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The Optic Pathway Flashcards

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Biology 101 flashcards
0
Q

Where do the axons of retinal ganglion cells end up?

A

With excitatory synapses with the lateral geniculate nucleus

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1
Q

Which cell forms the origin of the optic pathway?

A

Retinal ganglion cells

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2
Q

Briefly describe order of the optic pathway

A

From retinal ganglion cell axons from back of eye travel down the optic nerve, through a junction called the optic chiasm into the optic tract and to the nucleus of the thalamus called the LGN

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3
Q

How much % of retinal ganglion cell axons end up in the LGN?

A

90%

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4
Q

How long is the optic nerve all together?

A

30-50mm long

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5
Q

Name the 4 consecutive regions of the optic nerve

A
  1. Intra ocular
  2. Intra orbital
  3. Intra canalicular
  4. Intra cranial
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6
Q

How long is the intra canalicular consecutive region

A

5mm

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7
Q

How long is the intra orbital consecutive region

A

20-30mm

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8
Q

How long is the intra ocular consecutive region

A

1mm

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9
Q

How long is the intra cranial consecutive region

A

5-15mm

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10
Q

Which is the shortest consecutive region

A

Intra ocular

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11
Q

Which is the longest consecutive region

A

Intra orbital

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12
Q

Where is the intra ocular consecutive region found

A

Inside the eye

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13
Q

Where is the intra cranial consecutive region found

A

Inside the skull

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14
Q

Where does the intra cranial consecutive region head towards

A

Optic chiasm

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15
Q

What does the intra canalicular consecutive region go through

A

The hole at the back of the orbit through the canal

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16
Q

What is the intra ocular consecutive region known as

A

Optic nerve head

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17
Q

What leaves through the optic nerve head

A

Axons of retinal ganglion cells

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18
Q

Which region of the retina is the optic nerve head found

A

Nasal retina

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19
Q

Which main artery and vein do arteries coming in and veins going out branch off from?

A

Central retinal artery and central retinal vein

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20
Q

Which region of the optic nerve head of the veins and arteries of the central retinal artery and vein enter and exit from

A

Nasal side

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21
Q

Why do the veins and arteries exit and enter nasally on the optic nerve head?

A

As macula and fovea are at the temporal side of the retina where blood vessels skirt this region

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22
Q

What part of the optic nerve head is visible with the ophthalmoscope

A

Optic disc

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23
Q

What’s the normal range of the variable disc area?

A

0.90-5.5mm squared mean 2.7mm squared

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24
Q

How many % of normal subjects do an indentation or cup occur

A

75%

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25
Q

In which case would the obvious indentation or cup not be the same in both eyes of the same individual be

A

Pathological

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26
Q

What is surrounding the indentation or cup?

A

Neuroretinal rim

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27
Q

Why should you look for bilateral asymmetry in cup and disc sizes

A

Indicates something’s gone wrong eg pathological change

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28
Q

What is pallor

A

Pale optic disc due to water building up behind optic nerve head = oedema

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29
Q

How many ganglion cell axons run in the nerve fibre layer on the inner retinal surface

A

1 million

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30
Q

Where in the retina is the nerve fibre layer found

A

Inner retinal surface

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31
Q

Which retinal quadrants do ganglion cells take direct course to the nerve head?

A

Nasal
Superior
Inferior

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32
Q

From which region of the retina do ganglion cells take an arcuate course

A

Temporal

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33
Q

What do the temporal retinal ganglion axons arc around

A

Fovea centralis

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34
Q

From where to where do the arcuate ganglion axons go to

A

Temporal retina to the macula

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35
Q

What is the papillomacular bundle

A

Axons from temporal ganglion cells nearer the nerve head

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36
Q

What do ganglion cell axons pass through when they leave the eye

A

Lamina cribrosa

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37
Q

What is the lamina cribrosa

A

Modified region of sclera and compact perforated connective tissue plates layed down in sheets

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38
Q

What does the lamina cribrosa contain

A

Numerous pores in a sieve like arrangement

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39
Q

What does the lamina cribrosa do

A

Holds axons together and provides them with mechanical support prior to entering the the intra orbital part of the nerve

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40
Q

Why do ganglion cell axons need support from the lamina cribrosa

A

Because they are delicate floppy and flimsy

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41
Q

What does the lamina cribrosa also supply other than support to the ganglion cell axons

A

Useful reference point on the optic nerve head

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42
Q

How many segments does the lamina cribrosa divide into

A

Three

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43
Q

What are the names of the distinct segments that lamina cribrosa divides into

A
  1. Pre laminar
  2. Laminar
  3. Post laminar
    Regions
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44
Q

Why is the nerve fibre layer big and elevated at the neuro retinal rim?

