Exam 2-Vision

Question 1

rhodopsin

Answer 1

retinal + opsin

pigment (absorbs light)

Question 2

retinal

Answer 2

• derived from vitamin A
• as it becomes trans moves away from opsin (bleaching occurs)
• cis: low energy form (fits within opsin)

Question 3

opsin

Answer 3

transmembrane protein; g protein linked (transducin)

Question 4

photoreceptors

Answer 4

rods: low light conditions (mostly free folding disks)
cones: light and color (stacks of membranes allowing for more rhodopsin)

Question 5

photoreceptors in dark

Answer 5

• lots of Na channels open in the dark (less negative -depolarize)
• cGMP: binds to keep channels open
• K efflux, Na influx (depolarization)

Question 6

photoreceptors in light

Answer 6

1. retinal becomes trans and shape of rhodopsin changes
2. transduction (G protein) activates enzyme
   cGMP phophodiesterase
3. making cGMP n longer cyclic (which was opening Na channels)
4. Na channel closes (hyperpolarize and stop releasing neurotransmitter which is normally released when not active-inhibitory)

Question 7

cones

Answer 7

3 (red, blue, green)

-opsin excited at different wavelengths (sensitive to different band of wavelengths)

Question 8

rods

Answer 8

“wimpy” version of opsin (lower threshold)

Question 9

eye anatomy

Answer 9

cornea, pupil, iris, ciliary muscle, lens, vitreous humor, retina, blind spot, fovea, optic nerve

Question 10

retina

Answer 10

• photoreceptors
• all rhodopsin at furthest point in back of eye (closest to blood supply
• ganglion cells: blocks light (blind spot-brain corrects for this)
• multiple cones to one bipolar cell; only one rod to a bipolar cell

Question 11

visual activity

Answer 11

rods: convergent info, increased sensitivity: decreased acuity
cones: decreased sensitivity: increased acuity

Question 12

cornea

Answer 12

bent surface (refracts light into small hole)
does most of the refracting

Question 13

lens

Answer 13

bends light for focus (slight bending)

always convex

Question 14

physics and focusing

Answer 14

• close up light (more of an angle; more refraction; more round)
• further away objects (less angle; less refraction; less round)

Question 15

ciliary muscle

Answer 15

• elastic (stretch and return to original position)
• ciliary muscle: keeps lens from being completely round
• ciliary zonule: suspensory ligaments (connect muscle to lens)

Question 16

(ciliary muscle)

active/passive focusing

Answer 16

ACTIVE: contract rounded muscle (smaller circle); decrease tension on ligaments; decrease pull on lens, bending more light
PASSIVE: relax rounded muscle (bigger circle); increase tension on ligaments; less rounded lens, bending less light

Question 17

abnormalities

Answer 17

• presbyopia: decrease lens elasticity, near point of vision increases
• myopia: nearsighted; eyeball too long
• hyperopia: farsighted; eyeball too short