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!!!!! BRS YR2 !!!!! > Neuro - Visual system pt. 3 + 4 > Flashcards

Neuro - Visual system pt. 3 + 4 Flashcards

1
Q

Where does the visual pathway start and end?

A

transmits signal form eye to visual cortex

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2
Q

What landmarks does the visual pathway go through?

A

eye → through optic nerve → optic chiasm → optic tract → lateral geniculate nucleus → optic radiation → primary visual cortex

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3
Q

What is the optic nerve?

A

ganglion nerve fibres

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4
Q

What is the optic chiasm?

A

half of the nerve fibres cross here (53% of fibres)

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5
Q

What is the optic tract?

A

ganglion nerve fibres exit the optic chiasm as the optic tract

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6
Q

What is the lateral geniculate nucleus?

A

→ located in thalamus

→ where the ganglion nerve fibres synapse

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7
Q

What is the optic radiation?

A

→ 4th order neurone

→ travel in pairs, taking information from homonymous quadrants of vision

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8
Q

What is the primary visual cortex or striate cortes?

A

→ centre within the occipital lobe
→ processes visual information
→ Extra-Striate Cortex for further higher visual processing

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9
Q

What are the different neurones that make up the visual pathway from the retina to the lateral geniculate nucleus?

A

→ 1st order neurones
→ 2nd order neurones
→ 3rd order neurones

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10
Q

What are the 1st order neurones?

A

rod + cone retinal photoreceptors

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11
Q

What are the 2nd order neurones?

A

retinal bipolar cells

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12
Q

What are the 3rd order neurones?

A

→ Optic Nerve
→ Partial Decussation at Optic Chiasma – 53% of ganglion fibres cross the midline
→ Optic Tract
→ Destination = Lateral Geniculate Nucleus (LGN) in Thalamus

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13
Q

What do lesions anterior to the optic chiasma affect?

A

visual field in one eye only

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14
Q

What do lesions posterior to the optic chiasma affect?

A

visual field in both eyes

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15
Q

Where do crossed fibres at the optic chiasma originate form?

A

→ predominantly originate from the nasal retina

→ responsible for the temporal half of the visual field in each eye

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16
Q

Where do uncrossed fibres at the optic chiasma originate form?

A

→ predominantly originate from the temporal retina

→ responsible for the nasal half of the visual field in each eye

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17
Q

What visual defect would a left optic nerve compression cause?

A

unilateral field loss in left eye

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18
Q

What visual defect would a optic chasmal compression from a pituitary tumour cause?

A

bitemporal hemianopia

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19
Q

What visual defect would a left cerebrovascular event or stroke cause?

A

homonymous hemianopia (contralateral to lesion)

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20
Q

What is quadrant-anopia?

A

→ loss in one of the quadrants of vision

→ usually homonymous

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21
Q

What can cause quadrant-anopia?

A

lesions to the optic radiations in the temporal or parietal lobes

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22
Q

What is macular sparing?

A

homonymous hemianopia with a small inner circle of clear vision (sparing of the macula of central vision)

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23
Q

What can cause macular sparing?

A

→ lesions to optic radiation in the occipital lobe?
→ stroke
→ damage to the primary visual cortex

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24
Q

What can typically cause a bitemporal hemianopia?

A

enlargement of the pituitary gland due to a tumour

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25
Q

What can typically cause a homonymous hemianopia?

A

stroke or cerebrovascular event

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26
Q

Why is the macula spared sometimes with homonymous hemianopia?

A

→ area representing the macula is well protected

→ receives dual blood supply from both right + left posterior cerebral arteries

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27
Q

What is the main pupillary function?

A

regulates light input to the eye

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28
Q

What does the pupil do in light?

A

→ pupillary constriction
→ decreases spherical aberrations and glare
→ increases depth of field
→ reduces bleaching of photo-pigments
→ mediated by parasymapthetic nerve (within CN III)
→ causes circular muscle to contract

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29
Q

What does the pupil do in the dark?

A

→ pupillary dilation
→ increase slight sensitivity in the dark by allowing more light into the eye
→ mediated by the sympathetic nerve
→ causes radial muscles to contract

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30
Q

What cells participate in the pupillary reflex pathway?

A

small sub-section of retinal ganglion cells

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31
Q

How do cells form the afferent pathway of the pupillary reflex?

A

→ Rod and Cone Photoreceptors synapsing on Bipolar Cells synapsing on Retinal Ganglion Cells
→ Pupil-specific ganglion cells at posterior third of optic tract before entering the Lateral Geniculate Nucleus
→ Afferent (incoming) pathway from each eye synapses on Edinger-Westphal Nuclei on both sides in the dorsal side of the brainstem

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32
Q

How do cells form the efferent pathway of the pupillary reflex?

A

→ Edinger-Westphal Nucleus → Oculomotor Nerve Efferent → Synapses at Ciliary ganglion → Short Posterior Ciliary Nerve → Pupillary Sphincter of the iris

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33
Q

Why do both eyes respond to the pupillary reflex?

A

only one eye needs to be stimulated, as the afferent pathway in just one eye can stimulate the efferent pathway in both eyes

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34
Q

What is a direct light reflex?

A

constriction of the pupil of the light-stimulated eye

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35
Q

What is the consensual light reflex?

A

constriction of the pupil of the other eye (that hasn’t been stimulated)

36
Q

What could cause damage to the afferent pathways of the pupillary reflex?

A

damage to the optic nerve

37
Q

What would be the effect of a right afferent pathway defect?

A

→ right eye light stim = no pupil constriction in both eyes

→ left eye light stim = normal pupil constriction in both eyes

38
Q

What could cause damage to the efferent pathways of the pupillary reflex?

A

damage to the 3rd nerve

39
Q

What would be the effect of a right efferent pathway defect?

