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Neuroscience1 > Oculomotor System > Flashcards

Oculomotor System Flashcards

1
Q

General function of the oculomotor system

A
  1. Bring targets on the fovea

2. Keep them there

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2
Q

Movement systems that stabilize eye when head moves

A
  1. Vestibulo-ocular

2. Optokinetic

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3
Q

Vestibulo-ocular movement system function

A

Gaze stabilization- Vestibular input holds image stable on retina during head and body movement

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4
Q

Optokinetic movement system function

A

Visual input holds images stable on retina during sustained or slow head rotation

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5
Q

Movement systems that keep the fovea on a visual target

A
  1. Saccade
  2. Smooth pursuit
  3. Vergence
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6
Q

Saccade General function

A

Brings new objects of interest into the fovea

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7
Q

Smooth pursuit General function

A

Holds image of moving target on the fovea

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8
Q

Vergence

A

Adjusts eyes for viewing different distances in depth

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9
Q

Systems that allow for conjugate eye movement

A

Vestibulo-ocular
Optokinetic
Saccade
Smooth Pursuit

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10
Q

Systems that allow for disconjugate movements

A

Allows for convergence or divergence

Vergence movement system

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11
Q

Saccade System

A

Used to quickly reposition the eyes (fovea) to focus on an image that has suddenly been moved from the fovea, has vertical and horizontal pathways

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12
Q

Saccade

A

Rapid conjugate eye movement required to bring the image back into focus on the fovea, response to visual, auditory, memory of locations, verbal commands

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13
Q

Conjugate system location

A

Horizontal gaze center is located in pontine reticular formation, paramedian pontine reticular formation (PPRF), adjacent to the abducens nucleus

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14
Q

UMN control of conjugate system

A

Interneurons in the frontal eye fields (area 8) and superior Colliculus

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15
Q

We _____ objects in the periphery and _____ objects only when they are focused in the fovea

A

Detect, see

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16
Q

Rotatory nystagmus

A

Rapid Saccade movement during turning of head where visual input is momentarily impaired until the foveas fixate on the next point

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17
Q

How does vestibulo-ocular reflex work?

A

Flow of endolymph is opposite to direction of head turning until it catches up and stabilizes

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18
Q

Optokinetic reflex

A

Following and resetting of focal point
-postrotatory nystagmus- slow eye movement in the direction of prior rotation and the Saccade in the opposite direction of prior rotation

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19
Q

UMN control of smooth pursuit

A

PPRF, PVC of caudal temporal gyrus and superior colliculus

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20
Q

PPRF- Voluntary and reflex pathways in smooth pursuit

A

Voluntary- saccades initiated from frontal eye fields

Reflex- vestibulo-ocular reflex

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21
Q

Conjugate eye movement in smooth pursuit is influenced by ___________ to the _________ and then ______/_______

A

Cerebellum, vestibular nuclei, vertical/horizontal gaze centers

22
Q

Vergence system is controlled through

A

Reticular formation at midbrain level

23
Q

Function of disconjugate movements

A

Necessary for the foveation of an image as it moves towards/away from you

24
Q

Convergence steps

A
  1. Activation of both medial rectus muscles, overriding lateral
  2. Eyes come together
  3. Pupillary constriction and accommodation to overcome blurring
25
Q

Deficits in the horizontal or vertical gaze centers do not effect

A

Convergence or accommodation

26
Q

Superior Colliculus nucleus location

A

Nucleus located rostrally in the midbrain tectum

27
Q

Superior Colliculus receives UMN fibers from

A

Ipsilateral: frontal eye fields, brodmann’s area 8, occipital lobe and caudal temporal lobe, tectobulbar connections to CN for voluntary/involuntary movements of the eye

28
Q

Superior Colliculus retinal projections

A

From optic tract via brachium of the superior Colliculus

29
Q

Tectospinal tract- location/function

A

Crosses midbrain and descends to cervical spinal cord levels

-reflex turning of head and neck in response to visual/auditory cues

30
Q

All CN involved with voluntary/involuntary movement of eye are interconnected through ____________