A

Due to accumulating retinal axons traveling down the optic nerve fibre layer and exiting the eye

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45
Q

What does the pre laminar segment of the ONH consist of

A

The nerve fibre layer & supporting astrocytes which go all the way down to the brain

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46
Q

What type of cell is an astrocyte

A

Glial cell

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47
Q

What else apart from the lamina cribrosa support the axons

A

Astrocytes

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48
Q

What does the laminar segment of the ONH consist of

A

Supporting connective tissue & pores

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49
Q

What does the post laminar segment of the ONH consist of

A

Wide diameter axons myelinated by oligodendrocytes and wider nerves which have meninges and lots of astrocytes all the way down the ONH to the brain

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50
Q

Why are the pores wider at the post laminar segment that the laminar at the ONH

A

Because the axons at the post laminar region acquire a myeline sheath so has lots of oligodendrocytes down the myeline causing wider diameter & the edge surrounding the nerve requires the meninges which increases it’s diameter

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51
Q

Describe the appearance of an astrocyte

A

A cell body with lots of fine processes and feet which come out with a star like arrangement

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52
Q

Which part of the nervous system are glial cells resident

A

All parts

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53
Q

What do the pre laminar segment of the ONH form borders with

A

Vitreous = inner limiting membrane of elsching (special astrocytes which connects to the inner limiting membrane which separates the retina with vitreous)
&
Outer retina and choroid tissues of kuhnt & jacoby (astrocytes which seal part of the choroid with the sclera axons if ganglion cells)

54
Q

Where in the pathway are astrocytes found

A

Everywhere

55
Q

What do astrocytes do for retinal axons

A

Provides mechanical support and separates them into bundles

56
Q

What is the name of the bundles of retinal axons formed by astrocytes

A

Fascicles

57
Q

What do astrocytes wrap around in the optic pathway

A

Capillaries

58
Q

What barrier is formed when astrocytes wrap around capillaries in the optic pathway

A

Blood nerve barrier called carivascular endfeet

59
Q

What do astrocytes do in response to injury of the optic pathway

A

Proliferate (divide) and form scar tissue

60
Q

What is the lamina cribrosa composed of

A

Elastin
Laminin and
Collagen

61
Q

What do the pores of the lamina cribrosa transmit

A

Axon bundles or fascicles to pass through

62
Q

Describe the pore diameters of the lamina cribrosa

A

Larger in inferior and superior regions with corresponding reduced supporting connective tissue
Smaller in nasal and especially temporal region

63
Q

What is the susceptibility to risk to the axons in the different pure sizes of the lamina cribrosa

A

Larger size pore = less mechanical support to axons

So temporal region containing the papillomacular bundle is least at risk (hence periphery visual loss with glaucoma)

64
Q

What rule is followed of decreasing axon damage susceptibility of the pores of the lamina cribrosa

A

ISNT

Inferior is larger than superior is larger than nasal is larger than temporal

65
Q

What causes cupping of the ONH

A

Raised iop due to failure of aqueous drainage

66
Q

Where does the pressure try to escape through in the eye with raised iop

A

The optic nerve head

67
Q

Which area of nerves are initially most vulnerable in the lamina cribrosa due to raised iop

A

Inferior which has least support of axons

68
Q

Which area of visual field is lost due to damage to the inferior lamina cribrosa

A

Superior visual field loss

69
Q

Which type of glaucoma is associated with raised iop

A

Both open and closed angle

70
Q

From the pre laminar to the post laminar region of the ONH, by how much does the optic nerve increase

A

Double from 1.5-3mm

71
Q

What are oligodendrocytes

A

Few branching cells which repeatedly wrap around axons to form myelin sheaths

72
Q

What is the composition of the three layer meningeal sheath of the post laminar nerve

A

Pia
Arachnoid
Dura

73
Q

What is continuous with the pia mater peripherally

A

Axon bundles supported by connective tissue septa formed by collagen fibres and astrocytic processes

74
Q

Where is the dura mater found

A

In the outer layer, continuous anteriorly with the sclera

75
Q

What is the dura mater comprised of

A

Thick and tough collagenous layer (lots of collagen fibres)

76
Q

What does the dura mater provide

A

Support for the whole of the optic nerve

77
Q

What does the arachnoid mater comprise of

A

Numerous trabeculae of collagen surrounded by flattened meningothelial cells

78
Q

Where is the arachnoid mater located in relation to the dura and pia maters

A

Inbetween

79
Q

Where is the pia mater located

A

Covers the inside of the optic nerve (forms a delicate inner layer)

80
Q

What is embedded within the pia septa

A

Numerous capillaries

81
Q

What does the pial septa do

A

Enter and support axons within the nerve

82
Q

What is the space between the arachnoid and pial membranes and what does it contain

A

The subarachnoid space

Cerebo spinal fluid

83
Q

As well as cerebo spinal fluid, what else does the subarachnoid space contain

A

Larger blood vessels

84
Q

What are the name of the cells which make the arachnoid mater

A

Meningothelial cells

85
Q

What do the meningothelial cells have the ability to become

A

Cancerous called meningioma

86
Q

The post laminar nerve contains

A

Bundles/fascicles of axons with connective tissue/septa in between

87
Q

What does the septa comprise of

A

Connective tissue of collagen fibres and processes that are keeping axons into bundles

