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Neuroscience - Quiz 3 > 3: Control of Eye Movement > Flashcards

3: Control of Eye Movement Flashcards

1
Q

(OBJ) List and define the 7 different types of movements made by the eyes.

A
  1. Saccadic movements: small jumps; occur quickly
  2. Smooth pursuit eye movements: tracking slowly moving objects
  3. Vestibulo-ocular reflexes: produces eye movement in response to changes in head position
  4. Fixation reflex: fixate on moving target
  5. Optokinetic reflex: involuntary fixation on objects moving in relationship to head
  6. Vergence: the movement of the eye to focus close up or far away
  7. Pupillary light reflex: constriction of pupil in response to light
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2
Q

(OBJ) List the actions of the 6 extraocular muscles.

A
  1. Medial rectus: adducts eye
  2. Lateral rectus: abducts eye
  3. Superior rectus: elevate, intort, adduct eye
  4. Inferior oblique: elevate, extort, abduct eye
    - -Superior rectus + inferior oblique: elevate eye
  5. Inferior rectus: depress, extort, adduct eye
  6. Superior oblique: depress, intort, abduct eye
    - -Inferior rectus + superior oblique: depress eye
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3
Q

(OBJ) Compare and contrast saccadic eye movements and smooth pursuit.

A

Saccadic: rapid, ballistic eye movement

  • -Produced by cerebral cortex (frontal eye fields) or superior colliculus -> PPRF (horizontal) & rostral interstitial nucleus (vertical)
  • -Vision blurred during movement
  • -Head turns 20-40 msec later

Smooth pursuit: eyes move smoothly

  • -Only occurs when tracking something or in response to head movement
  • -Shares pathway with vestibulo-ocular reflex
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4
Q

Why do we need precise control of eye movement?

A

Keep visual images on equivalent location of each retina to prevent double vision

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5
Q

True/false: Most eye movements are voluntary.

A

FALSE - most eye movements are REFLEX

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6
Q

Distinguish between intorsion and extortion.

A

Intorsion: upper part of eye approaches nose

Extortion: upper part of eye approaches temporal region

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7
Q

Distinguish between convergence and divergence.

A

Convergence: bringing the pupils together

Divergence: moving the pupils away from each other

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8
Q

What is the MLF? PPRF? What results from damage to each?

A

MLF: contains ascending projections from vestibular nuclei, contributing to eye movements with changes in head position

  • -Interconnects nuclei of extraocular muscles to coordinate conjugate eye movements
  • -Damage: intenuclear opthalmoplegia (eye moving laterally not followed by medial movement of the other eye)

PPRF: critical area for voluntary conjugate horizontal eye movement
–Damage = prevent voluntary horizontal gaze towards the side of damage

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9
Q

What does the superior colliculus do? From where does it receive afferents and to where does it send efferents?

A

Site of relay of cortical control of eye movement
Afferents: retina, inferior colliculus, spinal cord, cerebral cortex
Efferents: spinal cord (tectospinal tract) and brainstem (tectoreticular tract) including PPRF and midbrain RF
Function: adjusts head and eyes toward a stimulus; saccadic movement to target

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10
Q

What is the frontal eye field? What is the occipital eye field?

A

Frontal eye field: part of the premotor cortex patterning voluntary horizontal gaze

Occipital eye field: a region near the junction of the occipital lobes with the posterior parietal and temporal lobes; includes areas of cortex involved in interpreting movement of objects -> eye movements respond to visual inputs

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11
Q

What is the pathway for voluntary horizontal gaze?

A
  1. Right frontal eye field of cortex
  2. (right superior colliculus ->) LEFT paramedian pontine reticular formation (PPRF)
  3. Left CN VI -> left lateral rectus m.
  4. -> MLF -> right CN III -> right medial rectus
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12
Q

What is the pathway for voluntary vertical gaze?

A
  1. Diffuse areas of cortex
  2. Rostral interstitial nucleus of midbrain (vertical gaze center)
  3. (-> posterior commissure) -> oculomotor & trochlear nuclei

Damage inhibits voluntary upgaze, does not affectvertical vestibuloocular reflex

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13
Q

What is the pathway for the vestibuloocular reflex?

