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S2 Neuroscience > Oculomotor System > Flashcards

Oculomotor System Flashcards

1
Q

oculomotor system functions

A

controls movement of eyes

  • brings targets onto the fovea
  • keeps them there
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2
Q

what is foveation

A

the movement of both eyes in a conjugate manner to focus the fovea on a target

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3
Q

what are the 5 movement systems that have been identified to focus the fovea on a target and keep it there?

A 
vestibulo-ocular
optokinetic
saccade
smooth pursuit
vergence
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4
Q

which of the 5 movement systems…

  • stabilize the eye when the head moves
  • keep the fovea on a visual target
A 
stabilize
-vestibulo-ocular
-optokinetic
keep fovea on a visual target
-saccade
-smooth pursuit
-vergence
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5
Q

vestibulo-ocular

  • function
  • how does it do it?
  • when does it do this?
A

gaze stabilization

-vestibular input holds images stable on retina during head and body movement

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6
Q

optokinetic

  • function
  • when does it function
A

visual input holds images on retina during sustained or slow head rotation

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7
Q

saccade

-what does it do?

A

brings new objects of interest onto fovea

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8
Q

smooth pursuit

-what does it do?

A

holds image of a moving target on the fovea

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9
Q

vergence

-what does it do

A

adjusts the eyes for viewing different distances in depth

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10
Q

what is retinal disparity

A

if the oculomotor system becomes “unlocked” and the eyes focus on different targets

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11
Q

if retinal disparity occurs, what is the sign

A

diplopia (double vision)

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12
Q

all the movement systems except for vergence allow for _____ movements of the eyes for _____

A

conjugate movements of the eyes for foveation

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13
Q

vergence system allows for _____ or _____

A

convergence or divergence (disconjugate movements)

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14
Q

saccade system

-used to…

A

quickly reposition the eyes (fovea) to focus on an image that has suddenly been moved from the fovea

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15
Q

saccades can be…

A

horizontal (best understood, at least from a neuronal pathway point of view)
vertical

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16
Q

saccadic eye movements can be elicited by…

A 
visual input
other stimuli
-auditory stimuli
-memories of locations
-verbal commands
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17
Q

saccadic movement is similar to…

A

similar to the quick or saccade phase of vestibular nystagmus

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18
Q

horizontal saccade

  • this conjugate system is directed through…..
  • -location
A

directed through a horizontal gaze center
located in pontine reticular formation
-paramedial pontine reticular formation (PPRF)
adjacent to abducens nucleus

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19
Q

saccade system: UMN control

  • how is it accomplished
  • involves…
A

complicated system of interneurons
involves
-part of the middle frontal gyrus termed the Frontal Eye Fields (FEF; area 8)
-superior colliculus

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20
Q

saccade system

-cortical region that represents this system is divided into what distinct regions

A

horizontal gaze center
vertical gaze center
vergence center

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21
Q

how do the vestibulo-ocular and optokinetic reflexes work together?

A

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

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22
Q

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
A

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

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23
Q

2 components of rotatory nystagmus

A

slow movement of fixation

rapid movement of resetting

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24
Q

vestibulo-ocular reflex

-driven by _____ due to…

A

driven by vestibular system, due to directional flow of endolymph opposite the direction your head is turning

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25
Q

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

A

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)

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26
Q

optokinetic system requires input from what 2 areas?

A

visual cortex

superior colliculus

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27
Q

what happens once the rotation in a spinning chair is stopped?

  • what is this called
  • -driven by…
A

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

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28
Q

smooth pursuit

-requires…

A

image to be moving across field of vision

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29
Q

smooth pursuit

-once fixation on the image has been established, movements are not…

A

under volitional control

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30
Q

smooth pursuit

-“UMN” control comes from…

A

visual signals from primary visual cortex, channeled through an area in the caudal temporal gyrus, coupled with superior colliculus

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31
Q

PPRF function in controlling saccade and smooth pursuit conjugate eye movements
-how are these neurons activated…

A

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

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32
Q

all systems for conjugate eye movements influenced by _____ via…
-examples

A

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

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33
Q

vergence system

-controlled through _____ at _____

A

reticular formation at the midbrain level

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34
Q

why are disconjugate movements of the eye necessary?

A

necessary for foveation of an image as it moves toward or away from you

35
Q

for convergence, what must happen with the muscles

A

activation of both medial rectus muscles must override the lateral rectus muscle tone to bring the eyes together

36
Q

during convergence, to overcome blurring of the image as it comes closer, what mechanism is it coupled with?

A

coupled with pupillary constriction and accommodation (rounding of the lens) for changing of focal distances

37
Q

location of cortical control of the

  • vergence system
  • pupillary constriction and accommodation
A

visual cortical areas
vergence gaze center
-area rostral to the horizontal gaze center

38
Q

anatomical structures involved in the oculomotor system

A

superior colliculus

pretectal area

39
Q

superior colliculus

-location of nucleus

A

rostral in the midbrain tectum (region dorsal to the cerebral aqueduct of Sylvius)

40
Q

superior colliculus

-receives UMN fibers from…

A

ipsilateral cortex (frontal eye fields (area 8), occipital lobe, caudal temporal lobe

41
Q

explain relationship between tectobulbar connections to the nuclei of the cranial nerves innervating the extraocular eye muscles

A

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)

42
Q

superior colliculus receives direct retinal projections from _____ via _____

A

projections from optic tract via the brachium of the superior colliculus

43
Q

superior colliculus

-descending efferent information is directed to…

A

spinal cord

cranial nerve nuclei

44
Q

superior colliculus: tectospinal tract

  • crosses in…
  • descends to…
  • function
A

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

45
Q

pretectal area

  • composed of…
  • located…
A

composed of a number of nuclei

located rostral to the superior colliculus

46
Q

pretectal area

-receives projections from…

A

cortex, retina, and superior colliculus

47
Q

pretectal area

  • efferents directed to…
  • -what is the information’s purpose when it reaches its destination
A

cranial nerve motor nuclei and preganglionic parasympathetic neurons associated with CN III for reflex control and pupil lens

48
Q

how are all CNs involved with movement of the eye interconnected?

