Eye and Head Movements Flashcards Preview

MD1 Neuroscience > Eye and Head Movements > Flashcards

Flashcards in Eye and Head Movements Deck (55):
1

What are the two components for the control of gaze?

Oculomotor system
Head-movement system

2

What does the oculomotor system control?

Moves eyes in orbit while head is still

3

What structures does the oculomotor system include?

Extraocular muscles
Neural pathways coordinating movement of each eye

4

What does the head-movement system control?

Moves eye sockets as a whole while head moves

5

What structures does the head-movement system include?

Vestibular system
Oculomotor system

6

What are saccadic eye movements?

Shifts fovea rapidly to new visual target

7

What are smooth pursuits?

Keeps image of moving target on fovea

8

What is vergence?

Moves eyes in opposite directions
- Convergence = going cross-eyed
- Divergence impossible

9

What are vestibular ocular movements?

Holds image still on retina during brief head movements

10

What are optokinetic movements?

Holds image stationary during sustained head rotation/translation

11

How many extraocular muscles are there?

6

12

What are the rectus muscles?

Superior rectus
Inferior rectus
Medial rectus
Lateral rectus

13

What are the oblique muscles?

Inferior oblique
Superior oblique

14

Which muscle does superior oblique go underneath?

Superior rectus

15

Which muscle does inferior oblique go near?

Inferior rectus

16

What kinds of actions do extraocular muscles have?

Primary
Secondary
Sometimes tertiary

17

What is the primary action of superior rectus?

Elevation

18

What is the primary action of inferior rectus?

Depression

19

What is the primary action of medial rectus?

Adduction

20

What is the primary action of lateral rectus?

Abduction

21

Where do the rectus muscles insert?

At equator

22

Where does the superior oblique insert?

Well behind equator at oblique angle close to lateral rectus

23

Through which structure does the tendon of the superior oblique run?

Trochlea

24

What is the primary action of superior oblique?

Torsion - down and in

25

Where does the inferior oblique insert?

Behind equator close to lateral rectus

26

What is the primary action of inferior oblique?

Torsion - up and out

27

Which muscles elevate and depress the eye when it is adducted?

Elevate = inferior oblique
Depress = superior oblique

28

Which muscles elevate and depress the eye when it is abducted?

Elevate = superior rectus
Depress = inferior rectus

29

What does the hierarchical control of eye movements involv?

LMNs = cranial nerves
Brainstem eye movement centres = reticular formation
Higher cortical area = frontal eye fields

30

Where are the frontal eye fields?

Near motor cortex

31

Which muscles are innervated by the oculomotor nerve?

Superior rectus
Inferior rectus
Medial rectus
Inferior oblique

32

Which muscles are innervated by the trochlear nerve?

Superior oblique

33

Which muscles are innervated by the abducens nerve?

Lateral rectus

34

What is the medial longitudinal fasciculus (MLF)?

White matter tract > connects various cranial nerve nuclei

35

Which cranial nerve nuclei does the MLF especially connect?

III
IV
VI
VIII

36

What is the reticular formation?

Coordinates action of nuclei controlling eye movements

37

What are the two reticular formations?

Pontine paramedian reticular formation
Mesencephalic paramedian reticular formation

38

What does the pontine paramedian reticular formation control?

Horizontal gaze centre
Coordination of medial rectus and lateral rectus of each eye
Coordination of CN III and CN VI

39

What does the mesencephalic paramedian reticular formation control?

Vertical gaze centre
Coordination of superior oblique and superior rectus of each eye
Coordination of CN III and CN IV

40

What are burst neurons?

Fire at high frequency just before movement
Excitatory connections with ipsilateral abducens
Inhibitory connections suppress activity of contralateral abducens

41

What are omnipause neurons?

Fire continuously except during saccade
GABAergic
Project to contralateral abducens nucleus

42

What is needed for neural control of saccades?

Simultaneous excitation of burst neurons and inhibition of omnipause neurons

43

What is the sequence of events for the horizontal neural control of saccades?

1. Frontal eye fields send signal
2. Ipsilateral excitatory burst neurons in PPRF depolarises
3. Excitatory synapse in ipsilateral abducens nucleus
4. Ipsilateral CN VI sends signal
5. Lateral rectus contracts
6. MLF sends signal from ipsilateral abducens nucleus to contralateral oculomotor nucleus
7. Contralateral CN III sends signal
8. Medial rectus contracts
9. Ipsilateral inhibitory burst neurons in PPRF send signal
10. Contralateral abducens nucleus inhibited
11. Contralateral CN VI inhibited
13. Contralateral lateral rectus relaxes
14. MLF sends signal from contralateral abducens nucleus to ipsilateral oculomotor nucleus
15. Ipsilateral oculomotor nucleus inhibited
16. Ipsilateral oculomotor nerve inhibited
17. Ipsilateral medial rectus relaxes

44

What are eye movements ultimately driven by?

Behaviour

45

Which upper motor neurons drive brainstem gaze centres?

Frontal eye fields
Posterior parietal cortex
Superior colliculus
Basal ganglia

46

In which direction do frontal eye fields control saccades?

Contralateral direction

47

What happens when there is a lesion in the medial longitudinal fasciculus?

Internuclear ophthalmoplegia

48

What provides information about the position of the head in space?

Vestibular system

49

What is the role of the vestibular system in controlling eye movements?

Coordinates position of head and eyes

50

What structure gives information about head position?

Semicircular canals

51

What structure gives information about linear acceleration?

Otolith organs
- Saccule
- Utricle

52

How do the vestibular sensory receptors work?

Crystals and fluid inside vestibule over hair cells
Hair cells have cilia
Move head > move fluid > move cilia
Hair cells depolarise or hyperpolarise

53

With which cranial nerves does the vestibulocochlear nerve communicate to coordinate eye movements when the head moves in the horizontal plane?

CN III and VI

54

Which nucleus receives vestibular information?

Vestibular nuclei in medulla

55

Describe the vestibular ocular reflex when you turn your head to the left?

Left horizontal semicircular canal senses left movement
1. CN VIII carries info to left vestibular nucleus
2. Excitatory signal from vestibular to abducens nucleus
3. Right lateral rectus contracts
4. Left MLF sends signal from right abducens nucleus to left oculomotor nucleus
5. Left medial rectus contracts
6. Left vestibular nucleus also sends signal to left oculomotor nucleus
7. Left lateral rectus and right medial rectus relax

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