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B3 CAI > Eyes: Reflexes and Movements > Flashcards

Eyes: Reflexes and Movements Flashcards

1
Q

The pupils should normally show a ? and ? reflex to light and both should respond equally. Deviation indicates pathology.

A

direct, consensual

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2
Q

Why is a unilateral lesion to the posterior part of the brainstem unlikely to result in a loss of consensual or direct pupil light reflex?

A

The neurons within the pupillary light reflex pathway are distributed bilaterally at several points within the brainstem.

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3
Q

However, damage to an ? nucleus or ? will result in a loss of pupillary light reflex on the ipsilateral side.

A

Edinger-Westphal, CN III

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4
Q

What is a relative afferent pupillary defect (Marcus-Gunn pupil)?

A

Examination finding in patients who have an asymmetric pupillary reaction to light when it is shined back and forth between the two eyes.

Most commonly a sign of asymmetric optic nerve disease or damage but can also present in widespread asymmetric retinal disease.

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5
Q

After exiting the ventral surface of the midbrain, CN III can be damaged by {{c1::compression}} or by {{c1::infarction}}, with each one having different effects.

A

compression,

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6
Q

What does a complete CN III lesion result in?

A

No direct or consensual reflex on the damaged side – the pupil is dilated and unreactive plus, the eye is abducted and depressed and the eyelid closed (ptosis)).

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7
Q

Which two extraocular muscles are not innervated by CN III?

A

Lateral rectus (CN VI) and superior oblique (CN IV).

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8
Q

Eyelids show ptosis due to loss of innervation to what muscle?

A

Levator palpebrae superioris.

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9
Q

How do examination findings associated with a compressive lesion of CN III differ to those of an infarction/ vascular lesion?

A

Compression of CN III will result in a loss of all functions of CN III e.g. aneurysm or tumour.

A vascular lesion will spare pupillary functions.

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10
Q

Why are pupillary functions spared in vascular lesions of CN III?

A

Due to the position the parasympathetic nerves sit within CN III.

Sit in a superficial position on the nerve so will receive a different blood supply to the deeper sections of the nerve (parts innervating the extraocular muscles).

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11
Q

An ? pupil shows no pupillary light reflex but the accommodation reflex response is normal.

A

Argyll-Robertson

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12
Q

Damage associated with Argyll-Robertson pupil has occurred in what part of the brain?

A

Posterior aspect of the midbrain.

Damage affects the pretectal nuclei and the neurons between them.

EW nucleus is still functional.

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13
Q

Are the Edinger-Westphal nuclei only innervated by the pretectal nuclei?

A

No, innervated by a range of different pathways.

Neurons from different cortical areas such as the frontal eye field (this is why the accommodation response is maintained when the pretectal nucleus is damaged).

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14
Q

What conditions may cause an Argyll-Robertson pupil occur?

A

Diabetic neuropathy, encephalitis, multiple sclerosis, alcoholism and tertiary neurosyphilis (rare).

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15
Q

The eye can rotate around ? mutually perpendicular axes.

A

three

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16
Q

What movement does each axis allow?

A

Black: allows eye to adduct (medial) and abduct (lateral).

Red: allows elevation (up) and depression (down).

Blue: allows intorsion (twisting in) and extorsion (twisting out).

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17
Q

Corrective action (intorsion/extorsion) when you move your head is brought about by the ?.

A

Vestibulo-ocular reflex

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18
Q

Are the axes of the eyeball and the orbit aligned with eachother?

A

No, cannot be aligned.

If they were aligned, the superior and inferior rectus muscles would only elevate and depress the eyebrall from the primary positions.

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19
Q

The medial wall of the orbit is aligned relatively parallel to the ?, resulting in the long axis of the orbit facing anterolaterally.

A

medial sagittal plane

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20
Q

In their primary position, where do the eyeballs face?

A

Anteriorly.

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21
Q

Why is an H-shaped pattern of movements used to test eye movement?

