Eyes 4

Question 1

duplicity theory

Answer 1

our eyes adjust to seeing in the daytime (Photopic vision) and at nighttime (Scotopic vision). At a mid range of luminance, both rods and cones are working (Mesopic vision)

Question 2

dark adaptation

Answer 2

First move into the dark:
Cones not working – not enough light
Rods not working – Rhodopsin was bleached and cannot be used right away
Move from a well lit area into a dark area.

Question 3

why ships red lights

Answer 3

Rods are blind to Red light, red wavelength is not captured by rhodopsin, therefore will not bleach them. Use cones to detect red light

Question 4

light adaptation

Answer 4

All Cones and Rods instantaneously stimulated and photopigments are bleached, causes flood of signals to the brain and is seen as a bright glare and you can’t see.
After only few seconds to 60 sec, cones desensitize and adapt (reset time before can fire again) and you can see again. Cones are faster to recover from bleaching than rods. Cones also require more energy to become bleached.
Rods unable to function because Rhodopsin is bleached

Question 5

Young-Helmholtz Trichromacy Theory of color vision -

Answer 5

brain assigns color based on the proportion of nerve impulses from each cone type: blue, green, and red cones.

Question 6

opponent process theory

Answer 6

After cones, ganglion cells send signals to the brain in three types of opposing color channels (Blue+Yellow, Red+Green, and Black+White)

Question 7

Final stage to color perception occurs at the

Answer 7

cerebral cortex

Question 8

dichromats

Answer 8

(2% of men) one of the three cones pigments is missing so color is reduced in two dimensions red- green colors or blue-yellow. Red-Green most common.

Question 9

(Protanopia) –

Answer 9

no red cones, so red appears grey

Question 10

deuteranopia

Answer 10

(Deuteranopia) – no green cones.

Red and Green pigment genes are on the X-chromosome, mutations more common in males than females.

Question 11

(Tritanopia) –

Answer 11

no blue cones, blues appear greenish, yellows and oranges appear pinkish, and purple color appears deep red. Blue pigment gene is on chromosome 7, so equal in males and females (rare).

Question 12

Anomalous trichromats

Answer 12

(6% of men) – one of the three cone pigments is altered in its spectral sensitivity, not missing so poor red-green hue discrimination.

Question 13

Monochromats

Answer 13

(0.001% of population) – two cones or all three cones not functional – no color vision at all, see only black, white, and greys

Question 14

Information about where light is, what’s moving, where borders are, etc. processed by

Answer 14

retina, sent through optic nerve

Hits LGN (Lateral Geniculate Nucleus) in the thalamus, then relayed to Primary Visual Cortex (V1) in the Occipital lobe

Question 15

phototransduction in rods

Answer 15

Analogous to activity at G-protein coupled neurotransmitter receptor - but causes a decrease in second messenger
Light energy changes shape of pigment molecule in membrane
Shape change activates G-protein, which reduces production of second messenger
Na+ channels closed

Question 16

dark current

Answer 16

Rod outer segments are depolarized in the dark because of steady influx of Na+
Photoreceptors hyperpolarize in response to light

Question 17

phototransduction

Answer 17

Rod pigment rhodopsin absorbs light, changes shape
G-protein (transducin) stimulated
Turns on enzyme phosphodiesterase (PDE), which breaks down cGMP
Reduction of cGMP causes Na+ channels to close, membrane hyperpolarizes (Na+ stuck outside)

Question 18

signal amplification

Answer 18

each pigment activates many g-proteins, each g-protein activates many proteins, etc. (we can detect a single photon because of this!)

Question 19

dark adaptation factors

Answer 19

Dilation of pupils

Regeneration of unbleached rhodopsin (going into dark)

Question 20

light adaptation

Answer 20

temporarily saturated upon entering bright light from dark

Cones hyperpolarized immediately, but membrane will gradually depolarize to -35mV thanks to Ca2+