A

any eye light stim = only left pupil constriction, no right pupil constriction

40
Q

What is the swinging torch test?

A

→ best way to detect RAPD (relative afferent pupillary defect)
→ elicited by swinging torch from left eye to right eye
→ the side which doesn’t cause pupil constriction = where the defect is

41
Q

How is eye movement facilitated?

A

→ by 6 extra ocular muscles

→ innervated by 3 cranial nerves (III, IV, VI)

42
Q

What is duction?

A

eye movement of one eye

43
Q

What is version?

A

simultaneous movement of both eyes in the same direction

44
Q

What is vergence?

A

simultaneous movement of both eyes in opposite directions

45
Q

What is dextroversion?

A

looking to the right with both eyes

46
Q

What is levoversion?

A

looking to the left with both eyes

47
Q

What is convergence?

A

simultaneous adduction (inward) movement in both eyes when viewing a near object

48
Q

What is saccade?

A

→ short fast burst of eye movement

→ up to 900 degrees a second

49
Q

What are the different types of saccade?

A

→ reflexive saccade to external stimuli
→ scanning saccade
→ predictive saccade to track objects
→ memory-guided saccade

50
Q

What is smooth pursuit?

A

→ sustained slow movement
→ up to 60 degrees per second
→ driven by motion of a moving target across the retina

51
Q

What are the 6 extra-ocular muscles?

A 
Superior rectus
Inferior rectus
Lateral rectus
Medial rectus
Inferior Oblique
Superior Oblique
52
Q

What are the main purposes of the extra-ocular muscles?

A

→ attach eyeball to orbit

→ straight + rotatory movement

53
Q

What are the 4 straight extra-ocular muscles?

A

Superior rectus
Inferior rectus
Lateral rectus
Medial rectus

54
Q

Which muscles come out from a cone from the back of the orbit? Which ones don’t?

A

→ all of them come out from the back, except Inferior Oblique
→ inferior oblique comes in nasally

55
Q

What is the purpose of the superior rectus muscle?

A

→ Attached to the eye at 12 o’clock

→ Moves the eye up

56
Q

What is the purpose of the inferior rectus muscle?

A

→ attached to the eye at 6 o’clock

→ moves the eye down

57
Q

What is the purpose of the lateral rectus muscle?

A

→ Also called external rectus
→ Attaches on the temporal side of the eye
→ Moves the eye toward the outside of the head (toward the temple)

58
Q

What is the purpose of the medial rectus muscle?

A

→ Also called internal rectus
→ Attached on the nasal side of the eye
→ Moves the eye toward the middle of the head (toward the nose)

59
Q

What is the purpose of the superior oblique muscle?

A

→ Attached high on the temporal side of the eye
→ Passes under the Superior Rectus
→ Moves the eye in a diagonal pattern down and out
→ Travels through the trochlea

60
Q

What is the purpose of the inferior oblique muscle?

A

→ Attached low on the nasal side of the eye
→ Passes over Inferior Rectus
→ Moves the eye in a diagonal pattern - up and out

61
Q

What extra-ocular muscles does the Superior branch of CN III (oculomotor) innervate?

A

→ superior rectus

→ levator palpebrae superioris

62
Q

What does the levator palpebrae superioris do?

A

raises the eyelid

63
Q

What extra-ocular muscles does the inferior branch of CN III (oculomotor) innervate?

A

→ inferior rectus
→ medial rectus
→ inferior oblique

64
Q

What extra-ocular muscles does CN IV (trochlear) innervate?

A

superior oblique

65
Q

What extra-ocular muscles does CN VI (abducens) innervate?

A

lateral rectus

66
Q

What muscle controls abduction of the eye?

A

lateral rectus

67
Q

What muscle controls adduction of the eye?

A

medial rectus

68
Q

What muscle elevates + abducts the eye?

A

superior rectus

69
Q

What muscle depresses + abducts the eye?

A

inferior rectus

70
Q

What muscle elevates + adducts the eye?

A

inferior oblique

71
Q

What muscle depresses + adducts the eye?

A

superior oblique

72
Q

What eye movement does supraduction test?

A

elevation of one eye

73
Q

What eye movement does supra version test?

A

elevation of both eyes

74
Q

What eye movement does infraduction test?

A

depression of one eye

75
Q

What eye movement does infraversion test?

A

depression of both eyes

76
Q

What eye movement does right dextroversion test?

A

right abduction + left adduction

77
Q

What eye movement does left dextroversion test?

A

right adduction + left abduction

78
Q

What is torsion?

A

rotation of eye around he anterior-posterior axis of the eye

79
Q

What is third nerve palsy?

A

→ weakness of the third cranial nerve

→ muscle innervated by third nerve don’t work properly

80
Q

What are the features of third nerve palsy?

A

→ Affected eye down and out
→ Droopy eyelid (loss of elevator palpebrae superioris)
→ Unopposed superior oblique innervated by fourth nerve (down)
→ Unopposed lateral rectus action innervated by sixth nerve (out)

81
Q

What is sixth nerve palsy? What are the features?

A

→ Affected eye unable to abduct and deviates inwards

→ Double vision worsen on gazing to the side of the affected eye

82
Q

What is Nystagmus?

A

oscillatory eye movement

83
Q

What is Optokinetic Nystagmus?

A

smooth pursuit + fast phase reset saccade

84
Q

What is optokinetic nystagmus reflex?

A

useful in testing visual acuity in pre-verbal children by observing the presence of nystagmus movement in response to moving grating patterns of various spatial frequencies

85
Q

What does presence of the Optokinetic Nystagmus reflex signify?

A

signifies that the subject has sufficient visual acuity to perceive the grating pattern

!!!!! BRS YR2 !!!!! (72 decks)

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