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Sophie - The Nervous System - Year 2 > 21.7 Eye movement control and Pupillary Reflexes > Flashcards

21.7 Eye movement control and Pupillary Reflexes Flashcards

1
Q

What are the different CNs involved in eye movement control and pupillary reflexes?

A

CN3, CN4, and CN6

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2
Q

What are the main types of eye movement you need to know about?

A

To bring the image of a target onto the fovea:

  • Saccades
  • Vergence

To keep the image on the fovea:

  • Smooth pursuit (during target movement)
  • Vestibulo-ocular (during head movement)
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3
Q

What are saccadic eye movements (a.k.a. saccades)?

[IMPORTANT]

A

Rapid, ballistic movements where eyes abruptly change point of fixation
e.g. scanning faces

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4
Q

What are the five types of saccades?

A

Reflexive (prosaccades) - e.g. following jumping dot on screen
Voluntary - e.g. scanning around a room, predicting movement of a target
Spontaneous - gaze shift away from a fixed point (unconscious)
Microsaccades - unconscious tiny movements of eyes
Quick phases - e.g. in nystagmus

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5
Q

What is vergence?

[IMPORTANT]

A

Alignment of the fovea with objects at different distances (cross eyed/eyes apart)

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6
Q

What is smooth pursuit?

[IMPORTANT]

A

When the eyes remain fixed on a moving object

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7
Q

What is the vestibulo-ocular eye movement?

[IMPORTANT]

A

When the eyes are stabilised on an object despite the head moving

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8
Q

What are the signs of lesion of the oculomotor nerve?

A
  • Down and out position of eye at rest
  • Ptosis (usually innervates levator palpabrae superioris - raises upper eyelid)
  • Dilated pupil (usually innervates sphincter pupillae - constricts pupil)
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9
Q

What are the signs of lesion of the trochlear nerve?

A
  • Diplopia when looking down and inwards
  • Head tilt away from affected side (compensation)
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10
Q

What are the signs of lesion of the abducens nerve?

A
  • Diplopia when looking to side
  • Affected eye resting in adduction (looking inwards)
  • Inability to abduct eye
  • Rotate head to allow eye to look sideways (compensation)
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11
Q

What are the three brainstem nuclei involved in eye movements?

A

Oculomotor nucleus
Trochlear nucleus
Abducens nucleus

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12
Q

Where is the oculomotor nucleus located?

A

Midbrain, at level of mesencephalic reticular formation

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13
Q

Where is the trochlear nucleus located?

A

In midbrain, slightly caudal to oculomotor nucleus

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14
Q

Where is the abducens nucleus located?

A

In pons, at level of paramedian pontine reticular formation. Also adjacent to fasciculus of facial nerve (VII)

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15
Q

Where do the neuronal signals for saccades originate in the brain?

A

Reticular formation

Vertical saccades = mesencephalic reticular formation (MRF)
Horizontal saccades = paramedian pontine reticular formation (PPRF)

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16
Q

What are the MRF and PPRF also known as?

A

Gaze control centers

17
Q

What is the connective role of the medial longitudinal fasciculus?

A

Links superior colliculus, oculomotor nuclei and vestibular nuclei with gaze control centres (in reticular formation)

18
Q

What is the key structure through which the cerebral cortex controls saccades?

A

Superior colliculus

19
Q

What are the three cortical inputs that the superior colliculus receives? Are they excitatory or inhibitory?

A

Excitatory from posterior parietal cortex
Excitatory from frontal eye fields
Inhibitory from substantia nigra

20
Q

What is the process in which the inhibitory substantia nigra can be itself inhibited? (so that its inhibition is released)

A

Frontal eye field excites caudate nucleus
Caudate nucleus inhibits substantia nigra

21
Q

What is the role of the vestibular nuclei in eye movement?

A

They help coordinate antagonist muscles involved in eye movement of smooth pursuit and vestibulo-ocular reflexes

22
Q

What does the vestibular nuclei provide its input to?

A

Abducens, trochlear, oculomotor nuclei

23
Q

What are the higher cortical areas that signal to the vestibular nuclei called?

A

Medial superior temporal gyrus/middle temporal gyrus (MST/MT)
Frontal eye field

24
Q

What is the function of the pupillary light reflex?

A

To adjust the size of the pupil at different light levels

25
Q

The pupillary light reflex is consensual - what does this mean?

A

Light directed in one eye produces pupil constriction in both eyes

26
Q

Which two antagonistic muscle fiber types control pupil size?

A

Sphincter, dilator

27
Q

Which branches of the autonomic system are the sphincter and dilator muscle fibres each controlled by?

A

Sphincter: parasympathetic
Dilator: sympathetic (think - need to see more for dangerous situations)

28
Q

Which muscle fibre usually dominates in the pupillary light reflex?

A

Sphincter

29
Q

Describe the first step of the pupillary light reflex when light hits an eye/both eyes.

A

Light signal sent through optic nerve(s) to pretectal nuclei of midbrain

30
Q

Describe the second step in the pupillary light reflex after signal is sent to pretectal nuclei.

A

Pretectal nuclei BILATERALLY innervate the Edinger-Westphal nuclei of the oculomotor complex, through posterior commissure

31
Q

Describe the third step in the pupillary light reflex after the signal is sent to the Edinger-Westphal nuclei.

A

Edinger-Westphal nuclei send oculomotor preganglionic parasympathetic fibres to ciliary ganglion

32
Q

Describe the fourth (final) step in the pupillary light reflex after the signal is sent to the ciliary ganglion.

A

Ciliary ganglion sends signal via short ciliary nerve to iris sphincter; pupil constricts.

33
Q

What is the definition of the accommodation reflex?

A

The changes in the eye when viewing a near object to bring it into focus

34
Q

Which 3 motor responses occur in the accommodation (near) reflex?

A
  • Eye gaze moves to be more medial/’cross-eyed’ (vergence) as medial rectus contracts
  • Lens gets fatter as ciliary muscles contract
  • Pupil constricts as iris sphincter contracts
35
Q

What is the pathway of the afferent limb of the accommodation reflex?

A
  • Retina
  • LGN
  • Visual cortex
36
Q

What are the two components of the efferent limb of the accommodation reflex?

A
  • Edinger-Westphal nucleus (parasympathetic) –> ciliary ganglion –> iris sphincter, ciliary muscle
  • Oculomotor neurons –> medial rectus
37
Q

What is the cause of Horner’s syndrome?

A

Lesion of sympathetic supply to eye/face

38
Q

What is the mechanism for partial ptosis occurring in Horner’s syndrome?

A

There is a lesion to the sympathetic supply to levator palpebrae superioris so the eyelid cannot be held up.

39
Q

Does Horner’s syndrome make the affected pupil constrict or dilate?

A

Constrict
(as cannot do normal sympathetic dilation)

Sophie - The Nervous System - Year 2 (46 decks)

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