Visual Pathways Flashcards
What is the ring of glial tissue that separates the retinal layers and the optic nerve?
Intermediary tissue of Kuhnt
What is the ring of fibrous tissue that separates the choroid and sclera from the optic nerve?
Marginal/border tissue
Out of the RPE, Bruch’s membrane and the choroidal vascular layers, which two go up to the optic nerve?
RPE and Bruch’s membrane
What is the scleral canal? How long is it?
The point where the optic nerve passes through the sclera
0.5mm long
What are the three shapes that the scleral canal could be?
Cone (narrowest at Bruch’s membrane)
Cylinder (even diameter)
X (narrowest in centre)
How many fibres does the optic nerve contain?
~1 million
Where does myelination of the optic nerve normally start?
At the lamina cribosa
What three types of fibres are within the optic nerve?
Visual
Pupillary
Centrifugal (retino-motor)
How many nerve bundles is the optic nerve separated into? What separates them?
800-1200
Septa or glial tissue separates
What separates the ventromedial and dorsolateral portions of the optic nerve?
Triangular septum
What are the meninges of the optic nerve, from inner to outer?
Pia mater
Arachnoid
Dura mater
What are the characteristics of the pia mater?
Tough and fibrous
Elastic fibres (outer: circular, inner: longitudinal)
Highly vascularised
It’s continuous with the central retinal artery, arterial wall and septa
What are the characteristics of the arachnoid?
Very thin
Collagenous
What are the characteristics of the dura mater?
Tough and fibrous
Elastic fibres, continuous with sclera (inner: circular, outer: longitudinal)
Where is the chiasm located and what surrounds it?
Above pituitary fossa
Surrounded by pia mater and CSF
What are the secondary visual pathways?
Superior colliculus: Eye movements
Suprachiasmatic nucleus: Circadian rhythms
Pretectum to Edinger Westphal nucleus: Pupillary light reflex, accommodation
Accessory optic nuclei: visual flow
What are some features of the optic tract?
Not attached to anything near chiasm, but attached to third ventricle wall
Cylindrical then flattens slightly
Where is the LGN located?
Anterior lateral thalamus
Which layers of the LGN contain information from the ipsilateral eye?
2, 3, 5
Which layers of the LGN contain information from the contralateral eye?
1, 4, 6
Which layers of the LGN contain magnocellular information?
1, 2
Which layers of the LGN contain parvocellular information?
3, 4, 5, 6
Which layers of the LGN contain koniocellular information?
Between magno and parvo layers
What inputs does the LGN have?
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)
Which field do the upper/inner radiations relate to?
Inferior visual field (superior retina)
Which field do the lower/outer radiations/Meyer’s loop relate to?
Superior visual field (inferior retina)
What is V1 also known as?
Striate cortex
Brodmann’s Area 17
What is the Line of Gennari?
Myelination in V1 (layer 4B) which marks where V2 begins (ends there)
How many layers are there in V1?
6
Which layer of V1 does the LGN input go into?
4C
What are the 6 layers of V1?
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)
The dorsal pathway is for what?
Where - magnocellular - movement
The ventral pathway is for what?
What - parvocellular - detail
