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Neuro Exam 3 > Control of Eye Movements > Flashcards

Control of Eye Movements Flashcards

1
Q

What do normal eye movements require?

A

Head movements = vestibular info

Visual objects = vision

Eye movement and position = proprioceptive info (LMN)

Selection of visual target = brainstem and cortical areas

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2
Q

What do you need to control eye position?

A

Medial longitudinal fasiculus

Reflexes

Cerebral centers

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3
Q

Describe saccadic.

A

Rapid eye movements that bring image of object onto fovea

Jumpy

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4
Q

Describe Smooth Pursuit.

A

Keeps moving image centered on fovea.

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5
Q

Describe Vestibular-ocular. Control systems?

A

Holds image steady on fovea during head movement.

Control systems:
Semicircular canals
Vestibular nuclei

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6
Q

Describe Vergence. Control systems?

A

Keeps image on fovea when object is moved near

Control systems:
Unknown direct input to oculomotor neurons, likely through interneurons

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7
Q

Name the conjugate movements.

A

Saccadic

Smooth pursuit

Vestibular-ocular

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8
Q

Name the disconjugate movements.

A

Vergence

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9
Q

Describe Optokinetic movement. What happens at the end?

A

Smooth pursuit + head movement
Smooth pursuit + nuclei of accessory optic system

Hold image of target steady on retina during sustained head rotation

Requires intact parietooccipital eye field

At the end:
Visual target is broken when target reaches limit of visual field
Eyes make quick move in the opposite direction = optokinetic nystagmus

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10
Q

Describe Nystagmus quick phase. Control mechanism?

A

Directs fovea toward oncoming visual scene during self-rotation; resets eyes during prolonged rotation.

Control mechanism:
Cortical

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11
Q

What are the control mechanisms of horizontal saccadic system?

A

Frontal eye fields - voluntary saccades

Superior colliculus - reflexes

Pontine paramedial RF (PPRF) - horizontal gaze center

CN 6 + CN 3

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12
Q

What are the control mechanisms of vertical saccadic system?

A

Frontal eye fields

Superior colliculus

Rostral Interstitial Nucleus of Medial Longitudinal Fasiculus (riMLF) - vertical gaze center

CN 4 + CN 3

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13
Q

Where is the riMLF found?

A

Near the superior colliculus and posterior commissure

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14
Q

What does a tumor of the pineal gland compress?

A

Superior midbrain leading to selective palsies of vertical gaze

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15
Q

What does a lesion near the red nucleus lead to?

A

Selective palsies where you cannot look down

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16
Q

How does horizontal saccadic eye movement occur? What is the ultimate effect?

A

Input sent to the contralateral abducens nuclei at the PPRF. (Input = frontal eye fields)

There abducens nerve fibers will run to the contralateral lateral rectus muscle.

Or send nerve fibers to the ipsilateral oculomotor nucleus using the medial longitudinal fasciculus.

Never fibers synapse there and CN 3 nerve fibers leave to innervate the ipsilateral medial rectus muscle.

Ultimate effect = rapid conjugate deviation toward OPPOSITE SIDE

(ipsilateral and contralateral in relation side “activated” - so right frontal field activation will lead to activation of the right medial rectus and the left lateral rectus are activated. Right frontal field = left movement of eye)

17
Q

What contributes to reflexive saccadic eye movements?

A

Supplementary and Parietal eye fields

Superior colliculus

18
Q

What needs to happen for a saccadic movement to occur?

A

1) BURST of neuronal firing = excitatory burst neurons
To move eyes toward target

2) TONIC neuronal firing = tonic neurons
For locking and fixing on target

3) PAUSE neurons = inhibit burst neurons once target is fixed so no further movement occurs

19
Q

Control centers for saccadic movement is different for horizontal and vertical movements. What are the control centers for HORIZONTAL MOVEMENT?

A

Burst cells = PPRF

Tonic cells = Nucleus prepositus hypoglossi

Pause cells = Omnipause cells of Raphe nuclei

20
Q

What are the control centers for VERTICAL MOVEMENT?