A

It isolates the vertical actions brought about by specific muscles (not usd by all clinicians).

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22
Q

Apart from the H-shaped pattern of movements, what can be used to test eye movements?

A

Cardinal positions of gaze of the left and right in six directions.

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23
Q

The testing of SO, IO, SR and IR muscles aligns the ? of the muscle being tested with the axis of a specific movement (elevation or depression). This means only that muscle is able to bring about the movement.

A

tendon

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24
Q

Which muscles rotate the eye around the black axis?

A

Lateral rectus and medial rectus muscles.

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25
Q

What is conjugation of gaze?

A

Both eyes moving in the same direction, at the same speed, at the same time.

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26
Q

If only the superior rectus muscle were to contract, what direction would the eye move in?

A

Elevated and adducted.

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27
Q

If only the inferior rectus muscle were to contract, what direction would the eye move in?

A

Depressed and adducted.

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28
Q

When the inferior oblique muscle contracts, it pulls the ? part of the eyeball anteriorly, rotating the and elevating the eyeball.

A

posterolateral

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29
Q

How do you test the elevation action of superior rectus by itself and how do you test the depression action of inferior rectus by itself?

A

Same for both.

First change the initial position of the eye into an abducted position using LR muscle (in this position, the SR muscle will be crossing over the axis of rotation).

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30
Q

Which two muscles depress the eyeball?

A

Inferior rectus and superior oblique.

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31
Q

Which two muscles elevate the eyeball?

A

Superior rectus and inferior oblique.

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32
Q

How do you test the depression of superior oblique and how do you test elevation of inferior oblique?

A

First use medial rectus to adduct the eye.

In this adducted position, IR still crosses the red axis but is running much more parallel to the red axis.

Therefore, IR is a weak depressor of the eye from this position, leaving SO or IO as the prime depressor.

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33
Q

Testing the eyes using the cardinal positions of gaze test involves moving the eyes ?, relying on a combination of muscles.

A

diagonally

34
Q

What is Hering’s Law?

A

The extraocular muscles normally have equal and simultaneous innervation, thus permitting conjugate movement.

35
Q

Pathologies that upset the equal and simultaneous innervation can affect conjugate eye movements which, in turn, can result in what?

A

diplopia

36
Q

What is the medial longitudinal fasciculus?

A

An interneuron tract that connects the nuclei of CN III, IV and VI.

Involved in bringing about conjugate eye movements.

37
Q

What are the three ways the eyes can move?

A
  • Can track a target – smooth pursuit when the target is moving and you are still.
  • Scan from target to target (Saccadic) – scanning between targets.
  • Vestibulo-ocular reflex – Stabilise gaze during head movement.
38
Q

Multiple different control centres can influence the movement of the eyes; name some of them.

A
  • Vestibular nuclei.
  • Parapontine reticular formation.
  • Frontal eye field (frontal cortex).
  • Saccade centres (several locations).
  • Visual association areas.
  • Cerebellum.
39
Q

MLF is also associated with bringing about tracking movements of the ? at the same time as the eyes.

A

Neck

40
Q

To enable both eyes to look either left or right at the same time and by the same amount, we need to simultaneously activate a given ? with the contralateral ?.

A

CN VI nucleus, CN III nucleus

41
Q

The MLF contains many interneurons that will interconnect the nuclei of CN ? and ?.

A

III, VI

42
Q

How does the MLF bring about movements of the neck?

A

Descends through the brainstem and into the proximal spinal cord.

43
Q

In which direction do action potentials travel within the MLF?

A

From the nucleus of CN VI to the nucleus of CN III.

The control centres activating these pathways will first activate the CN VI nucleus within the brain stem.

It is from a given CN VI nucleus that the action potential is taken up through the brainstem.

44
Q

What does damage to the MLF cause?

A

Inter-nuclear ophthalmoplegia (INOP)?

Involves loss of interneuron connectivity between CN VI and CN III.

