Physiology of saccades and fixation in peripheral gaze

Question 1

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

Answer 1

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

Felderstruktur fivres - 20% - smaller tonic contraction

Question 2

What is the white stuff in the cytoplasm?

Answer 2

Myofilaments

Question 3

What type of eye movement is needed for peripheral vision?

Answer 3

Large saccades

Question 4

What type of eye movement is needed for central vision?

Answer 4

Small saccades

Question 5

What do saccades require?

Answer 5

Fast muscle contractioninvolving fibrillenstrucktur fibres to rapidly move eyes

Question 6

How are saccades mediated by?

Answer 6

Saccade generator nuclei (PPRF, riMLF)

Question 7

What do peripheral fixation require?

Answer 7

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

Question 8

How are peripheral saccades mediated?

Answer 8

From brainstem by neural integrator nuclei

Question 9

What are neural integrator nuclei for?

Answer 9

For horizontal and vertical gaze holding

Question 10

What nuclei is needed for horizontal and vertical gaze holding?

Answer 10

Neural Intergrator nuclei

Question 11

What neural intergrator nuclei is needed for Horizontal gaze holding?

Answer 11

PeriHypoglossal nucleus (PHN)

Question 12

What is another name for PHN?

Answer 12

Nucleus Prepositus hypoglossi nucleus

Question 13

What neural intergrator nuclei is needed for vertical gaze holding?

Answer 13

Intersitial nuclei of cajal (INC)

Question 14

Where is the PHN found?

Answer 14

In medulla, below abducens nucleus

Question 15

Where is INC found?

Answer 15

Upper midbrain, above oculomotor complex

Question 16

How to EBC fire ?

Answer 16

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

Question 17

What does their firing duration determnine of EBC?

Answer 17

Amplitude of saccades

Question 18

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

Answer 18

Faster and larger saccades

Question 19

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

Answer 19

Smaller saccades

Question 20

How is eye drifting back to primary gaze a problem?

Answer 20

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

Question 21

What if you get a lesion in NPH or INC?

Answer 21

Failure to hold eccentric gaze

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

Question 22

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

Answer 22

Nystagmus

Question 23

How are saccades controlled?

Answer 23

Omni pause cells

Question 24

Where are pause cells located?

Answer 24

Midline near PPRF and abducent nucleus in Nucleus Raphe interpositus

Question 25

What do pause cells do?

Answer 25

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

Question 26

What can NRI lesions cause?

Answer 26

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

Question 27

What can NRI cause ?

Answer 27

Blindness

Question 28

What are higher saccades control centres for?

Answer 28

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

Question 29

Where is the PEF located?

Answer 29

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

Question 30

Where is FEF located?

Answer 30

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

Question 31

Where is SEF located?

Answer 31

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

Question 32

Why nuclei is responsible for horizontal saccades?

Answer 32

Peri hypoglossal nucleus