A

Burst cells = Rostral interstitial nucleus of MLF

Tonic cells = Interstitial nucleus of Cajal

Pause cells = Omnipause cells of Raphe nuclei

21
Q

Where on the brainstem are vertical and horizontal gaze center found?

A

Vertical = midbrain region

Horizontal = PONS, upper medulla

22
Q

What happens if you have a destructive lesion at the frontal gaze center?

A

Eye deviates TOWARD side of lesion

Difficulty looking away from lesion

23
Q

What happens if you have seizure activity at the frontal gaze center?

A

Eyes deviates AWAY from firing gaze center

24
Q

What are the control mechanisms for smooth pursuit?

A

Parietooccipital cortex (Brodmann’s area 19)

Vestibulocerebellum

Pons

Medial vestibular nuclei (horizontal - CN 6+3, vertical - CN 4+3)

25
Q

Describe the pathway through which smooth pursuit occurs. What is the ultimate effect?

A

Ultimate effect = conjugate deviation TOWARD direction of movement of object – ipsilateral to Parietooccipital cortex

Suppose the RIGHT Parietooccipital cortex is activated.

It will send fibers to the RIGHT pontine nuclei –> LEFT vestibulocerebellum –> LEFT Vestibular nuclei

The contralateral vestibular nuclei will send fibers to the ipsilateral (RIGHT) Abducens nuclei.

CN 6 fibers will then go to the ipsilateral (RIGHT) lateral rectus.

Other fibers from the Abducens nuclei –> contralateral (LEFT) oculomotor nuclei –> LEFT medial rectus

Right activation = right movement of eyes

26
Q

What are the control systems of the Optokinetic eye movements?

A

Visual pathway and parietooccipital cortex
Vestibulocerebellum
Vestibular nuclei

27
Q

What would you ask a patient to do to test saccadic movement?

A

Ask them to jump from one object to the next.

28
Q

What would you ask a patient to do to test smooth pursuit?

A

Have them visually track a slow moving object

Look at an Optokinetic tape

29
Q

If a patient had a lesion at the parietal lobe, what would be affected in regards to eye movement?

A

There will be a loss of smooth pursuit movement toward side of lesion.

No optokinetic nystagmus when tape is moved toward damaged lobe.

30
Q

Describe the pathway through which vestibular-ocular system occurs. What is the ultimate effect?

A

Ultimate effect = movement of eye OPPOSITE to head rotation

So suppose the head turns to the RIGHT: it activates the RIGHT labyrinth

CN 8 will travel from RIGHT labyrinth –> RIGHT vestibular nuclei –> Fibers to contralateral (LEFT) abducens nuclei –>

Abducens nuclei –> contralateral (LEFT) lateral rectus

Abducens nuclei –> MLF –> ipsilateral (RIGHT) oculomotor nucleus –> ipsilateral (RIGHT) medial rectus

31
Q

What is internuclear ophthalmoplegia (INO)? What causes it?

A

Impaired horizontal eye movements

Weak adduction of affected eye
Abduction nystagmus of contralateral eye

Cause = lesion in MLF

32
Q

What needs to happen for the near reflex to occur?

A

Convergence = image on the fovea

Accommodation = lens thickens to image focused on fovea

Pupillary constriction = better optical performance

33
Q

Describe the pathway for the near reflex or vergence?

A

First - normal visual pathway synapsing at LGN and then primary visual cortex

Then - PVC sends fibers to Visual association cortex

Visual association cortex –> superior colliculus or pretectal plate or both –> Oculomotor n. and Edinger-westphal nucleus

Oculomotor n. to make the eyes converge and EWN for pupillary constriction

34
Q

How would you test a patient’s vestibular-ocular movements?

A

Doll’s eye maneuver = eyes move in opposite direction of head turning

Ice water caloric = COWS

35
Q

When would you see a deficiency in vestibular-ocular movements?

A

In a comatose patient with dysfunction at the level of the brainstem

Doll’s yes and Ice water caloric will be absent

36
Q

How would you test vergence?

A

Have patient focus on near object and see if near reflex occurs

37
Q

What is Argyll-Robertson pupil?

A

Occurs from neurosyphilis

Absent light reflex but pupil constricts in near reflex testing

Neuro Exam 3 (8 decks)

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