Reflex and voluntary saccades

Question 1

What are supra nuclear used for?

Answer 1

Higher centres

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

Question 2

What happens generator do in supra nuclear?

Answer 2

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

Question 3

What happens in the inter nuclear pathway?

Answer 3

Medial longitudinal fasciculus to ocular motar neurones

Question 4

What happens in ocular motor neurones?

Answer 4

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

Question 5

What are saccades?

Answer 5

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

Question 6

How can saccades occur?

Answer 6

Reflexive (Visually cued)

Voluntary (internally generated)

Question 7

What is reflexive saccades?

Answer 7

> Express to novel stimulus

>When scanning an object of interest

Question 8

What is voluntary saccades?

Answer 8

Cognitively or memory guided

Question 9

What brainstem generators are activated for saccades?

Answer 9

PPRF- paramedian pontine reticular formation

riMLF - rostral interstitual nucleus of medial longitudinal fasciculus

Question 10

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

Answer 10

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

Question 11

What do superficial layers receive?

Answer 11

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

Question 12

What is the map of opposite hemiffield?

Answer 12

Centre to peripheral VF- anterior to posterior SC

Lower to upper VF, Lateral to medial SC

Question 13

What are superficial neurones connected to ?

Answer 13

Deeper layers

Question 14

What do the deeper layers contain?

Answer 14

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

Question 15

What projections do deep layers do to the PPRF?

Answer 15

Crossed projections to PPRF - horizontal saccades generator

Question 16

What projections do the deep layers make to riMLF ?

Answer 16

Bilateral projections to the riMLF - the vertical saccade generator

Question 17

What does unilateral lesion to superior colliculus cause?

Answer 17

Abolish reflexive express saccades into the opposite hemi field

Question 18

How many scanning saccades do we make in a day?

Answer 18

250,000 every day

Question 19

?What is purpose of saccades?

Answer 19

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

So acquiring more detailed knowledge about them

Question 20

What does PEF recieve?

Answer 20

Direct inputs from Dorsal stream Extra staita areas

Question 21

Where does PEF project ?

Answer 21

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

Question 22

How does PEF send axons to deep layer neurones?>

Answer 22

Via the internal capsule of posterior limb

Question 23

What does it allow PEF to do?>

Answer 23

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

Question 24

What does unilateral lesions to PEF cause?

Answer 24

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

Question 25

What is the descending projects from PEF?

Answer 25

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

Question 26

What is the descending projects from Internal capsule?

Answer 26

Posterior portion:Axon in white matter

Question 27

What is the descending projects from Cerebral peduncle?

Answer 27

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

Question 28

What does right lesion of PEF cause ?

Answer 28

Reduced scanning and neglect in the left hemi field

Question 29

How do you get voluntary saccades ?

Answer 29

Because you decide to look at something different Because you are instructed to look at this

Question 30

What are voluntary saccades influenced by>?

Answer 30

Cognative factors | >You want to inspect something specific

Question 31

What are volunatry saccades executed as?

Answer 31

Scanning across words on page while reading

Question 32

What does frontal eye field mediate?

Answer 32

Initiates all self generated saccades

Question 33

How are self generated saccades initiated?

Answer 33

Via direct projections to the brainstem saccade generators

Question 34

How does self generated axons run?

Answer 34

Descending axons run in the internal capsule then cerebral peduncle

Question 35

How does elf generated saccades project to PPRF ?

Answer 35

Cross over to the PPRf and go bilaterally to riMLF

Question 36

What does each FEF contain?

Answer 36

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

Question 37

What does unilateral lesion to FEF cause?

Answer 37

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

Question 38

What is the descending projections from the FEF?

Answer 38

From FEF to PPRF axons cross in the upper pons for horizontal To riMLF, bilateral for straight up or down

Question 39

What does left FEF lesion cause ?

Answer 39

Right gaze palsy

Question 40

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

Answer 40

Via dense inter cortical projections

Question 41

How does FEF & SEF also have another connection ?

Answer 41

Direct descending projections to the deep layers of the superior colliculus

Question 42

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

Answer 42

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

Question 43

How are cerebellar cortex and deep nuclei involved in saccades?

Answer 43

Gain control

Question 44

How do the cerebellar cortex and deep nuclei function as ?

Answer 44

Common supervisor

Question 45

What is activated during voluntary and reflex saccade pathway?

Answer 45

Activates brainstem generators PPRF and riMLF