45
Q

How would a patient with bilateral inter-nuclear ophthalmoplegia present?

A

Testing left lateral gaze: Left eye would rotate to the left but right eye would not.

Testing right lateral gaze: Right eye would look to the right but the left eye would not.

Both eyes would adduct because CN III is still functional and the pathway for convergence does not involve the MLF.

46
Q

Where does the pathway for convergence begin? Does it involve the MLF?

A

Does not involve MLF.

The cerebral cortex (the frontal eye field).

The neurons will drop down straight onto the nuclei of CN III.

Provides a direct innervation of CN III and therefore an innervation of the medial rectus muscles on both the left and right sides.

47
Q

Voluntary saccades are brought about by control centres in the ?.

A

cerebral cortex (e.g. frontal eye field)

48
Q

Outline the neuronal processes underlying left voluntary movement of the eyes.

A
  • Right frontal eye field becomes active.
  • Sends neurons down through the internal capsule and brainstem to synapse at the Parapontine reticular formation.

Right frontal eye field synapses with let PRF.

  • Will also activate the right CN III nucleus.

Frontal eye field can also dierectly innervate the CN III nuclei.

49
Q

What does the vestibulo-ocular reflex do?

A

Brings about a compensatory movement of the eyes in response to a movement of the head to keep the eyes fixed on target.

50
Q

When the head is rotating axially in a given direction (either left or right), the ? detect the movement and make both eyes look to the opposite (contralateral) side.

A

lateral semi-circular canals

51
Q

What does the dynamic part of the vestibular system do. What does it consist of?

A

Detects rotational movements of the head and brings about compensatory movement of the eyes.

Consists of three semi-circular canals arranged in mutually perpendicular axes.

52
Q

If the head is rotated axially, to the right, it is the ? lateral semi-circular canal that will be activated.

A

right

53
Q

The vestibibulo-ocular reflex can be tested with a comatose patient to test what?

A

Brainstem function.

54
Q

What is a Doll’s eye sign?

A

When the examiner observes a positive oculocephalic reflex, when the patient moves their eyes opposite to the rotation of their head, such that their eyes stay looking forward.

55
Q

Describe neuronal pathway underlying the vestibulo-ocular reflex.

A

Activation of the right lateral semi-circular canal will send action potentials along CN VIII on the right hand side to the right Vestibular nucleus.

This will then connect to the contralateral CN VI nucleus.

From this point, the left VI nucleus communicates with the contralateral CN III nucleus.

56
Q

The pathway for left and right conjugate gaze can be activated by both ? or ? control systems.

A

automatic, voluntary

57
Q

During excitation of one lateral gaze pathway, the ? will be inhibited.

A

antagonistic pathway

58
Q

At rest, the semi-circular canals have a ? and oppose each other equally. Excitation of a given lateral semi-circular canal will ? if the head is rotated towards it and ? if the head is rotated away from it.

A

tonic output, increase, decrease

59
Q

Damage to a given control system: do the eyes drift towards or away from the damged side? Why?

A

Towards.

Because normally, the output from the left and right sided control systems oppose each other equally.

Stronger side will push the eyes towards the weaker (damaged) side.

60
Q

If unilateral damage were to occur to a part of the Vestibulo-ocular reflex pathway in a conscious patient, what would you observe?

A

Jerk nystagus.

61
Q

What is a jerk nystagmus?

A

Repetitive involuntary eye movement with a fast and slow phase.

62
Q

Jerk nystagmus is described according to the direction of what?

A

The fast phase.

63
Q

Weakness of the left-sided eye movement control systems could be caused by what?

A

Vestibular neuritis, left-sided brainstem infarction involving left-sided vestibular nuclei (could be caused by a blockage of the PICA).

64
Q

Placing cold water into cone external auditory meatus mimics a ?.

A

lesion of the vestibular system or nucleus on that side

65
Q

What is the cold caloric test used to test?

A

It mimics lesion of the vestibular system or nucleus on that side. It tests brainstem functionality, vestibular system functionality and cortical functionality.

