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BV simon > Physiology of saccades and fixation in peripheral gaze > Flashcards

Physiology of saccades and fixation in peripheral gaze Flashcards

1
Q

What 2 principle muscle fibres do the rectus and oblique have?

A

Fibrillenstrucktur fibres - 80% total - large active fast phasic contract ion

Felderstruktur fivres - 20% - smaller tonic contraction

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2
Q

What is the white stuff in the cytoplasm?

A

Myofilaments

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3
Q

What type of eye movement is needed for peripheral vision?

A

Large saccades

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4
Q

What type of eye movement is needed for central vision?

A

Small saccades

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5
Q

What do saccades require?

A

Fast muscle contractioninvolving fibrillenstrucktur fibres to rapidly move eyes

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6
Q

How are saccades mediated by?

A

Saccade generator nuclei (PPRF, riMLF)

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7
Q

What do peripheral fixation require?

A

sustained contraction by felderstrucktur fibres to prevent eyes from drifting and hold steady gaze for periods of fixation and object inspection

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8
Q

How are peripheral saccades mediated?

A

From brainstem by neural integrator nuclei

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9
Q

What are neural integrator nuclei for?

A

For horizontal and vertical gaze holding

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10
Q

What nuclei is needed for horizontal and vertical gaze holding?

A

Neural Intergrator nuclei

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11
Q

What neural intergrator nuclei is needed for Horizontal gaze holding?

A

PeriHypoglossal nucleus (PHN)

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12
Q

What is another name for PHN?

A

Nucleus Prepositus hypoglossi nucleus

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13
Q

What neural intergrator nuclei is needed for vertical gaze holding?

A

Intersitial nuclei of cajal (INC)

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14
Q

Where is the PHN found?

A

In medulla, below abducens nucleus

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15
Q

Where is INC found?

A

Upper midbrain, above oculomotor complex

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16
Q

How to EBC fire ?

A

High frequency up to 1000HZ for brief seconds 10-15msec before saccades begin

17
Q

What does their firing duration determnine of EBC?

A

Amplitude of saccades

18
Q

What does higher frequency and longer duration burst of EBC result in?

A

Faster and larger saccades

19
Q

What does lower frequency and shorter duration burst of EBC result in?

A

Smaller saccades

20
Q

How is eye drifting back to primary gaze a problem?

A

Elastic restoring forces of orbital connective tissue supporting the eye causes it to drift back to primary gaze position

21
Q

What if you get a lesion in NPH or INC?

A

Failure to hold eccentric gaze

effected eye drifts back to primary position with new saccades to re fixate the target of interest

22
Q

What manifest deviation can you get with lesions in NPH OR INC?

A

Nystagmus

23
Q

How are saccades controlled?

A

Omni pause cells

24
Q

Where are pause cells located?

A

Midline near PPRF and abducent nucleus in Nucleus Raphe interpositus

25
Q

What do pause cells do?

A

Fire continuously to tonically inhibit excitatory burst cells in PPRF and riMLF

26
Q

What can NRI lesions cause?

A

Opsoclonus -saccades in random direction with no pause cells for fixation

27
Q

What can NRI cause ?

A

Blindness

28
Q

What are higher saccades control centres for?

A
  1. Visually cured , reflexive saccades
    - Midbrain : Superior colliculus
    - Posterior cerebral cortex: Parietal eye field
  2. Internally generated, voluntary saccades
    - Frontal cerebral cortex : Frontal eye field and supplementary eye field
29
Q

Where is the PEF located?

A

Parietal eye field - Inferior parietal lobule - below intra parietal sulcus within brodmann area 39 & 40

30
Q

Where is FEF located?

A

Frontal eye field- Posterior end of middle frontal gyrus -infront of primary motor cortex within brodmann area 6

31
Q

Where is SEF located?

A

Supplementary eye field - posterior end of superior frontal gyrus above FEF within brodmann areas 6 & 8

32
Q

Why nuclei is responsible for horizontal saccades?

A

Peri hypoglossal nucleus

BV simon (5 decks)

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