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Neuroscience > N20: Visual system > Flashcards

N20: Visual system Flashcards

1
Q

what are the 3 layers of the eye?

A
  • corneoscleral coat
  • choroid coat
  • retina
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2
Q

Describe the corneoscleral coat.

A
  • tough connective tissue
  • sclera white (hole for optic nerve)
  • cornea transparent (refraction of light is zero)
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3
Q

Describe the choroid coat.

A
  • highly vascular
  • choroid: absorbs light – prevents reflection
  • ciliary body: produces aqueous humor
  • iris – regulates light entering the eye
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4
Q

Describe the retina.

A

contains photoreceptors - rods and cones

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5
Q

what permits accommodation for near vision?

A

biconvex lens which is elastic to allow it to change its shape

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6
Q

what are the anterior and posterior chambers filled with?

A

aqueous humor

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7
Q

what lies posterior to the lens?

A

larger vitreal cavity filled with vitrious humor (also called the vitreous body), which is avascular and gelatinous

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8
Q

what anchors the lens in place?

A

lens is suspended from ciliary body

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9
Q

what is the opening inn sclera through which the optic nerve passes?

A

lamina cribrosa

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10
Q

what causes a glaucoma?

A

distribution of balance of flow of aqueous humour from posterior to anterior chamber so pressure is exterted on the retina

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11
Q

what secretes aqueous humor?

A

cilliary body

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12
Q

what adjust the lens?

A

cilliary muscles

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13
Q

what stops stray light entering pupil?

A

melanocytes at the back of iris

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14
Q

what is the difference in melanin in blue and brown eyes?

A

blue eyes- low melanin

brown eyes- high melanin

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15
Q

what part of the eye allows us to read?

A

fovea centralis

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16
Q

what area of the eye is the blind spot?

A

optic disk (where optic nerve exits)

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17
Q

what happens to an image projected in retina?

A

turned upside down and back to front

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18
Q

what is higher in number in the retina?

A

much more rods than cones

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19
Q

what does each rod contain?

A

rhodopsin- a light sensitive pigment

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20
Q

what does each cone conatin?

A

one of 3 opsin pigments, sensitive to either red, green or blue light

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21
Q

what effect does light have on rods and cones?

A

hyperpolarizes them, decreasing their firing rate

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22
Q

where is information passed to in the retina?

A

Information passes from photoreceptor to bipolar cell to retinal ganglion cell

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23
Q

what modifies the information passing from photoreceptors to bipolar cell to retinal ganglion cell?

A

association neurons

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24
Q

what Is the point of fixation?

A

Detailed high resolution colour vision at the Fovea centralis

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25
Q

what are the reasons for the f fovea centralis’s high visual acuity?

A

(1) Thinning of retinal layers
(2) Lack of rods, high concentrations of cones
(3) Low convergence

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26
Q

when are axons of the otic nerve myelinated?

A

Axons are not myelinated within the eye, but are myelinated after passing the lamina cribrosa

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27
Q

what produces myelin in the optic nerve?

A

oligodendrocytes

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28
Q

what is the optic nerve surrounded by?

A

meninges

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29
Q

what causes the blind spot at the optic disc?

A

lack of rods and cones

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30
Q

where is visual information going to in the thalamus?

A

lateral geniculate nucleus

31
Q

what are the basic elements of visual pathway?

A
  • optic nerve
  • optic chiasma
  • optic tract
  • Lateral geniculate nucleus (thalamus)
  • optic radiation
  • striate cortex (primary visual cortex)
32
Q

what is the optic chiasma?

A

crossing point for fibres coming out of the eye

33
Q

which of the fibres cross at the chiasma?

A

nasal retina fibres

34
Q

which fibres stays on the ipsilateral side?

A

temporal retina fibres

35
Q

what vision laterally crosses at the chiasma?

A

peripheral vision

36
Q

what does each optic tract contain?

A

opposite visual world derived from both eyes

37
Q

what causes objects to be projected onto the retina reversed and upside down?

A

lens

38
Q

what does each optic tract, lateral geniculate nucleus (of the thalamus), optic radiation and visual cortex deal with?

A

visual information from the contralateral field

39
Q

In addition to the projection to the primary visual cortex, where else do fibres from the retina project to?

