5 –The visual system Flashcards

1
Q

How many pairs of cranial Nerve do we have?

A

12 pairs

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2
Q

What makes cranial nerves 1 and 2 different?

A

They develop from the CNS

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3
Q

What is cranial nerve 1 an extension of?

A

Our telencephalon

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4
Q

What is cranial nerve 2 an extension of?

A

Our diencephalon

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5
Q

Describe the cornea

A

The clear outer portion of the eye

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6
Q

What is the role of the cornea?

A

It filters light first

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7
Q

Describe the sclera

A

It is a continuation of the cornea

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8
Q

What part of the eye does the sclera form?

A

It is responsible for the white part of your eye

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9
Q

What are the responsibilities of the sclera and cornea?

A

They both protect the eye

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10
Q

What is the role of the sclera

A

It is the attachment point of all the muscles to be able to move the eye

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11
Q

Name the structures that form the outer layer fo the eye

A

The cornea and sclera

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12
Q

What is the middle layer of the eye composed of?

A
  1. The choroid
  2. the iris
  3. Ciliary body
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13
Q

Describe the choroid

A

It is very vascular

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14
Q

Why is the choroid very vascular

A

It supplies both the cornea and the retina

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15
Q

What is the iris and what us it responsible for?

A

It is a pigmented layer responsible for our eye color and it controls the amount of light entering the eye

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16
Q

What is the Iris composed of?

A

Different muscles the are in a circular shape

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17
Q

What do the muscles surrounding the iris do?

A

They can either contract or dilute to change the diameter of the pupil

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18
Q

What is the pupil?

A

The central opening of the iris

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19
Q

What does the Ciliary body attach via?

A

Attaches via the suspensory ligament to the lens

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20
Q

What does the Ciliary body do?

A

By pulling on the suspensory ligaments it can stretch and change the shape of the lens
This ultimately control the amount of light reaching the retina

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21
Q

What is the inner most layer?

A

The retina

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22
Q

What is the retina full of?

A

Neurones that receive light

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23
Q

What is found on the visual axis of the retina?

A

The macula

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24
Q

Describe the macula

A

It Is an area where there is a high density of cones only

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25
Q

What is the centre of the macula called?

A

The fovea

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26
Q

What is special about the fovea?

A

It is the area where we have the highest visual acuity

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27
Q

Name cranial nerve 2

A

The optic nerve

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28
Q

Where does the optic nerve exit the retina from?

A

The optic disk

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29
Q

What is social about the otic disk

A

There are no photoreceptors in that area (the human blindspot)

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30
Q

What is the cornea a major area of?

A

Refraction

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31
Q

What is the retina an extension of?

A

The diencephalon

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32
Q

What can the retina be split into?

A

a non-neuronal and a neuronal layer.

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33
Q

What does the non-neuronal layer consist of?

A

PIgmented epithelium

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34
Q

Where is the non-neuronal layer found?

A

It Sits against the choroid and is light absorbing.

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35
Q

What does the pigmented epithelium of the retina do?

A

It absorbs light first

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36
Q

What does the neural layer consist of?

A

Photoreceptors, bipolar cells, ganglion cells

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37
Q

What do the cells of the pigmented epithelium connect to ?

A

the first Neurones:

The photoreceptor part of the neural layer

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38
Q

What are the 2 types of photoreceptors called?

A

Rods

Cones

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39
Q

What do the photoreceptors cells connect to ?

A

Bipolar cells

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40
Q

What do the bipolar cells connect to ?

A

Ganglion cells

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41
Q

What do the axons of the ganglion cells exit as?

A

The optic nerve

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42
Q

What is an interneurone

A

A neurone that connects one neurone to another

43
Q

Name the interneurones present in the retina

A
  1. Amacrine

2. Horizontal

44
Q

What are all the neurone connections in the retina essentially doing?

A

Helping transmit the electrical information from light into electrochemical information of action potentials

45
Q

Where is the blind spot in our eye?

A

At the optic disk

46
Q

What are photoreceptors?

A

They are neurones specialised in interpreting light information that comes through our eyes

47
Q

How are rods and cones distributed in our eyes?

A

They are heterogeneously expressed across the retina

48
Q

Name an area of the eye where only cones are expressed

A

The macula

49
Q

Which type of photoreceptor is the most common?

A

Los are 20times more common than cones

50
Q

Describe rods

A

They are Sensitive to light
Good Vision in dimlight
Have a High level of convergence

51
Q

Describe cones

A

Give us colour vision
Have a high visual acuity
Have a lower level of convergence than rods

52
Q

What are cones important for

A

Giving is colour vision and high visual acuity

53
Q

Where are cones concentrated?

A

At the macula

54
Q

Where is the macula found?

A

Middle of the fovea

55
Q

How many neurones make up the pathway from the photoreceptors to the cortex?

A

3 Neurone chain

56
Q

Where are the 1st and second neurones of the visual pathway found?

