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Neuroscience III > Oculomotor Mechanisms > Flashcards

Oculomotor Mechanisms Flashcards

1
Q

List some symptoms of oculomotor disturbances:

A
  1. blurred vision
  2. diploplia
  3. oscillopsia
  4. vertigo
  5. dysequilibrium/falls
  6. brainstem related symptoms (dysphagia or dystarthria, cerebellar signs, tinnitus or hearing loss)
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2
Q

The oculomotor nucleus is located in the:

A

rostral midbrain

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3
Q

The oculomotor nerve innervates ______ except these two:

A

all extraocular muscles

except lateral rectus and superior oblique

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4
Q

Describe the resting position with CN III lesion:

A

exotropia (lateral strabismus)
ptosis (drooping)
diploplia

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5
Q

Which motor components are impaired with CN III lesion?

A

no upward gaze

no medial gaze ipsilaterally

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6
Q

The pupillary light reflex tests which CN’s?

A

CN II and III

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7
Q

The pupillary light reflex tests integrate of connection between ___ and ___ via the ___.

A

retina and midbrain via the thalamus

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8
Q

Pupillary dilation and dec. pupillary light reflex is an important indicator of:

A

increased intracranial pressure

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9
Q

Describe the direct effect and consensual response to pupillary light reflex:

A

direct: shine light - pupil constricts
consensual: contralateral pupil also constricts

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10
Q

Describe the circuit for direct pupillary response:

A

(sensory) retina > optic nerve > optic tract >pretectum > CN III (motor)

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11
Q

Describe the circuit for consensual pupillary response:

A

fibers cross in pretectum to contralateral CN III

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12
Q

The trochlear nerve nucleus is located in:

A

caudal midbrain

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13
Q

Trochlear nerve innervates:

A

superior oblique muscle

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14
Q

Describe the resting position with CN IV lesion:

A

no apparent drift
maybe hypertropia (elevated) and extrusion
maybe diploplia

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15
Q

Which motor components are impaired with CN IV lesion?

A

no gaze down when adducted ipsilateral to lesion

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16
Q

How is CN IV tested?

A

pt. follows examiner’s finger medially and then downward (testing superior oblique muscle)

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17
Q

Abducens, CN VI, is located in:

A

caudal pons

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18
Q

Abducens, CN VI, innervates:

A

lateral rectus muscle

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19
Q

Describe the resting position with CN VI lesion:

A

esotropia (medial strabismus)

diploplia

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20
Q

Which motor components are impaired with CN VI lesion?

A

inability to gaze laterally on ipsilateral side of lesion

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21
Q

Define conjugate eye mvmnt:

A

both eyes look same way (i.e.: both to R/L/up/down)

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22
Q

Define horizontal conjugate gaze:

A

Coordination that requires one eye to adduct while the other abducts

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23
Q

The fiber bundle medial to abducens nucleus bilaterally is:

A

medial longitudinal fasciculus (MLF)

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24
Q

The medial longitudinal fasciculus carries fivers that interconnect with:

A

CN VI
contralateral CN III nuclei
vestibular nuclei

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25
Q

With damage to adbucens nucleus, resting position is ______; the mvmnt deficit is:

A

rests in medial strabismus

lateral gaze paralysis (no lateral gaze from either eye toward the side of lesion)

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26
Q

Fibers in the MLF are axons of internuclear neurons of ____ nerve that project to and excite:

A

abducens

excite contralateral oculomotor motor neurons

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27
Q

Internuclear opthalmoplegia (INO) is a lesion of:

A

just the MLF between CN III and IV

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28
Q

With INO, the position at rest is _____; the mvmnt deficit is:

A

no drift

no ipsilateral eye adduction with lateral gaze to contralateral side of lesion

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29
Q

What is vertical conjugate gaze? What nerve and muscles produce the movement?

A

upward/downward/torsional gazes

produces by CN III nucleus innervating superior/inferior rectus bilaterally

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30
Q

Keeping an image centered on the fovea requires:

A

fxnal LMN’s of CN III, IV, IV plus CNS mechanisms

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31
Q

Impairments of gaze fixation in the primary position (straight ahead) may be:

A

resting nystagmus
saccadic intorsions
ocular flutter

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32
Q

What is gaze fixation?

A

ability to hold eyes in fixed position to maintain steady visual target on fovea

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33
Q

Which areas are involved in regulating gaze fixation?

A

cortex and brainstem (vestibular, cerebellum)

34
Q

At the end of eye movement, gaze must be fixated on target. This process is called:

A

step command

from “neural integrator”

35
Q

The neural integrator for horizontal eye mvmnts:

A

medial vestibular nucleus and nucleus prepositus hypoglossi in MEDULLA

36
Q

The neural integrator for vertical eye mvmnts:

A

interstitial nucleus of Cajal in MIDBRAIN

37
Q

Vest-Cb (flocculus) takes into account these qualities of eye mvmnts:
In order to:

A

velocity and amplitude of eye mvmnts from cortex and through neural integrator, then generates gaze fixation at new, eccentric eye position

38
Q

VOR fxn:

A

maintain visual target on fovea while head is moving through smooth high velocity eye mvmnts in equal/opposite directions to head motion

39
Q

VOR mechanism speed and latency:

A

generates eye mvmnt up to 400 degrees/second; shortest latency reflex in body at ~10ms latency

40
Q

VOR involves receptors in the:

A

inner ear, vesitubular nuclei, and connections to eye mvmnt nuclei through MLF

41
Q

What region coordinates amplitude and adaptation of VOR?