A

Medial longitudinal fasciculus

31
Q

Abducens nerve (CN VI) LMN

A
  1. Starts in R frontal eye field
  2. Tectobulbar fibers synapse in contralateral PPRF
  3. Synapse in contralateral abducens nucleus
  4. Innervate lateral rectus muscle, abduction of eyeball
32
Q

CN VI- horizontal conjugate gaze

A
  1. Starts in frontal eye field of brain
  2. Synapses in contralateral PPRF
  3. Synapses in contralateral abducens nucleus
  4. Interneuorns in abducens project to ipsilateral and contralateral oculomotor nucleus
  5. Ipsilateral oculomotor nucleus inhibits ipsilateral medial rectus
    Contralateral nucleus innervates contralateral medial rectus
33
Q

Strabismus

A

A visible turn of one eye that may be constant

Also termed tropia, esotropia, exotropia

34
Q

Phoria

A

The point of vergence of the eyes

35
Q

Esophoria

A

Where the eyes are postured in front of the point of focus

36
Q

Exophoria

A

Eyes are postured in back of the point of focus

37
Q

Esotropia

A

Lesion of the abducens nerve fibers

result in unopposed adduction of the ipsilateral eye

38
Q

Lesion of abducens nucleus (including PPRF)

A

Paralysis of ipsilateral horizontal gaze

39
Q

Internuclear Ophthalmoplegia- where is it?

A

MLF damaged in the pons

40
Q

Internuclear Ophthalmoplegia symptoms

A
  • action of abducens and oculomotor are uncoupled
  • full excursion of (contralateral) abducting eye
  • impaired adduction of (ipsilateral) eye
  • pendular nystagmus in abducting eye
41
Q

Pendular nystagmus

A

In abducting eye during internuclear Ophthalmoplegia

-loss of inhibitory fibers in MLF

42
Q

Trochlear nerve CN IV LMN

A
  1. Start in Trochlear nucleus
  2. Loop behind periaqueductal grey and decussate
  3. Courses around brainstem lateral to oculomotor and between the superior/posterior cerebral arteries
  4. Innervates the superior oblique
43
Q

Function of Trochlear nerve

A

Superior oblique- rotation and depression of eyeball

44
Q

Lesion of CN IV

A

Inability to look down (vertical gaze), problems walking down stairs

45
Q

Vertical gaze center location

A

Interstitial nucleus of Cajal, located near Trochlear nucleus

46
Q

Oculomotor Nerve CN III- LMN

A
  1. Start in oculomotor nucleus
  2. Innervate ipsilateral superior oblique, medial rectus, inferior oblique, inferior rectus
    Innervate contralateral superior rectus
47
Q

CN III preganglionic parasympathetic fibers

A
  1. Start in Edinger-Westphal nucleus
  2. Transverses tegmentum near red nucleus, cross cerebral peduncles
  3. Exit in the interpeducular fossa between the superior and posterior cerebral arteries
  4. Innervate the ciliary ganglia
48
Q

Exotropia

A

Lesion of oculomotor nerve

49
Q

Lesion of CN III symptoms

A
  • Oculomotor palsy- paralysis of all extraocular eye muscles except LR SO, results in unopposed abduction of ipsilateral eye
  • Drooping eyelid due to levator palpebrae superioris
  • Loss of ciliary ganglia- dilation of pupil
50
Q

Argyle-Robertson Pupil

A

Pupil is small in dim light and non reactive to light

-will constrict in accommodation associated with convergence

51
Q

Horner’s syndrome- what is it?

A

Lesion of sympathetic pathway, descending influence from hypothalamus directed to preganglionic sympathetic neurons in spinal cord

52
Q

Horner’s syndrome- clinical signs

A

Ptosis- loss of levator palpebrae superioris
miosis (pupil constricted)- loss of dilator control- unopposed constrictor tone (parasympathetic)
Dry skin- loss of sympathetic control of sweat glands
Flushed skin- lack of constriction of capillary fields

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