A

In the retina

57
Q

Name the 1st neurone of the visual pathway

A

Bipolar cells

58
Q

Name the 2nd neurone of the visual pathway

A

Ganglion cells

59
Q

Where does the optic nerve project after leaving the retina?

A

Once it exits the retina via the optic disk the optic nerve projects to thalamus

60
Q

What area of the thalamus does the optic nerve connect to?

A

The lateral geniculate nucleus (LGN)

61
Q

What happens to the lateral geniculate nucleus?

A

It is where the optic nerve synapses with the third neurone of the pathway

62
Q

After the synapsing the the lateral geniculate nucleus where does the impulse travel?

A

From the thalamus to the cerebral cortex via optic radiation

63
Q

What is the optic nerve?

A

It is an outgrowth from the diencephalon so it is actually part of the CNS.

64
Q

Since the optic nerve is an extension of the CNS what is it surrounded by?

A

Meninges surrounding it to the eyeball.

65
Q

Name the 3 layers of meninges

A

Dura
Arachnoid
Pia

66
Q

What does a rise in cerebral spinal fluid pressure lead to?

A

Papilloedema

67
Q

What is Papilloedema?

A

A swelling of the optic disk due to the increase in CSF pressure

68
Q

What does Papilloedema lead to?

A

Increase in pressure compresses the central retinal vein preventing venous drainage from the eye
resulting in major swelling

69
Q

What are some symptoms of papilloedema?

A

Head aches
Drowsiness
Blurred vision
Vomiting

70
Q

After exiting the retina what do the pair of optic nerves do?

A

They merge at the optic chiasma

71
Q

Where do the 2 optic nerves merge once exiting the retina?

A

The optic chiasma

72
Q

What happens at the optic chiasma?

A

The 2 optic nerves meet and some of the fibres from the left and right nerves cross over to the other side
Some fibres will not

73
Q

What is the crossing over of SOME fibres called and where does it occur?

A

It is called Hemidecussation
of fibres
and it occurs at the optic chiasma

74
Q

Where do the fibres travel after leaving the optic chiasma?

A

The fibres travel along the optic tract to our Lateral
geniculate
nucleus of
thalamus

75
Q

What happens to the fibres after reaching the lateral geniculate nucleus?

A

From the thalamus the fibres travels the primary visual cortex vis the optic radiations

76
Q

How is the visual pathway organised?

A

It os retinotopically organised

77
Q

What does it mean when we say the visual pathway is retinotopically organised?

A

Visual info is going to be segregated into different specific ways all along the pathway

78
Q

Where does the left half of the visual field go?

A

To the right hemisphere

79
Q

Where does the RIGHT half of the visual field go?

A

To the left hemisphere

80
Q

Where does the upper visual field go?

A

To the lower bank of calcarine sulcus

81
Q

Where does the lower visual field go?

A

To the upper bank of calcarine sulcus

82
Q

Where does the centre of the visual axis (macula) go?

A

Goes to the occipital pole

83
Q

What happens to our visual field in the retina?

A

The images from the visual field are inverted onto the retinal fields: upside down and mirror reversed

84
Q

Which fibres cross at the optic chiasm?

A

Nasal fibres cross

85
Q

Which fibres don’t cross at the optic chiasm?

A

Temporal don’t

86
Q

Where are your nasal fibres?

A

They are the fibres Medial to the fovea

87
Q

Where are your temporal fibres?

A

They are the fibres Lateral to the fovea

88
Q

Where are the upper and lower visual fibres separated?

A

At the Lateral geniculate nucleus (LGN)

89
Q

Where do the fibres from the lower visual field travel?

A

Along the superior trajectory to the upper bank of the Calcarine sulcus

90
Q

Where do the fibres from the superior visual field travel?

A

Inferior trajectory/Meyer’s loop to the lower bank of the Calcarine sulcus

91
Q

What is another name for the inferior trajectory?

A

Meyer’s loop

92
Q

Where are fibres fro the macula represented in the primary visual cortex?

A

Most posteriorly (towards the tip of the occipital pole)

93
Q

How can vision be disrupted?

A

Vision can be disrupted due to damage to the visual pathway at it passes from the retina to the cerebral cortex.

94
Q

What is a scotoma?

A

localised patch of blindness

95
Q

What is an anopia?

A

Refers to the loss of one or more quadrants of the visual field

96
Q

What are the 2 types of anopia called?

A

Hemianopia

Quadrantanopia

97
Q

What is Quadrantanopia?

A

A type of anopia where by a quarter of the visual field is lost

98
Q

What is Hemianopia?

A

A type of anopia where by half of the visual field is lost

99
Q

What is Homonymous?

A

When Visual field losses are similar for both sides

100
Q

What is Heteronymous?

A

When Visual field losses are on different sides

101
Q

What is the clinical condition associated with a localised patch of blindness?

A

Scotoma

102
Q

What is the clinical condition associated with losing Half of the visual field?

A

Hemianopia which is a type of anopia

103
Q

What is the clinical condition associated with losing a quarter of the visual field?

A

Quadrantanopia which is a type of anopia