Vision

Question 1

Three layers of the eye, outside to inside

Answer 1

sclera, choroid, retina

Question 2

Developmental history of the eye

Answer 2

Part of the diencephalon, called to optic cup, anatomically part of the CNS

Question 3

outer segment

Answer 3

where the detection of light occurs

Question 4

outer nuclear layer

Answer 4

alignment of the nuclei for the receptor

Question 5

outer plexiform layer

Answer 5

first synapses with the bipolar and horizontal cells

Question 6

inner nuclear layer

Answer 6

soma and nuclei of bipolar cells

Question 7

inner plexiform layer

Answer 7

bipolar cells synapses with ganglion cells (also contains amincrine cells)

Question 8

ganglion cells

Answer 8

projection neurons with long axonal projections that travel in the nerve fiber layer and exit the eye at the optic disc to form the optic nerve

Question 9

phototransduction

Answer 9

the conversion of a light stimulus to a voltage response. in the dark - 40 mV. light causes a HYPERPOLARIZATION. light causes the cGMP-gated channel to close, this hyperpolarizes the membrane because the K+ outflow channel is still active

Question 10

photopigments

Answer 10

11-cis retinal bound to an opsin (G protein coupled membrane receptors in the outer discs). activated when converted to all-trans retinal (retinal comes from beta carotene in the diet –> cleaved to all-trans retinal then can be cleaved to retinol or vitamin A)

Question 11

Opsins

Answer 11

Rods: rhodopsin (peak absorption is blue/green). Cones: 3 types, L (red), M (green), S (blue)

Question 12

rod outer segment 1 photon

Answer 12

can cause 1 mV hyperpolarization

Question 13

retinal pigment epithelium

Answer 13

outermost layer of the retina, has special supportive roles for photoreceptors

Question 14

retinoid recycling

Answer 14

all-trans retinal dissociates from the activated opsin —> becomes all trans retinOL –> binds to IRBP –> endocytosed by the retinal pigment epithelium –> conversion to 11-cis retinal and oxidation to retinal —> 11-cis IRBP complex is then shuttled to a photoreceptor

Question 15

disc removal

Answer 15

lifetime of a disc: 12 days. phagocytosed by the retinal pigmented epithelium

Question 16

L and M opsins

Answer 16

closely related on the x-chromosome (high chance of crossover, deletion, or duplication). red/green colorblindness is very common in men. perception of red versus green is ambiguous

Question 17

Cones

Answer 17

location: central (fovea), abundance: 5%, opsins: L, M, S, convergence on to bipolar cell: 1 to 1, sensitivity: low (bright light), response time: fast, functional role: central vision, color discrimination in bright light, fine spatial resolution 1:1 relation with bipolar cells.

Question 18

retinitis pigmentosa

Answer 18

degenerative disease caused by the progressive loss of rods over decades causing pigment changes in the retina. symptoms include poor vision in low light conditions or “night blindness” and peripheral vision restriction

Question 19

rods

Answer 19

location: periphery, abundance: 95%, opsins: rhodopsin, convergence on to bipolar cell: 100 to 1, sensitivity: high (dim light), response time: sluggish, functional role: peripheral vision, monochromatic, sensitive to dim light, poor spatial resolution

Question 20

receptive field

Answer 20

the region of the body that when appropriately stimulated elicits a action potential

Question 21

ganglion cell receptive field

Answer 21

the location on the retina that elicits a action potential when appropriately stimulated by light. the receptive field is smallest in the fovea

Question 22

simulation of the surround…

Answer 22

produces a response that opposes the center

Question 23

photoreceptors release what, when?

Answer 23

glutamate, in the dark

Question 24

the determination of on/off behavior is set by…

Answer 24

the bipolar cell based on it’s response to glutamate (which is high in the OFF state). On center bipolar cells has mGluR6 (cause cGMP gate closure when stimulated by glutamate). OFF center bipolar cells have AMPA and kainite receptors (outer plexiform synapse) which causes depolarization in response to high glutamate.

Question 25

lateral inhibition: horizontal cells

Answer 25

projections in the outer plexiform layer, in response to glutamate, release at inhibitory GABA-ergic synapses. Inhibition by one cells to it’s cells on opposite sides

Question 26

two benefits of lateral inhibition

Answer 26

1. amplifies local differences 2. provides a mechanism to adapt to the background level of illumination (extend the range of brightness level based perception levels)

Question 27

rod based vision, cone based vision, mix of both

Answer 27

scotopic, photopic, mesopic (moonlight)

Question 28

change in surround inhibition

Answer 28

allows for sensory adaptation

Question 29

two ways for sensory adaptation to occur in the eye

Answer 29

1. changes in surround inhibition 2. modulation of the phototransduction process via a constant increased light level –> causes a decrease in intracellular Ca2+ which increases cGMP affinity, a higher level of cGMP (through increased guanylate cyclase activity), increased rhodopsin kinase activity

Question 30

Images are…

Answer 30

FLIPPED as they enter the retina (plz don’t forget this)

Question 31

retino-geniculo-calcarine pathway

Answer 31

retina —> lateral geniculate —> primary visual cortex