A

Vest-Cb

42
Q

Describe optokinetic nystagmus:

A

a “normal” nystagmus that allows for stabilization of a series of moving visual targets on the fovea (i.e.: watching telephone poles go by); requires both slow and fast rhythmical eye mvmnts

43
Q

What structures allow for fxn of optokinetic nystagmus?

A

cortical mechanisms initiate

brainstem smooth pursuit mechanisms are important

44
Q

Slow rhythmical eye mvmnt for tracking or maintaining moving visual target on fovea is called:

A

smooth pursuit

45
Q

Fast rhythmical eye mvmnt for repositioning is called:

A

saccade (can be voluntary or reflexive)

46
Q

Saccades are recruited when moving from one visual target to another or if target velocity is > ___.

A

60 degrees/sec

47
Q

Saccades are quick jerks with velocities of:

A

250-600 degrees/sec

48
Q

Describe the 2 components to saccades:

A
  1. PULSE SIGNAL: to move eye to new position

2. STEP COMMAND: to hold eye in new position (gaze fixation mechs via neural integrator)

49
Q

Describe the mechanism for horizontal saccades:

A
  1. initiated by cortical area 8/frontal eye field
  2. contra. paramedian pontine RF of pons
  3. ipsi CN III, CN VI nucleus, MLF
  4. once eyes reach target, step command generated via neural integrator
50
Q

Damage to frontal eye field results in:

A

inability to initiate saccages to contra. side; gaze preference is towards same side of cortical lesion

51
Q

Damage to pons results in:

A

inability to generate saccades to ipsi. side; gaze preference is away from side of lesion

52
Q

In order for vertical saccades to be affected, what must occur?

A

bilateral damage

53
Q

Describe the mechanism for vertical saccades:

A
  1. frontal eye field
  2. midbrain
  3. interstitial nucleus of canal
  4. B CN III and IV nuclei
54
Q

What is the alternate pathway for voluntary saccades?

A

basal ganglia to superior colliculus

55
Q

What structure regulates the amplitude of saccades?

A

cerebellar vermis

56
Q

Reflexive saccades (orienting behavior) involve ____ projecting to the:

A

subcortical projection to the superior colliculus

57
Q

Do reflexive saccades require involvement of the cortex?

A

NO! the retina are directly to superior colliculus

58
Q

Words used to document the quality of impaired saccades include:

A

slow
hypermetric
hypometric

59
Q

When is smooth pursuit used?

A

when head is still and target velocities < 60 degrees/sec

60
Q

Information on velocity and trajectory of target in smooth pursuit are registered through:

A

visual system

Cerebral cortex: frontal eye field, parietal, temporal and occipital visual association areas

61
Q

Information on velocity and trajectory of target in smooth pursuit are registered through visual system then projected to:

A

Cb (vermis and flocculus) and medial vestibular nucleus

62
Q

Smooth pursuit eye mvmnts are generated via:

A
  1. medial vestibular
  2. abducens nuclues
  3. MLF for conjugate gaze
63
Q

Abnormal smooth pursuit may include:

A

corrective saccades

64
Q

impaired smooth pursuit is a sign of:

A

pathology of CNS

but difficult to locate the lesion without other signs

65
Q

Describe vergence:

A

aka accommodation

parasympathetic reflex involving near focus and pupillary constriction

66
Q

Describe the pathway in vergence:

A
  1. visual assoc. cortex
  2. midbrain (pretectum)
  3. B oculomotor nuclei
67
Q

Nystagmus is named by the direction of:

A

fast (saccadic) component

68
Q

How many different kinds of nystagmus exist?

A

60; useful in diagnosing certain disorders

69
Q

Nystagmus is a symptom in these types of disorders:

A

vestibular disorders
cerebellar disorders
other brainstem lesions

70
Q

T or F: Some types of nystagmus are normal

A

True

71
Q

4 types of Physiologic (normal) Nystagmus

A
  1. optokinetic (voluntary eye mvmnts)
  2. rotational induced
  3. Caloric induced (COWS)
  4. end range
72
Q

When do you see rotational-induced nystagmus?

A

When they’ve been passively spun around. Fast phase is in direction of spin.

73
Q

Caloric Induced (COWS)

A

Caloric testing (H2O in ear canals) artificially induces flow of endolymph in semicircular canals, causing nystagmus.

74
Q

What eye ROM can cause end-range nystagmus?

A

> 30 degrees

75
Q

Pathological Nystagmus types

A
  1. Spontaneous
  2. Gaze-evoked
  3. Congenital
  4. Positional
76
Q

When do you see spontaneous nystagmus?

A

At rest. ALWAYS CNS pathology.

77
Q

What must you differentiate Gaze-evoked nystagmus from?

A

normal end range nytagmus

78
Q

What brings on Positional Nystagmus?

A

Change in head position. Seen in BPPV

79
Q

Which nystagmuses are always signs of Central pathology?

A

Vertical, pure torsional, and direction changing nystagmus

80
Q

Which nystagmuses will diminish over time?

A

Peripheral nystagmus, because of central compensating mechaisms.

Neuroscience III (7 decks)

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