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Neuroanatomy 2 > Eye movements > Flashcards

Eye movements Flashcards

1
Q

Where do most of the optic tract fibers go?

A

To the LG nucleus in the thalamus,

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2
Q

Other than the LG nucleus, where else do the optic tract fibers go?

A

Superior colliculus, very automatic and short - a reflex!

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3
Q

What does the dorsal stream do? and where does it end?

A

Identifies where the object is in space and ends in the parietal cortex

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4
Q

What does the ventral stream do?and where does it end?

A

The “what pathway” - to temporal cortex for object identification

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5
Q

what are the two vertical gaze centers? midbrain!

A

rostral interstitial nucleus of the MLF (riMLF)

The interstitial nculeus of cajal (INC) (Neural integrator)

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6
Q

what does the superior colliculus do?

A

Reflex saccades

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7
Q

What two structures relating to visual fields does the pons hold?

A
  1. 6th nerve nucleus

2. Horizontal gaze center - PPRF (paramedian pontine reticular formation)

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8
Q

What does the border between the pons and medulla include?

A
  1. Vestibular nuclei

2. Nucleus prepositus hypoglossi - (neural integrator)

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9
Q

What does the NPH do?

A

Holds the eye on a target

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10
Q

What does the PPRF do?

A

tells the 6th nerve nucleus what to do!

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11
Q

What 3 things are present in the midbrain which relate to eye movement?

A
  1. 3rd CN
  2. riMLF
  3. 4th CN
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12
Q

What is the function of the VOR?

A

To keep the eyes still in space by rotating eyes in opposite direction to the head

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13
Q

What 4 things happen when you rotate the head to the right?

A
  1. activate the right vestibular nucleus
  2. Activate 6th nerve nucleus
  3. contraction of the left LR
  4. activation of right CN3 and right MR
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14
Q

What is the phasic response in the VOR?

A
  1. Occurs in the vestibular afferents
  2. senses how fast you rotate
    - PULSE - higher frequency
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15
Q

To maintain eyes fixated on the left with a right head rotation what needs to happen?

A
  1. “step” phase - lower frequency
  2. Indirect pathway through NPH (nucleus prepositus hypoglossi)
    (constant firing of neurons)
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16
Q

What does the NPH do?

A

Converts the pulse or phasic activity into a tonic activity

responsible for horizontal movements

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17
Q

What is the Pulse or phasic activity from the canal proportional to?

A

Eye velocity

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18
Q

What is the tonic activity proportional to?

A

Eye position

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19
Q

Which nucleus in the midbrain acts as the integrator for vertical movements?

A

Interstitial nucleus of cajal

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20
Q

After how long does the VOR fade/habituate?

A

30 seconds

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21
Q

How does the visual system compensate for the fading VOR?

A

The optokinetic reflex

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22
Q

What is the OKR?

A

Combination of slow pursuit and saccade eye movements -
slow movement in direction of stimulus followed by fast, corrected saccades
- needed when there is sustained slow movement - or large object moving across visual field

23
Q

How fast are saccades?

A

900 degrees per second - can change direction/position but not this velocity!!!

24
Q

How are saccades generated?

A
  1. Phasic burst of AP originating in the PPRF
25
Q

What does the right PPRF do?

A

generates conjugate ipsilateral rotations

26
Q

How does the SHORT pathway via the SUPERIOR COLLICULUS respond to flashing/moving stimulus in peripheral retina?

A

Contralateral INVOLUNTARY reflex saccade via the PPRF in the pons

27
Q

What stimuli does the SC receive?

A
  1. Auditory - loud sound
  2. Somatosensory - spinal cord - tap on shoulder
  3. flashing/moving stimulus
28
Q

What gives the command when we want to make a voluntary saccade?

A

Parietal eye field - where

Frontal eye field - make the move

29
Q

Describe the path from the left FEF….to generate a SACCADE - (think PPRF) (move eye to right)

A
  1. project to left SC
  2. cross to contralateral PPRF
  3. to right abducens (abduct right eye)
  4. to LEFT MLF
  5. to LEFT CN3
    - —-> contralateral saccades
30
Q

What neurons prevent unwanted saccades?

A

Inhibitory pause neurons

31
Q

Follow the path from the visual cortex to produce a saccade…. describe the contribution of the rest of the cortex in this.

A
  1. Visual cortex
  2. PEF
  3. PRE frontal eye field (dorsolateral prefrontal cortex - memories of saccades)
    + Supplementary eye field
  4. FEF
  5. SC
  6. PPRF
32
Q

What is the PEF involved in?

A

Position of the object identification

33
Q

What does smooth pursuit do?

A

Matches Target velocity to eye velocity

34
Q

What does the VOR match?

A

Matches head velocity to eye velocity

35
Q

What do saccades match?

A

Eye position to target position

36
Q

To generate rightward pursuit….. describe the path from the right Parietotemporal junction

A
  1. Right parietotemporal junction provides velocity info to
  2. Right FEF
  3. Ipsilateral rightward pursuit
  4. to RIGHT pons
  5. left cerebellum/left vestibular
  6. left brainstem and crosses to right abducens
    RIGHT FEF - RIGHT ABDUCENS
37
Q

Why are vergence movements slower than saccades?

A

ciliary muscles for accommodation are slow

38
Q

Which reflex are vergence movements related to?

A

Accommodation reflex

39
Q

Saccades VOR have Contralateral effects… but what has ipsilateral effects…

A

Smooth pursuit

40
Q

Eyes typically deviate towards…

A

SAME side of the lesion - AWAY from hemiparetic side

41
Q

Pontine lesions result in…

A

Eyes deviating AWAY from the lesion (towards the hemiparesis)

42
Q

A right cerebral cortical lesion will result in…

A
  1. Right frontal lobe damage
  2. Left hemiparesis
  3. gaze to the right (unopposed left FEF)
43
Q

A lesion in the right pons will result in

A
  1. Left hemiparesis

2. Leftward gaze

44
Q

If you have someone with horizontal gaze palsy (cant look to left)… what are two possible reasons for that?

A
  1. lesion could be in right FEF

2. or Left pons

45
Q

what happens with a left MLF lesion

A
  1. when you look right, left eye cannot adduct
  2. Nystagmus in the abducting eye
  3. Convergence is intact
46
Q

What is one reason for upgaze palsy?

A

Dorsal midbrain lesion

47
Q

In nystagmus if the fast phase is towards the left…..

A

it is left horizontal nystagmus

48
Q

3 symptoms of nystagmus

A
  1. Blurred vision
  2. Oscillopsia
  3. Unsteady gait
49
Q

What do aminoglycosides - antibiotics do to VOR?

A

toxic to inner ear - knock out VOR - cant recognize faces - have to keep eyes perfectly still.

50
Q

Which responds faster the VOR or Pursuit?

A

VOR responds faster than pursuit

51
Q

Saccades also have a phasic burst and a tonic phase

A

Direct path mediates phasic command - PULSE

The tonic phase is still mediated by the NPH to hold eyes in position - STEP

52
Q

What supplementary parts of the cortex are involved in saccades

A

goes to PEF - tracks where, FEF tells brainstem to move the eye

  1. supplementary eye field (learned sequences of saccades)
  2. Dorsolateral prefrontal cortex (memories of objects/saccades and decisions, delay a saccade or other)
53
Q

What does the parieto-temporal junction provide?

A

VELOCITY information - remember pursuit

54
Q

Nystagmus lesions often occur …

A
  1. Inner ear
  2. Brainstem
  3. Cerebellum

Neuroanatomy 2 (25 decks)

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