Visual Pathways

Question 1

how many rods are there

Answer 1

130 million

Question 2

what type of vision do rods provide

Answer 2

• black and white
• dim
• peripheral

Question 3

three components of rods

Answer 3

• inner
• outer (700 discs, contains rhadapsin)
• rod fibre (nucleus)

Question 4

what does rhadapsin do

Answer 4

inhibits glutamate which is continuously secreted in darkness

Question 5

what type of vision do cones provide

Answer 5

• colour
• bright light

Question 6

how do cones work

Answer 6

3 types - each contain a different pigment to allow for the absorption of red, green and blue light

Question 7

2 components of cones

Answer 7

• inner
• outer (pigment-bearing discs)

Question 8

midget cells

Answer 8

• small dendritic arbors
• small slow moving nuclei
• not sensitive to low contrast
• colour

Question 9

parasol cells

Answer 9

• large dendritic arbors
• large fast moving nuclei
• not sensitive to low contrast
• colour

Question 10

name 3 association neurons

Answer 10

• amacrine cells
• horizontal cells
• interplexiform cells

Question 11

amacrine cells function

Answer 11

inhibitory and exitatory

Question 12

horizontal cells function

Answer 12

inhibitory

Question 13

interplexiform cells functon

Answer 13

feedback between amacrine and horizontal cells

Question 14

muller glial cells function

Answer 14

support

Question 15

pathway to visual cortex

Answer 15

optic nerve → optic chiasm (hypothalamus) - visual fields cross → lateral geniculate nucleus of the thalamus

Question 16

name the four portions of the optic nerve

Answer 16

• intraocular portion
• intraorbital portion
• intracanalicular portion
• intracranial portion

Question 17

where is the optic tract and chiasm found

Answer 17

superior to the sella turcica and therefore the pituitary gland which it contains

Question 18

what is the optic tract and chiasm susceptible to

Answer 18

secondary pituitary disorders

Question 19

what is the pulvinar nucleus

Answer 19

Most fibres travel from the chiasm after splitting to lateral geniculate nucleus but 10% travel to superior colliculus and pulvinar nucleus and from here to the primary visual cortex

Question 20

where is the pulvinar nucleus found

Answer 20

• thalamus - largest thalamic nucleus (25% of thalamus size)
• medial and dorsal to lateral geniculate nucleus

Question 21

what is the lateral geniculate nucleus

Answer 21

6 layered structure:
4 parvocellular layers
2 magnocellular layers

Question 22

what do the parvocellular layers receive input from

lateral geniculate nucleus

Answer 22

midget ganglion cells

Question 23

what do the magnocellular layers recive input from

Answer 23

parasol cells

Question 24

what are optic radiations

Answer 24

geniculocalcarine fibres

Question 25

optic radations pathways

Answer 25

- exit dorsally from the lateral geniculate nucleus, then spread into two major bundles (superior and inferior) - The dorsal and central bundles travel in parietal lobe to the visual cortex - The ventral group (meyer’s loop) of fibres curves in an anteroinferior direction into the anterior pole of the temporal lobe

Question 26

information processed in primary visual cortex

Answer 26

- static vs moving objects - pattern recognition

Question 27

where are the second visual cortices found

Answer 27

- occipital lobe - parietal lobe - temporal lobe

Question 28

information processes in secondary visual cortices

Answer 28

- object recognition - colour perception - depth - motion

Question 29

two types of visual defects due to interruptions of the pathway at the retina

Answer 29

- retinal deachment - colour vision deficiency

Question 30

explain retinal detachment

Answer 30

- due to blow to the eye or spontaneously - fluid accumulation - can lead to blindness

Question 31

explain colour vision deficiency

Answer 31

- dichromatic vision: one opsin not produced - monochromatic vision: 2 opsins not produced

Question 32

four visual defects due to interruptions of the pathway at the optic pathway

Answer 32

- monocular blindness - bitemporal hemianopia - homonymous hemianopia - lesions of primary visual cortex

Question 33

explain monocular blindness

Answer 33

- lesion at optic nerve - stroke (ophthalmic artery) - migraine (transient) - multiple sclerosis (bilateral)

Question 34

explaim bitemporal hemianopia

Answer 34

- optic nerve compresson - pituitary tumour - information from temporal visual fields falls on nasal retina - vision is missing in outer half of both left and right visual field

Question 35

homonymous hemianopia

Answer 35

- posterior cerebral artery stroke - lesion in optic chiasm - vertical midline loss

Question 36

lesiond of primary visual cortex

Answer 36

- scotoma - hole in visual field