A
  1. CN VIII
  2. Vestibular nucleus & flocculus
  3. CN VI & PPRF
  4. Through MLF to CN III, CN IV
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14
Q

What is the pathway for smooth pursuit? What two other movements use this pathway?

A

Uses some of the same wiring as the vestibuloocular reflex

  1. Awareness of a moving visual stimulus in occipital eye field (visual association areas in the occipital lobe) -> lock eyes onto target
  2. (-> frontal eye field) -> ipsilateral pontine nuclei
  3. -> middle cerebellar peduncle -> contralateral flocculus
  4. -> inferior cerebellar peduncle -> ipsilateral vestibular complex
  5. CN VI & PPRF (bilateral, some excitatory, some inhibitory)
  6. -> MLF -> CN III, IV

Also used by fixation and optokinetic reflexes

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15
Q

What is the pathway for vergence?

A

Occipital lobe -> mesencephalic reticular formation -> superior colliculus

  • -Pathway unclear
  • -Wired in parallel with acommodation
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16
Q

What is the pathway for the pupillary light reflex?

A

Afferents: optic nerves, optic chiasm, optic tract

  • -> Pretectal nucleus (processes light)
  • -> both E-W nuclei
  • -> Preganglionic parasympathetic fibers running on surface of CN III
  • -> Ciliary ganglion
  • -> Postganglionic parasympathetic fibers -> sphincter pupillae
17
Q

(OBJ) List the cranial nerves involved in regulating eye movements, including their source and what they innervate. [CN III]

A

CN III - oculomotor nerve - from interpeduncular fossa of midbrain

  • -> GSE to medial rectus, superior rectus, inferior oblique, inferior rectus, levator palpebrae superioris
  • -> GVE from E-W nucleus to ciliary ganglion -> constrictor pupillae & ciliary muscles
18
Q

Name 3 places/situations in which the oculomotor nerve can be easily damaged or compressed. What is the typical first sign of pressure on oculomotor nerve?

A

Aneurysm of posterior communicating artery or internal carotid artery
Wall of the cavernous sinus

First sign = pupillary dilation

19
Q

(OBJ) List the cranial nerves involved in regulating eye movements, including their source and what they innervate. [CN IV]

A

CN IV - trochlear nerve - decussates in brainstem, then exits from *dorsum of brainstem at ponto-mesencephalic junction

  • -> GSE to CONTRALATERAL superior oblique
  • -Long, thin - can be damaged in head trauma or lateral wall of cavernous sinus
20
Q

(OBJ) List the cranial nerves involved in regulating eye movements, including their source and what they innervate. [CN VI]

A

CN VI - abducens nerve - from abducens nucleus in floor of fourth ventricle, exits at medullary pontine junction
–> GSE to lateral rectus

21
Q

Characterize the activity of extraocular motor neurons before, during, and after eye movement.

A

Before: tonic activity
During: marked increase or decrease in firing rate
After: new resting tonic level of activity

22
Q

Why is there a 1/5 second lag before a saccade takes place?

A

To process the eye movement to assure that it is accurate

23
Q

Describe the characteristics of someone with a trochlear nerve lesion. How would a lateral rectus lesion differ?

A

Trochlear nerve (CN IV) = superior oblique

  • -Eye deviates slightly medial and extorts
  • -Head laterally flexed away from side of lesion

LR lesion = head tiles TOWARD side of abnormal eye

24
Q

What are microsaccades?

A

Minute, nearly imperceptible movements of the eye that keep an image from remaining on the same photoreceptors for too long (would -> blanching in a few seconds otherwise)

25
Q

What is jerk nystagmus? When is it seen?

A

Nystagmus with a slow and fast component

Indicates problem with vestibular system

26
Q

What is pendular nystagmus?

A

Rapidly oscillating eye movements in which oscillations are equal in both directions

27
Q

How are single eye muscles tested?

A 
The H!
Abducted -> elevation = superior rectus
Abducted -> depression = inferior rectus
Adducted -> elevation = inferior oblique
Adducted -> depression = superior oblique
Abduction = lateral rectus
Adduction = medial rectus

Neuroscience - Quiz 3 (9 decks)

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