Lecture 6

Question 1

Extramission/intermission theory

Answer 1

Extramission theory: INCORRECT
Eyes send out rays (Plato, Galen)

Intramission theory: CORRECT
Light! Input → vision

Question 2

Anatomy of the eye (see 6.2a)

Answer 2

see 6.2b

Question 3

Lens (thin vs thick, opias - 3)

Answer 3

Thick lens for distance
Thin lens for close up

Myopia: nearsighted
Hyperopia: farsighted
Presbyopia: decrease accommodation w/ age
Astigmatism: spherical abberation

Question 4

Pupil size

Answer 4

Reduced:↓ light, ↑ depth of field
Increased: ↑ light entering

Question 5

Macula & optic disk

Answer 5

Macula: High res part of retina
FOVEA in center
Optic disk: nerve fibers leaving the eye
BLINDSPOT (we “fill in”)

Question 6

Fovea

Answer 6

Center of Macula
Only CONES
Avascular
we focus the world here!

Question 7

Retinal cell types (5) & path

Answer 7

from the outside in

Photoreceptors
| Horizontal \
|→ Bipolar >sidepaths that refine
| Amacrine /
|→Ganglion

Question 8

Photoreceptors: lifespan & signal type

Answer 8

Lifespan:
12 days
phagocytosed by RPE

Signal:
GRADED membrane potential, no AP
regulated by gated cGMP chanels

Question 9

RODS vs CONES

Answer 9

RODS:
- dark
-scotopic
-1 kind
- bit slower than cones

CONES:
- Light (color and high res.)
- Photopic
- 3 kinds
- Bit faster than rods

Question 10

Dark vs Light

Answer 10

DARK
-cGMP channels open let Na+ & Ca2+ in
- K+ out
- depolarization
-release glutamate

LIGHT:
- Na+ & Ca2+ channel close
- hyperpolarization
- less glutamate

Question 11

Phototransduction cascade & stopping

Answer 11

Photons turns retinal form II-cis to all-trans config. → activated transducin → activate phosphodiesterase → hydrolyze cGMP (*5’ GMP) → lower cGMP → channels close → HYPERPOLARIZATION

Stopping: activated rhodopsin kinose: allow arrestin to bind and stop

Question 12

Phototransduction cascade amplification

Answer 12

↓ I rhodopsin
↓ ~800transducin
↓ ~800PDC
↓ ~ 4800 hydrolyzed cGMP
↓ ~200 cGMP channels close
↓ 1mv hyperpolarization

Question 13

Where is transducin bound ? (active + inactive)

Answer 13

Active: GTP
Inactive: GDP

Question 14

Retinoid cycle

Answer 14

active retinal + opsin -> (ADD PHOTON) all-trans retinal dissociates from opsin -> all trans retinal converted to all-trans retinol -> shuttled to RPE via IRBP -> all trans retinol converted to 11-cis retinal -> shuttled back -> (ADD OPSIN) start over!

Question 15

Cone & rod types (colorblindness)

Answer 15

Short (blue), medium (green) & long (red) cones
Only one kind of rod

Color blind ppl are missing a cone type
Achrotopsia: No CONES