66
Q

How does the cold caloric test work?

A

Presence of cold water within the petrous part of the temporal bone will begin to change the temperature of fluid within part of the lateral semi-circular canal.

This will set up a convection current, causing it to move.

This movement of fluid within the lateral semi-circular canal mimics head rotation.

67
Q

In the cold caloric test, which way do the eyes move?

A

Normally, the eyes look slowly toward the affected cold water side.

This is followed by a fast correction (nystagmus) to the midline.

The nystagmus is away from the side with cold water.

68
Q

The warm caloric test uses warm water and the ? movement of the eyes should be seen to the cold caloric test.

A

opposite

69
Q

COWS can help you remember the direction of the jerk nystagmus seen:

A

Cold = Opposite

Warm = Same

70
Q

Outline the neuronal pupil reflex pathway.

A

The pupillary light reflex neural pathway on each side has an afferent limb and two efferent limbs. The afferent limb has nerve fibers running within the optic nerve (CN II). Each efferent limb has nerve fibers running along the oculomotor nerve (CN III).

The afferent limb carries sensory input. Anatomically, the afferent limb consists of the retina, the optic nerve, and the pretectal nucleus in the midbrain, at level of superior colliculus. Ganglion cells of the retina project fibers through the optic nerve to the ipsilateral pretectal nucleus.

The efferent limb is the pupillary motor output from the pretectal nucleus to the ciliary sphincter muscle of the iris. The pretectal nucleus projects crossed and uncrossed fibers to the ipsilateral and contralateral Edinger-Westphal nuclei, which are also located in the midbrain.

Each Edinger-Westphal nucleus gives rise to preganglionic parasympathetic fibers which exit with CN III and synapse with postganglionic parasympathetic neurons in the ciliary ganglion.

Postganglionic nerve fibers leave the ciliary ganglion to innervate the ciliary sphincter. Each afferent limb has two efferent limbs, one ipsilateral and one contralateral.

The ipsilateral efferent limb transmits nerve signals for direct light reflex of the ipsilateral pupil. The contralateral efferent limb causes consensual light reflex of the contralateral pupil.

71
Q

Explain what has happened if you:

  1. Shine light into left eye and left pupil doesn’t constrict but right does
  2. Shine light into right eye and left pupil doesn’t constrict but right does
A

Left shows no direct or consensual reflex to light so there may be unilateral damage to left EWN.

72
Q

What does lesion of the optic nerve result in?

A

No direct constriction, only consensual constriction.

73
Q

What could cause compression of CN III?

A

Aneurysm of posterior cerebral artery.

74
Q

Which muscle abducts the eye?

Which muscle depresses the eye?

A

Abducts - lateral rectus

Depresses - superior oblique

75
Q

How do LR, MR, SO, IO, SR and IR muscles act?

A
76
Q

Which muscles rotate around the red AND black axes?

A

Superior oblique and inferior oblique muscles.

Superior rectus and inferior rectus muscles.

77
Q

If only the superior oblique muscle were to contract, what direction would the eye move in?

A

Depressed and abducted.

78
Q

If only the inferior oblique muscle were to contract, what direction would the eye move in?

A

Elevated and abducted.

79
Q

Which three muscles abduct the eyeball?

A

Lateral rectus, superior oblique and inferior oblique.

80
Q

Which three muscles adduct the eyeball?

A

Medial rectus, superior rectus, inferior rectus.

81
Q

What are the 2 phases of jerk nystagmus?

A

Fast phase: the eyes move quickly back to the midline (rightwards) via the action of saccade centres in the cerebral cortex e.g. the frontal eye field.

Slow phase: the eyes slowly drift left - they are looking towards the damaged (pathological) left side.

82
Q

During the cold caloric test, what would you see in the case of:

Depressed cortical function

Unconscious with functional brainstem. Absent cortical function

Brainstem death

A

B3 CAI (13 decks)

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