A

through axons traveling in the medial longitudinal fasciculus (MLF)

49
Q

CN VI LMNs

  • innervate…
  • exit where?
A

lateral rectus

exit brainstem laterally, adjacent to the pyramids at the pontomedullary junction

50
Q

CN VI

-function

A

abduction of the eyeball

51
Q

_____ fibers terminate in a _____ nucleus adjacent to the abducens nucleus
-what is the name of this nucleus where they terminate?

A

tectobulbar fibers
reticular formation nucleus
paramedian pontine reticular formation (PPRF; horizontal gaze center)

52
Q

PPRF projects to…

A

abducens nucleus

53
Q

horizontal conjugate gaze

-internuclear neurons from the abducens nucleus project to the _____ for _____

A

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

54
Q

horizontal conjugate gaze

  • internuclear neurons from PPRF project to the _____ for _____
  • these axons run in…
A

project to the contralateral oculomotor complex for activation of contralateral medial rectus
these axons run in the contralateral MLF

55
Q

strabismus

  • what is it
  • also called…
A

visible turn of one eye that may be constant

also termed tropia (esotropia or exotropia)

56
Q

phoria

-refers to…

A

refers to the point of vergence of the eyes

57
Q

esophoria

-what is it

A

eyes are postured in front of the point of focus

58
Q

exophoria

-what is it

A

eyes are postured in back of the point of focus

59
Q

how are eso/exophoria different from myo/hyperopia

A

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

60
Q

esotropia

  • what is it?
  • caused by…
A

unopposed adduction of the eye

caused by lesion of the ipsilateral abducens nerve

61
Q

lesion of the abducens nucleus (includes PPRF) results in paralysis of _____ on what side relative to the lesion

A

paralysis of horizontal gaze ipsilateral to the lesion

62
Q

internuclear ophthalmoplegia

  • occurs due to…
  • results in…
A

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)

63
Q

in internuclear ophthalmoplegia

  • abducting eye will exhibit…
  • -due to…
A

will exhibit pendular nystagmus

thought to be due to loss of inhibitory fibers in MLF

64
Q

CN IV

-LMNs innervate…

A

contralateral superior oblique muscle

65
Q

CN IV

-LMN axons location

A

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

66
Q

CN IV functions

A

rotation and depression of eyeball

67
Q

CN IV lesion (rare)

-results in…

A

inability to look down

-problems walking down stairs

68
Q

CN IV lesion

-vertical gaze is coordinated through…

A

vertical gaze center (interstitial nucleus of Cajal; located near trochlear nucleus)

69
Q

CN III

-LMNs innervate

A

remainder of extraocular eye muscles
levator palpebrae superioris
all ipsilateral, except to superior rectus

70
Q

CN III

-contains _____ fibers to _____

A

contains preganglionic parasympathetic fibers to the ciliary ganglia

71
Q

CN III: preganglionic parasympathetic cell bodies

-location

A

in an adjacent nucleus

-Edinger-Westphal nucleus

72
Q

CN III: how do all fibers (LMN’s and preganglionic) exit?

-where can this nerve be seen exiting?

A

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

73
Q

exotropia

  • what is it?
  • due to…
A

unopposed abduction of the ipsilateral eye
due to
-lesion of oculomotor nerve

74
Q

lesion of CN III

  • results in…
  • causes paralysis of…
A

oculomotor palsy

causes paralysis of all extraocular eye muscles except lateral rectus and superior oblique

75
Q

apart from eye movement problems, what else is noted with oculomotor palsy

A

drooping of eyelid due to involvement of levator palpebrae superioris

76
Q

CN III

-dilation (mydriasis) of the pupil due to loss of…

A

parasympathetic innervation of the ciliary ganglia

77
Q

Argyll-Robertson pupil

  • seen in…
  • characteristics…
A

seen in tertiary syphilis
pupil is small in dim light and non-reactive to light
will constrict in accommodation associated with convergence

78
Q

alternating hemiplegias

  • possible causes
  • -what type of alternating hemiplegias are involved with each
A

Abducens or middle alternating hemiplegia

oculomotor or superior alternating hemiplegia

79
Q

Horner’s Syndrome

  • lesion of…
  • -what was the function of these structures?
A

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

80
Q

Horner’s Syndrome

-if involvement is to sympathetics directed to the head, which structures are involved?

A

ascending sympathetic chain

superior cervical ganglion

81
Q

Horner’s Syndrome

-clinical manifestation if sympathetics direct to the head are injured

A
  • ptosis (drooping eyelid)
  • miosis (pupil constricted)
  • dry skin (absence of seating)
  • flushed skin (lack of constriction of capillary field
82
Q

Horner’s Syndrome

-why does ptosis occur?

A

due to loss of sympathetic innervation to superior tarsal muscle of the eyelid and its control by levator palpebrae superioris

83
Q

Horner’s Syndrome

-why does miosis occur?

A

loss of dilator control

-unopposed constrictor tone (parasympathetic)

S2 Neuroscience (25 decks)

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