Hirsch - Eye

Question 1

Surface features of the eye

Answer 1

Sclera - Iris - Pupil

Question 2

Eyeball

Answer 2

Cornea & Sclera
Aqueous humor in anterior chamber
Ciliary muscle & choroid
Retina
Iris & Pupil
Ciliary muscle & Zonule fibers & Lens
Vitreous humor (jelly-like)
Fovea
Optic disk

Question 3

Choroid

Answer 3

nourish neural part of eyeball; rods and cons

Question 4

Focal planes with respect to the retina

Answer 4

Emmetropia
Myopia - nearsighted
Hyperopia - far sighted

Question 5

ciliary muscle contract, springs (zonule fibers) …. the lens ….

Answer 5

when ciliary muscle contract,
zonule fibers become loose
lens focuses close object to retina

Question 6

ciliary muscle relax, spring (zonule fibers) …. the lens ….

Answer 6

when ciliary muscle relax,
zonule fibers become tight,
lens focuses distant object to retina

Question 7

myopia or nearsighted when…

Answer 7

eye too long
lens too round
need concave lens

Question 8

hyperopia or far-sighted

Answer 8

eye too short
lens too flat
need convex lens

Question 9

Why are rods and cons far back near choroid?

Answer 9

high metabolic demands

choroid nourishes the cells

Question 10

Basic Retinal Anatomy from proximal to distal

Answer 10

light come in
—- inner limiting membrane
—- nerve fiber layer
ganglion cell layer(ganglion cells)
inner plexiform layer(amacrine cells)
inner nuclear layer (bipolar cells)
outer plaxiform later(horizontal cells)
outer nulear layer (muller cells)
—- outer limiting membrane
photoreceptor layer (rods, cones, pigment epithelium)

Question 11

thickness of retina

Answer 11

thick centrally and thin peripherally

Question 12

the fovea

Answer 12

visual acuity maximized
cones only - smaller dense
 * outer cones largerand less dense
 * outer rods max around fovea and decrease (due to thinner retina)
foveal pit (around: foveal slope)

Question 13

Disease in retina

Answer 13

macular (foveal pit, foveal slope, para & peri fovea) degenration
retinitus pigmentosa
diabetic retinopathy

Question 14

disks in conse ve. rods

Answer 14

cone; outer surface of disks embedded in the cell membrane; faster
rods; disks are stacked inside of cell membrane; slower

Question 15

rod vs. cone

Answer 15

slow vs fast

less light vs more light

Question 16

recording of rod during stimulation of punctate sites with a llaser

Answer 16

no matter where a photon lands, the whole outer segment of rod hyperpolarizes

Question 17

origin of receptor currents

Answer 17

when dark; depolarized; sodium influx

when light; hyperpolarized; sodium block

Question 18

phototransduction cascade under dark and under light

Answer 18

lots of cGMP in cytoplasm keep open Na channels in outer membrane

1. opsin molecule (e.g. rhodopsion in rod, embeded in the disks) switches from 11-cis to all-trans (e.g. metarhodopsin)
2. in all-trans state opsin activates GTP-binding protein - transducin(its alpha subunit binds GTP and activates a phosphodiesterase;PDE)
3. phosphodiesterase (PDE) hydrolyzes cGMP to GMP
4. concentration of cGMP drops. many cGMP fall away from NA channal closing the channel, hyperpolarizing the cell

Question 19

one photon absorbed by one molecule of opsin activates — molecules of dransducin

Answer 19

800 molecules of transducin

Question 20

each molecule of transducin activate —- phosphodiesterase

Answer 20

1 phosphodiesterase (PDE)

Question 21

each molecule of phosphodiesterase hydrolizes

Answer 21

upto 6 molecules of cGMP

Question 22

how does one photon affect sodium channes and membrane potential?

Answer 22

one photon leads to the closure of 200 sodium channels and drop 1mV in membrane potential

Question 23

adaptation

Answer 23

great sensitivity of phototransduction cascade —> early saturation
adaptation extend the dynamic range of response
dependent on Ca (retinal Na Channel also permeable to Ca)
Na channel closure -> Ca decrease -> increased guanylate cyclase activity - increase more cGMP - and rhodopsin kinase activity - phosphorylated metarhodopsin binds arrestin interferes ability of metarhodopsin to activate transducin - (which are inhibited by Ca)

Question 24

decrease in calcium concentration in Rod

Answer 24

increase guanylate cyclase => increase cGMP

increase rhodopsin kinase => phosphorylate metarhodopsin -> bind arrestin which conflicts with transducin

Question 25

sensitivity of rods and cones

Answer 25

blue(cone) - rod - green (cone) - red (cone)

Question 26

Ocular dominance

Answer 26

Perceive depth