A
  • The pretectal area and nearby superior colliculus (probably functions in sustained pupillary contraction in bright light).
  • A small number of fibres leave the dorsal surface of the optic chiasma and enter the suprachiasmatic nucleus of the hypothalamus (probably involved in circadian rhythm, particularly diurnal hormonal changes and sleep)
40
Q

what does the superior colliculus function in?

A

saccadic eye movements

41
Q

what does superior colliculi receive input from?

A

visual cortex, frontal eye fields and spinal cord

42
Q

where does superior colliculi give output to?

A

Nuclei of CN III, IV and VI, motor nucleus of VII, and spinal cord

43
Q

how does fibres from the lateral geniculate nucleus of the thalamus reach the primary visual cortex?

A

geniculocalcarine tracts (also called the optic radiation)

44
Q

what do fibres from the lateral geniculate nucleus to the primary cortex initially form?

A

part of the internal capsule

45
Q

what path do the fibres carrying visual information from the upper half of the visual field?

A

fibres first loop anteriorly around the temporal part of the lateral ventricle in meyer’s loop ending below the calcarine sulcus

46
Q

where is the visual cortex found?

A

Surrounds the calcarine sulcus in the occipital cortex, it is thinner than most cerebral cortex

47
Q

what is the visual cortex referred to as?

A

area 17 of Brodmann

48
Q

why is the primary cortex also called the striate cortex?

A

prominent stripe of myelinated fibres found in layer IV which can be seen with the naked eye, called the line of Gennari.

49
Q

where is the lower visual field projected to?

A

gyrus superior to calcarine sulcus

50
Q

where does the macula project to?

A

posterior pole of the visual cortex and occupies a much greater proportion of the cortex relative to the size of the visual field it covers

51
Q

where do objects in the centre visual field go on the visual cortex?

A

back of the visual cortex/occipital lobe

52
Q

where do periphery vision go on the visual cortex?

A

further forward in the visual cortex/occipital lobe

53
Q

where is colour, orientation and faces processed in the visual association cortex?

A

colour -area 18
orientation- area 19
faces- area 20

54
Q

what is the main blood supply to primary visual cortex?

A

posterior cerebral

55
Q

where do posterior and middle cerebral arteries overlap?

A

occipital pole-macular sparing

56
Q

what happens in both pupils when light is shone into right eye?

A
  • Right pupil constricts- direct light reflex

- Left pupil constricts - consensual reflex

57
Q

what is required for the accommodation reflex?

A

requires input to oculomotor nucleus from the visual cortex?

58
Q

what does the accomodation reflex produce?

A
  • lens thickening (ciliary muscle)
  • pupillary constriction (increase field depth)
  • convergence of eyes (medial recti)
59
Q

when is accommodation reflex used?

A

change in point of focus i.e from close to far away

60
Q

what is the definition of hemianopia?

A

Blindness for half the field of vision in one or both eyes

61
Q

what is it called when vision is lost in the same visual field in both eyes?

A

homonymous

62
Q

what is it called when vision is lost in different visual field of each eye?

A

heteronymous

63
Q

What would be the effect of a lesion of Meyer’s Loop on the right side?

A

lose one quadrant of vision

64
Q

what provides the movement s in response to visual stimuli i.e tracking moving objects?

A

visual cortex

65
Q

what provides movements of command (movements that are independent of moving visual stimuli) ?

A

frontal eye fields

66
Q

what is tracking movements known as?

A

smooth pursuit eye movements

67
Q

what is movements of command known as?

A

saccadic eye movements

68
Q

Describe the effects of myopia.

A
  • short-sighted
  • able to focus near objects
  • unable to focus distant objects
  • eye ball relatively too long
69
Q

what is the treatment of myopia?

A

treatment concave lens to diverge light

70
Q

Describe the effects of hyperopia.

A
  • long-sighted
  • unable to focus near objects
  • able to focus distant objects
  • eye ball relatively too short
71
Q

what is the treatment of hyperopia?

A

treatment convex lens to converge light

72
Q

Describe the effects of presbyopia.

A

-normal age change
-gradual loss of accommodation
-lens less elastic
-ciliary muscles weaker
-Near point:
100 mm in young adults
800 mm in old age

73
Q

what is the treatment of presbyopia?

A

treatment convex lens to converge light

Neuroscience (21 decks)

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