week 35 visual pathway

Question 1

what is the visual pathway?

Answer 1

the route by which retinal stimuli is transferred to the occipital cortex of the brain from the retina

Question 2

at which point will damage affect vision?

Answer 2

at any point along the pathway

Question 3

what are the key structures of the pathway?

Answer 3

optic nerve
optic chiasm
optic tract
LGN
optic radiations
visual cortex

Question 4

what are the associated structures?

Answer 4

pituitary gland
edinger-westphal nucleus
circle of wilis

Question 5

how many neurons are in the pathway?

Answer 5

3

Question 6

how many synapses?

Answer 6

2

Question 7

where are the synapses located?

Answer 7

between bipolar and ganglion cells in the retina
at the LGN

Question 8

what is the arrangement of nerve fibres in the optic nerve?

Answer 8

at the start, they arranged based on the retinal location
rearranged towards the end so macula fibres in the centre

Question 9

which side of the visual field is each eye responsible for?

Answer 9

each eye forms an image of both the right and left side of the visual field
visual field therefore duplicated on the retina of both the right and left eye

Question 10

what happens at the optic chiasm?

Answer 10

all info is sorted so all fibres transmitting info from the right visual field is together and same for the left

Question 11

how do the nasal and temporal retinas work together?

Answer 11

nasal retina from one eye joins with info from the temporal retina of the other

Question 12

what is the crossing of info from temporal to nasal called?

Answer 12

decussation

Question 13

what happens to retinal fibres at the optical chiasm?

Answer 13

inferior retinal fibres cross anteriorly
superior fibres cross posteriorly

Question 14

what are the groups of visual defects called?

Answer 14

pre-chiasmal
chiasmal
post-chiasmal

Question 15

what happens with a pre-chiasmal lesion?

Answer 15

affects the visual field on the affected side

Question 16

what would a RE pre-chiasmal lesion affect?

Answer 16

RE visual field

Question 17

what happens with post-chiasmal lesions?

Answer 17

visual field of both eyes are affected

Question 18

what happens with chiasmal lesions?

Answer 18

bi-temporal hemianopia
loss of peripheral vision

Question 19

what is the circle of Willis?

Answer 19

connecting ring of arteries that supply the brain
an aneurysm in the internal carotid artery can press agaonst the chiasm

Question 20

where is the pituitary gland located?

Answer 20

sits below the chiasm

Question 21

what happens with a pituitary adenoma?

Answer 21

can press on the chiasm from below

Question 22

where does the optic tract extend from and to?

Answer 22

from posterior chiasm to the LGN

Question 23

what happens at the optic tract?

Answer 23

nerve fibres representing the right side visual field now together on the left of the pathway and vice-versa

right nasal and left temporal retina together

rearrangement of fibres so macula fibres now at the top

Question 24

what happens if there is damage on the optic tract?

Answer 24

blindness in ipsilateral half of the visual field

Question 25

what are the features of the LGN?

Answer 25

pair of nuclei so a site of a synapse folded over horse shoe shape six layers

Question 26

where is the dorsal aspect of the LGN?

Answer 26

outside of the curve

Question 27

where is the ventral aspect of the LGN?

Answer 27

inside of the curve

Question 28

what is the nerve fibre arrangement in the LGN?

Answer 28

nerve fibre arrangement of optic tract reflected in LGN retinotopic arrangement macula fibres centrally layers 2,3&5 have uncrossed fibres from the ipsilateral eye layers 1,4&6 have crossed fibres from contralateral eye

Question 29

what does ipsilateral eye mean?

Answer 29

eye is located on the same side of the body as the object or structure

Question 30

what does contralateral eye mean?

Answer 30

eye is located on the opposite side of the body as the object or structure

Question 31

what are the features of layers 1 and 2 of the LGN?

Answer 31

large cells magnocellular contrast, low light, visual search

Question 32

what are the features of layers 3,4,5&6 of the LGN?

Answer 32

small cells parvocellular colour and detail

Question 33

features of optic radiations?

Answer 33

nerve fibres extend to parietal and temporal lobes potential for some parts to be affected by lesions some remain intact

Question 34

where is Meyers loop and what fibres does it contain?

Answer 34

outside bundle of the radiating fibres contains fibres from the inferior retina/superior visual field inside bundle has fibres from superior retina/inferior visual field

Question 35

what happens to the eye if there is a lesion on the inside or outside of the loop?

Answer 35

will affect a quarter of each visual field

Question 36

what does quadrantanopia refer to?

Answer 36

loss of vision in a quarter of the visual field?

Question 37

where is the superior retina/inferior visual field in relation to the brain?

Answer 37

the parietal lobe

Question 38

where is the inferior retina/superior visual field in relation to the brain?

Answer 38

the temporal lobe

Question 39

what happens if there is a lesion on the posterior part of optic radiations?

Answer 39

half-field defects hemianopia

Question 40

features of primary visual cortex?

Answer 40

fibres project to different areas of the cortex depending on origin and purpose macular fibres take up the most space

Question 41

what is a congruous defect?

Answer 41

similar defect in both eyes

Question 42

what is a macular sparring defect?

Answer 42

hemianopia defect but the area around the macula is unaffected

Question 43

what artery supplies blood to retina and extra-cranial optic nerve?