) for changing of focal distances
location of cortical control of the
- vergence system
- pupillary constriction and accommodation
visual cortical areas
vergence gaze center
-area rostral to the horizontal gaze center
anatomical structures involved in the oculomotor system
superior colliculus
pretectal area
superior colliculus
-location of nucleus
rostral in the midbrain tectum (region dorsal to the cerebral aqueduct of Sylvius)
superior colliculus
-receives UMN fibers from…
ipsilateral cortex (frontal eye fields (area 8), occipital lobe, caudal temporal lobe
explain relationship between tectobulbar connections to the nuclei of the cranial nerves innervating the extraocular eye muscles
tectobular connections are part of the pathway for voluntary and involuntary movements of the eyes, and are analgous to “UMNs” (area 8 projects to superior colliculus)
superior colliculus receives direct retinal projections from _____ via _____
projections from optic tract via the brachium of the superior colliculus
superior colliculus
-descending efferent information is directed to…
spinal cord
cranial nerve nuclei
superior colliculus: tectospinal tract
- crosses in…
- descends to…
- function
crosses in midbrain
descends to cervical spinal cord levels
important in the reflex turning of the head and neck in response to both visual and auditory cues
pretectal area
- composed of…
- located…
composed of a number of nuclei
located rostral to the superior colliculus
pretectal area
-receives projections from…
cortex, retina, and superior colliculus
pretectal area
- efferents directed to…
- -what is the information’s purpose when it reaches its destination
cranial nerve motor nuclei and preganglionic parasympathetic neurons associated with CN III for reflex control and pupil lens
how are all CNs involved with movement of the eye interconnected?
through axons traveling in the medial longitudinal fasciculus (MLF)
CN VI LMNs
- innervate…
- exit where?
lateral rectus
exit brainstem laterally, adjacent to the pyramids at the pontomedullary junction
CN VI
-function
abduction of the eyeball
_____ fibers terminate in a _____ nucleus adjacent to the abducens nucleus
-what is the name of this nucleus where they terminate?
tectobulbar fibers
reticular formation nucleus
paramedian pontine reticular formation (PPRF; horizontal gaze center)
PPRF projects to…
abducens nucleus
horizontal conjugate gaze
-internuclear neurons from the abducens nucleus project to the _____ for _____
internuclear neurons from the abducens nucleus (different than interneurons of PPRF) project to the ipsilateral oculomotor complex for inhibition of ipsilateral LMNs innervating medial rectus
horizontal conjugate gaze
- internuclear neurons from PPRF project to the _____ for _____
- these axons run in…
project to the contralateral oculomotor complex for activation of contralateral medial rectus
these axons run in the contralateral MLF
strabismus
- what is it
- also called…
visible turn of one eye that may be constant
also termed tropia (esotropia or exotropia)
phoria
-refers to…
refers to the point of vergence of the eyes
esophoria
-what is it
eyes are postured in front of the point of focus
exophoria
-what is it
eyes are postured in back of the point of focus
how are eso/exophoria different from myo/hyperopia
myo/hyperopia refer to where the image is focused with respect to the retina
eso/exophoria refer to where the point of vergence is with respect to the object the patient is viewing
esotropia
- what is it?
- caused by…
unopposed adduction of the eye
caused by lesion of the ipsilateral abducens nerve
lesion of the abducens nucleus (includes PPRF) results in paralysis of _____ on what side relative to the lesion
paralysis of horizontal gaze ipsilateral to the lesion
internuclear ophthalmoplegia
- occurs due to…
- results in…
MLF damaged in pons
actions of the abducens and oculomotor nerves are uncoupled
-excursion of the abducting eye is full, but adduction of the other eye is impaired (this is the side of the damage)
in internuclear ophthalmoplegia
- abducting eye will exhibit…
- -due to…
will exhibit pendular nystagmus
thought to be due to loss of inhibitory fibers in MLF
CN IV
-LMNs innervate…
contralateral superior oblique muscle
CN IV
-LMN axons location
course dorsally around the periaqueductal grey and decussate
nerve then courses around the brainstem to occupy a position lateral to the oculomotor nerve bewteen the superior cerebellar and posterior cerebral arteries
CN IV functions
rotation and depression of eyeball
CN IV lesion (rare)
-results in…
inability to look down
-problems walking down stairs
CN IV lesion
-vertical gaze is coordinated through…
vertical gaze center (interstitial nucleus of Cajal; located near trochlear nucleus)
CN III
-LMNs innervate
remainder of extraocular eye muscles
levator palpebrae superioris
all ipsilateral, except to superior rectus
CN III
-contains _____ fibers to _____
contains preganglionic parasympathetic fibers to the ciliary ganglia
CN III: preganglionic parasympathetic cell bodies
-location
in an adjacent nucleus
-Edinger-Westphal nucleus
CN III: how do all fibers (LMN’s and preganglionic) exit?
-where can this nerve be seen exiting?
traverse the tegmentum near the red nucleus and cross the cerebral peduncles to exit in the interpeduncular fossa
can be seen exiting between the superior cerebellar and posterior cerebral arteries
exotropia
- what is it?
- due to…
unopposed abduction of the ipsilateral eye
due to
-lesion of oculomotor nerve
lesion of CN III
- results in…
- causes paralysis of…
oculomotor palsy
causes paralysis of all extraocular eye muscles except lateral rectus and superior oblique
apart from eye movement problems, what else is noted with oculomotor palsy
drooping of eyelid due to involvement of levator palpebrae superioris
CN III
-dilation (mydriasis) of the pupil due to loss of…
parasympathetic innervation of the ciliary ganglia
Argyll-Robertson pupil
- seen in…
- characteristics…
seen in tertiary syphilis
pupil is small in dim light and non-reactive to light
will constrict in accommodation associated with convergence
alternating hemiplegias
- possible causes
- -what type of alternating hemiplegias are involved with each
Abducens or middle alternating hemiplegia
oculomotor or superior alternating hemiplegia
Horner’s Syndrome
- lesion of…
- -what was the function of these structures?
lesion of sympathetic nervous system pathway
descending influence from the hypothalamus directed to preganglionic sympathetic neurons in the spinal cord, or any of the peripheral pathways carrying sympathetic fibers
Horner’s Syndrome
-if involvement is to sympathetics directed to the head, which structures are involved?
ascending sympathetic chain
superior cervical ganglion
Horner’s Syndrome
-clinical manifestation if sympathetics direct to the head are injured
- ptosis (drooping eyelid)
- miosis (pupil constricted)
- dry skin (absence of seating)
- flushed skin (lack of constriction of capillary field
Horner’s Syndrome
-why does ptosis occur?
due to loss of sympathetic innervation to superior tarsal muscle of the eyelid and its control by levator palpebrae superioris
Horner’s Syndrome
-why does miosis occur?
loss of dilator control
-unopposed constrictor tone (parasympathetic)
