Visual Pathways

Question 1

What is the ring of glial tissue that separates the retinal layers and the optic nerve?

Answer 1

Intermediary tissue of Kuhnt

Question 2

What is the ring of fibrous tissue that separates the choroid and sclera from the optic nerve?

Answer 2

Marginal/border tissue

Question 3

Out of the RPE, Bruch’s membrane and the choroidal vascular layers, which two go up to the optic nerve?

Answer 3

RPE and Bruch’s membrane

Question 4

What is the scleral canal? How long is it?

Answer 4

The point where the optic nerve passes through the sclera
0.5mm long

Question 5

What are the three shapes that the scleral canal could be?

Answer 5

Cone (narrowest at Bruch’s membrane)
Cylinder (even diameter)
X (narrowest in centre)

Question 6

How many fibres does the optic nerve contain?

Answer 6

~1 million

Question 7

Where does myelination of the optic nerve normally start?

Answer 7

At the lamina cribosa

Question 8

What three types of fibres are within the optic nerve?

Answer 8

Visual
Pupillary
Centrifugal (retino-motor)

Question 9

How many nerve bundles is the optic nerve separated into? What separates them?

Answer 9

800-1200
Septa or glial tissue separates

Question 10

What separates the ventromedial and dorsolateral portions of the optic nerve?

Answer 10

Triangular septum

Question 11

What are the meninges of the optic nerve, from inner to outer?

Answer 11

Pia mater
Arachnoid
Dura mater

Question 12

What are the characteristics of the pia mater?

Answer 12

Tough and fibrous
Elastic fibres (outer: circular, inner: longitudinal)
Highly vascularised
It’s continuous with the central retinal artery, arterial wall and septa

Question 13

What are the characteristics of the arachnoid?

Answer 13

Very thin
Collagenous

Question 14

What are the characteristics of the dura mater?

Answer 14

Tough and fibrous
Elastic fibres, continuous with sclera (inner: circular, outer: longitudinal)

Question 15

Where is the chiasm located and what surrounds it?

Answer 15

Above pituitary fossa
Surrounded by pia mater and CSF

Question 16

What are the secondary visual pathways?

Answer 16

Superior colliculus: Eye movements
Suprachiasmatic nucleus: Circadian rhythms
Pretectum to Edinger Westphal nucleus: Pupillary light reflex, accommodation
Accessory optic nuclei: visual flow

Question 17

What are some features of the optic tract?

Answer 17

Not attached to anything near chiasm, but attached to third ventricle wall
Cylindrical then flattens slightly

Question 18

Where is the LGN located?

Answer 18

Anterior lateral thalamus

Question 19

Which layers of the LGN contain information from the ipsilateral eye?

Answer 19

2, 3, 5

Question 20

Which layers of the LGN contain information from the contralateral eye?

Answer 20

1, 4, 6

Question 21

Which layers of the LGN contain magnocellular information?

Answer 21

1, 2

Question 22

Which layers of the LGN contain parvocellular information?

Answer 22

3, 4, 5, 6

Question 23

Which layers of the LGN contain koniocellular information?

Answer 23

Between magno and parvo layers

Question 24

What inputs does the LGN have?

Answer 24

Magnocellular (large cells and RFs - movement)
Parvocellular (small cells and RFs - detail, spatial contrast, colour)
Koniocellular (colour)
V1 (feedback, control and mapping - 80%)
Brainstem (alertness, attentiveness, arousal)

Question 25

Which field do the upper/inner radiations relate to?

Answer 25

Inferior visual field (superior retina)

Question 26

Which field do the lower/outer radiations/Meyer's loop relate to?

Answer 26

Superior visual field (inferior retina)

Question 27

What is V1 also known as?

Answer 27

Striate cortex Brodmann's Area 17

Question 28

What is the Line of Gennari?

Answer 28

Myelination in V1 (layer 4B) which marks where V2 begins (ends there)

Question 29

How many layers are there in V1?

Answer 29

6

Question 30

Which layer of V1 does the LGN input go into?

Answer 30

4C

Question 31

What are the 6 layers of V1?

Answer 31

1: Molecular (horizontal cells) 2: External granular (small pyramidal cells) 3: External pyramidal (medium pyramidal cells) 4: Inner granular (stellate cells) 5: Inner pyramidal (medium, large and giant cells) 6: Polymorphic (polymorphic cells)

Question 32

The dorsal pathway is for what?

Answer 32

Where - magnocellular - movement

Question 33

The ventral pathway is for what?

Answer 33

What - parvocellular - detail