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BV simon > Reflex and voluntary saccades > Flashcards

Reflex and voluntary saccades Flashcards

1
Q

What are supra nuclear used for?

A

Higher centres

  • Initial eye movements for different purpose
  • send motor commands to the relevant brainstem generator
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2
Q

What happens generator do in supra nuclear?

A

Activates burst cells which fire particular patterns of activity sent via axons in the inter nuclear pathway

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3
Q

What happens in the inter nuclear pathway?

A

Medial longitudinal fasciculus to ocular motar neurones

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4
Q

What happens in ocular motor neurones?

A

Activating ocular motor neurones and causing similar firing patterns
-Required for contraction of their EOM

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5
Q

What are saccades?

A

Fast conjugate re directions of bi foveal gaze up to 1000 deg/s

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6
Q

How can saccades occur?

A

Reflexive (Visually cued)

Voluntary (internally generated)

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7
Q

What is reflexive saccades?

A

> Express to novel stimulus

>When scanning an object of interest

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8
Q

What is voluntary saccades?

A

Cognitively or memory guided

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9
Q

What brainstem generators are activated for saccades?

A

PPRF- paramedian pontine reticular formation

riMLF - rostral interstitual nucleus of medial longitudinal fasciculus

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10
Q

What 5 higher control centres are for fast saccadic eye movements?

A

> > Frontal eye field (FEF)+SEF( Supplimentary eye field)
Parietal eye field (PEF)
Midbrain superior colliculus (SC)
Midline Cerebellar cortex and nuclei

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11
Q

What do superficial layers receive?

A

Receive direct retinal inputs and contain maps of opposite visual hemifield?

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12
Q

What is the map of opposite hemiffield?

A

Centre to peripheral VF- anterior to posterior SC

Lower to upper VF, Lateral to medial SC

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13
Q

What are superficial neurones connected to ?

A

Deeper layers

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14
Q

What do the deeper layers contain?

A

Pre motor neurones and a map of saccade directions, in register with the visual map in the layers above
>Centre to peripheral gaze -anterior to posterior SC
>Down to up gaze - lateral to medial SC

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15
Q

What projections do deep layers do to the PPRF?

A

Crossed projections to PPRF - horizontal saccades generator

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16
Q

What projections do the deep layers make to riMLF ?

A

Bilateral projections to the riMLF - the vertical saccade generator

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17
Q

What does unilateral lesion to superior colliculus cause?

A

Abolish reflexive express saccades into the opposite hemi field

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18
Q

How many scanning saccades do we make in a day?

A

250,000 every day

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19
Q

?What is purpose of saccades?

A

To examine different regions of interest on objects by bo fixating them with our high acuity foveas

So acquiring more detailed knowledge about them

20
Q

What does PEF recieve?

A

Direct inputs from Dorsal stream Extra staita areas

21
Q

Where does PEF project ?

A

Sends descending projections to deep layers neurones in saccade map of ipsilateral SC

22
Q

How does PEF send axons to deep layer neurones?>

A

Via the internal capsule of posterior limb

23
Q

What does it allow PEF to do?>

A

Issue commands to these SC neurones and hotwire their direct access to the brainstem saccade generators

24
Q

What does unilateral lesions to PEF cause?

A

Contralateral hemi- spatial neglect or improverished scanning in the opposite hemi field (Sticky fixation)

25
Q

What is the descending projects from PEF?

A

PEF: Premotor neurone ell body in gray mattar of inferior parietal lobule

26
Q

What is the descending projects from Internal capsule?

A

Posterior portion:Axon in white matter

27
Q

What is the descending projects from Cerebral peduncle?

A

Axon in white matter will exit and travel to deep layers of SC

28
Q

What does right lesion of PEF cause ?

A

Reduced scanning and neglect in the left hemi field

29
Q

How do you get voluntary saccades ?

A

Because you decide to look at something different

Because you are instructed to look at this

30
Q

What are voluntary saccades influenced by>?

A

Cognative factors

>You want to inspect something specific

31
Q

What are volunatry saccades executed as?

A

Scanning across words on page while reading

32
Q

What does frontal eye field mediate?

A

Initiates all self generated saccades

33
Q

How are self generated saccades initiated?

A

Via direct projections to the brainstem saccade generators

34
Q

How does self generated axons run?

A

Descending axons run in the internal capsule then cerebral peduncle

35
Q

How does elf generated saccades project to PPRF ?

A

Cross over to the PPRf and go bilaterally to riMLF

36
Q

What does each FEF contain?

A

A map of saccades directions, mainly towards the opposite side of hemifield

37
Q

What does unilateral lesion to FEF cause?

A

Ablish voluntary saccades away from affected side (Paralysis of conta -versive gaze)

38
Q

What is the descending projections from the FEF?

A

From FEF to PPRF axons cross in the upper pons for horizontal

To riMLF, bilateral for straight up or down

39
Q

What does left FEF lesion cause ?

A

Right gaze palsy

40
Q

How are PEF and SEF connected to each other and other ispilateral PEF?

A

Via dense inter cortical projections

41
Q

How does FEF & SEF also have another connection ?

A

Direct descending projections to the deep layers of the superior colliculus

42
Q

What does the descending projections to deep layers of superior colliculus do?

A

They inhibit the deep layer neurones , preventing the occurrence of unwanted express saccades during more purposeful voluntary visual search

43
Q

How are cerebellar cortex and deep nuclei involved in saccades?

A

Gain control

44
Q

How do the cerebellar cortex and deep nuclei function as ?

A

Common supervisor

45
Q

What is activated during voluntary and reflex saccade pathway?

A

Activates brainstem generators PPRF and riMLF

BV simon (5 decks)

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