Primary Visual Pathway

Question 1

What forms the optic nerve?

Answer 1

~1.2 million retinal ganglion cell axons (80–90% small/midget type).

Question 2

What are the three meningeal sheaths surrounding the optic nerve?

Answer 2

Dura mater, arachnoid mater, and pia mater (with subarachnoid space).

Question 3

What is the approximate total length of the optic nerve?

Answer 3

About 5 cm.

Question 4

What are the three portions of the optic nerve and their lengths?

Answer 4

Intraorbital (25 mm), intracanalicular (5 mm), intracranial (extends to chiasm).

Question 5

Where is the optic nerve head (ONH) located relative to the macula?

Answer 5

15° nasal and slightly superior.

Question 6

Why is the optic nerve head a blind spot?

Answer 6

It contains no photoreceptors.

Question 7

When does myelination of the optic nerve begin?

Answer 7

After the lamina cribrosa (post-laminar).

Question 8

What structure provides support to the optic nerve with 200–400 pores?

Answer 8

The lamina cribrosa.

Question 9

What supplies the optic nerve head? (Blood supply)

Answer 9

Short posterior ciliary arteries via the Circle of Zinn.

Question 10

What supplies outer optic nerve fibres? (Blood supply)

Answer 10

Pia mater vascular plexus.

Question 11

What does the central retinal artery supply? (Blood supply)

Answer 11

Central nerve fibres and superficial disc capillaries.

Question 12

Which retinal fibres cross at the optic chiasm?

Answer 12

Nasal retinal fibres.

Question 13

Which fibres remain ipsilateral?

Answer 13

Temporal retinal fibres.

Question 14

What is the anterior looping of nasal fibres before crossing called? (Optic Chiasm)

Answer 14

The Anterior Knee of Wilbrand.

Question 15

Where do the optic tracts project?

Answer 15

From the chiasm to the lateral geniculate nucleus (LGN).

Question 16

Which fibres branch off early to the superior colliculus? (Optic Tract)

Answer 16

Fibres for the pupillary light reflex.

Question 17

The LGN is part of which brain structure?

Answer 17

The thalamus.

Question 18

How many main LGN layers are there?

Answer 18

Six layers plus koniocellular layers in between.

Question 19

Does each LGN layer receive input from one eye or both?

Answer 19

Only one eye per layer.

Question 20

Which LGN layers are magnocellular?

Answer 20

Layers 1 and 2.

Question 21

Which magnocellular layer receives contralateral input? (LGN)

Answer 21

Layer 1.

Question 22

Which magnocellular layer receives ipsilateral input? (LGN)

Answer 22

Layer 2.

Question 23

Which layers are parvocellular? (LGN)

Answer 23

Layers 3–6.

Question 24

Parvocellular layers receiving ipsilateral input?

Answer 24

Layers 3 and 5.

Question 25

Parvocellular layers receiving contralateral input?

Answer 25

Layers 4 and 6.

Question 26

Characteristics of magnocellular pathway? (LGN)

Answer 26

Parasol cells; achromatic; high temporal frequency; low contrast sensitivity.

Question 27

Characteristics of parvocellular pathway? (LGN)

Answer 27

Midget cells; red/green opponency; high spatial resolution.

Question 28

Characteristics of koniocellular pathway? (LGN)

Answer 28

Bistratified cells; blue/yellow opponency; low spatial/temporal resolution.

Question 29

What are optic radiations?

Answer 29

Projections from the LGN to the primary visual cortex (V1).

Question 30

Which fibres loop into the temporal lobe (Meyer’s Loop)?

Answer 30

Inferior optic radiations.

Question 31

Meyer’s Loop carries visual information from which field?

Answer 31

Superior visual field.

Question 32

Damage to Meyer’s Loop causes what defect?

Answer 32

Contralateral superior quadrantanopia.

Question 33

What do the superior optic radiations carry?

Answer 33

Inferior visual field information.

Question 34

All major cerebral arteries arise from what?

Answer 34

The Circle of Willis.

Question 35

The ophthalmic artery branches from which artery?

Answer 35

The internal carotid artery.

Question 36

What do anterior and middle cerebral arteries supply?

Answer 36

Anterior and temporal cortex.

Question 37

What does the posterior cerebral artery supply?

Answer 37

Occipital cortex, including V1.

Question 38

Where is V1 located?

Answer 38

Occipital lobe around the calcarine sulcus.

Question 39

How many layers does V1 have?

Answer 39

Six (striate appearance).

Question 40

Which V1 layer is the main input layer from the LGN?

Answer 40

Layer 4C.

Question 41

Which sublayer receives magnocellular input?

Answer 41

4Cα.

Question 42

Which sublayers receive parvocellular input?

Answer 42

4A and 4Cβ.

Question 43

Which V1 layers project to higher cortical areas?

Answer 43

Layers 2, 3, and 4B.

Question 44

Which layers project to subcortical structures (e.g., superior colliculus)?

Answer 44

Layers 5 and 6.

Question 45

What are ocular dominance columns? (cortical columns)

Answer 45

Columns where input is segregated by eye.

Question 46

What are orientation columns? (cortical columns)

Answer 46

Columns selective for stimulus orientation.

Question 47

How are cortical columns arranged?

Answer 47

Orthogonally, extending through cortical depth.

Question 48

Which part of V1 represents the fovea?

Answer 48

The posterior tip (large representation).

Question 49

Where is the peripheral visual field represented in V1?

Answer 49

More anterior portions.

Question 50

On the calcarine sulcus, which bank represents the inferior visual field?

Answer 50

Upper bank.