88
Q

What is the subarachnoid space in the optic nerve containing the CSF continuous with

A

The ventricles containing CSF inside the brain

89
Q

What is the build up of CSF inside the ventricles of the brain called

A

Hydrocephalus

90
Q

What can hydrocephalus cause if it percolates down the space behind the brain

A

Oedema/optic disc pallor

91
Q

How many segmental blood supplies are there to the ONH

A

Three

92
Q

Which two arteries supply blood to the three segments

A

Central retinal artery &

Short posterior ciliary artery

93
Q

The sensory nerve fibre layer and pre laminar segments receive their blood supply from…

A

Branches of the central retinal artery and choroidal supply

94
Q

The segment of the lamina cribrosa receive their blood supply from…

A

Circle of zinn & haller from the short posterior ciliary artery

95
Q

The segment of the post laminar receive their blood supply from…

A

Branches of the short posterior ciliary artery running in and from the pia mater

96
Q

How much of slack does the intra orbital portion contain

A

5mm

97
Q

What is the intra orbital portion

A

Area between the optic nerve head to the optic canal (apex of orbit)

98
Q

Why is there slack within the intra orbital portion

A

Prevents trauma during eye movements eg axons from snapping when moving the eye

99
Q

What is above the optic chiasm

A

The hypothalamus and thalamus

100
Q

What is between the hypothalamus and thalamus

A

3rd ventricle (a slit)

101
Q

What does the 3rd ventricle contain

A

Cerebo spinal fluid

102
Q

What is just below the hypothalamus

A

Pituitary gland

103
Q

Where does the pituitary gland sit in relation to the optic chiasm

A

1cm below

104
Q

What things sit laterally (next to) the optic chiasm

A

Blood vessels
Internal carotid artery
Cavernous sinus

105
Q

How big is the cavernous sinus

A

Size of a grape/finger tip

106
Q

What is the cavernous sinus

A

Network of small arteries and

mainly veins

107
Q

Which sequence does the blood supply to the optic pathway have

A

Anterior - posterior

108
Q

What is the first sequence of blood supply to the optic pathway

A

Intra orbital nerve

109
Q

What is the second sequence of blood supply to the optic pathway

A

Intra canalicular nerve

110
Q

What is the third sequence of blood supply to the optic pathway

A

Intra cranial nerve and chiasm

111
Q

What is the fourth sequence of blood supply to the optic pathway

A

Optic tract (leads to LGN)

112
Q

What is the blood supply to the intra orbital nerve

A

Perforating arteries from branches of ophthalmic artery

113
Q

What is the blood supply to the intra canalicular nerve

A

Short branches from anterior cerebral and anterior communicating arteries

114
Q

What is the blood supply to the optic tract

A

Perforating thalamic branches of posterior cerebral artery

115
Q

What is the blood supply to the intra cranial nerve and chiasm

A

Short branches from posterior cerebral and posterior communicating artery

116
Q

What is the partial decussation (crossing over) of retinal axons in the chiasm

A 
Nasal crossed (goes to opposite LGN)
Temporal uncrossed
117
Q

Which side of the visual field does the right half of each eye look at

A

Left visual field

118
Q

Which side of the brain is the right hemi field linked to

A

Left

119
Q

Which side of the brain is the left hemi field linked to

A

Right

120
Q

What is the result of compression of retinal axons

A

Cannot conduct impulses anymore from the retina resulting in visual field loss

121
Q

What does a compression of the chiasm and tract at the midline cause

A

Damage to nasal axons from both eyes

122
Q

What is the cause of damage to nasal axons on both eyes

A 
Pituitary tumour (adenoma) 
Raised pressure in 3rd ventricle/hydrocephalus
123
Q

Which direction does a pituitary tumour grow

A

Upwards towards the chiasm

124
Q

How does hydrocephalus affect the chiasm

A

Pressure from CSF can crush axons crossing the midline

125
Q

What does compressions from the side of the chiasm damage

A

Damage temporal axons

Same eye

126
Q

What causes damage to the temporal axons of the chiasm

A

Internal carotid artery out pocketing (aneurysm)
&
Cavernous (compression of nasal axons) sinus expansion (thrombosis)

127
Q

What is caused from damages to nasal axons from both eyes

A

Bi temporal hemi anopia

128
Q

What does damages of temporal axons of the same eye cause

A

Uni nasal hemi anopia

129
Q

How does cavernous out pocketing cause damage to the chiasm

A

Can move to midline and crush the axons that run through that region

130
Q

Compression of the chiasm and tract can also be caused from…

A

Anywhere eg from
Meningiomas (arachnoid tumours)
Or from
Loss of blood supply (blockage or haemorrhage)

131
Q

Where do most of excitatory ganglion axons synapse/terminate

A

LGN cells of the thalamus

132
Q

The optic tract is after the…

A

Cross region

133
Q

The LGN is found at the edge of the…

A

Thalamus

Visual Science (14 decks)

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