Ocular: Phototransduction

Question 1

What is photoreception?

Answer 1

Light detection that lead to vision and depends on photoreceptors

Question 2

What is scoptopic vision?

Answer 2

Dim light and motion detection

Question 3

What is photopic vision?

Answer 3

Color and detail

Question 4

Rods are apart of which type of vision?

Answer 4

Scoptopic vision

Question 5

Rods are good for..

Answer 5

Dim illumination, very sensitive

Question 6

Cones are apart of which type of vision?

Answer 6

Photopic vision

Question 7

Cones are for..

Answer 7

-specialized for color and detail
-less sensitive to motion detection

Question 8

Where do the rods reach peak density?

Answer 8

-18% away from fovea
-4.5 mm outside the fovea

Question 9

Where do cones reach their peak density?

Answer 9

Fovea
-blind spot

Question 10

How many rods are there?

Answer 10

92-120 million rods

Question 11

Peak absorption of rods?

Answer 11

500-510 nm

Question 12

Many rods gather information onto ___ rod bipolar cell

Answer 12

One

Question 13

The convergence of the rods to one bipolar cell increases…

Answer 13

Sensitivity

Question 14

How many cones are there?

Answer 14

5-6 million

Question 15

The cone photopigments are stored in the

Answer 15

Disc membrane

Question 16

What are the 3 photopigments that cones could have?

Answer 16

S cones
M cones
L cones

Question 17

S cones are sensitive to what wavelength?

Answer 17

420 nm

Question 18

What wavelength are M cones sensitive to?

Answer 18

531-534 nm

Question 19

What wavelengths are L cones sensitive to?

Answer 19

564-588 nm

Question 20

Is there convergence of cones to one bipolar cell?

Answer 20

NOPE

Question 21

What is the peak absorption spectral sensitivity of rod photoreceptors?

Answer 21

498-510 nm

Question 22

What is the photopigments of rods?

Answer 22

Rhodopsin

Question 23

What is the photopigment used by cones?

Answer 23

Conopsin

Question 24

Rhodopsin = _____+ ________

Answer 24

Opsin + 11-cis-retinal

Question 25

Iodopsins= ______ + ________

Answer 25

Photopsin+ 11-cis-retinal

Question 26

What is phototransduction?

Answer 26

Is the series of biochemical events that lead from photo capture by a photoreceptor cell Is the transformation of light into electrical and chemical signals that produces the perception of light

Question 27

What do Cyclic-GMP-Gated(CNG) Cation channels do?

Answer 27

-Allow Na+ and K+ and Ca2+ to enter the cell -causes the cells to be partially depolarized

Question 28

What is the resting membrane potential of the rod photoreceptors in the dark?

Answer 28

-50mV

Question 29

During the dark current in what state are the rod photoreceptors?

Answer 29

Partially depolarized

Question 30

Describe the movement of cations during dark current.

Answer 30

-net flux of cations during flow out of the inner segment -net flux of cations flow into the outer segment plasma membrane

Question 31

What does the flux of cations cause during dark current?

Answer 31

The opening of CNG on the outersegment so they can enter

Question 32

The opening of the CNG it’s important because?

Answer 32

It keeps the dark current and the rods partially depolarized by keeping the Na+ channels open in the dark

Question 33

Are CNG channels of photoreceptors open or closed in the dark?

Answer 33

OPEN

Question 34

Are CNG channels of photoreceptors are open or closed in light?

Answer 34

Closed

Question 35

Is glutamate release by photoreceptors higher or lower in the dark?

Answer 35

higher

Question 36

Is glutamate release by photoreceptors higher or lower in the light?

Answer 36

Lower

Question 37

What happens to 11-cis-retinal when rhodopsin is photoisomerized?

Answer 37

It becomes all-trans retinol

Question 38

The classical visual cycle involves the cycling of ________ between the rod outer segments and RPE.

Answer 38

11-cis-retinal

Question 39

Where does the reduction of all-trans-retinol occur?

Answer 39

Outer segments of photoreceptors

Question 40

Reisomerization of all-transretinol into 11-cis-retinal occurs in the ?

Answer 40

RPE

Question 41

What does transducin stimulate?

Answer 41

cGMP-phosphodiesterase(PDE-6)

Question 42

What does PDE6 do?

Answer 42

Converts cGMP to 5’-GMP

Question 43

How does photoisomerization of rhodopsin change intracellular concentration level of cGMP?

Answer 43

Rhodopsin conformationally changes to metarhodopsin (MII)and stimulates transducin to produce cGMP PDE6

Question 44

Na+ channels are kept open by high concentrations of cGMP and are therefore open or closed in the dark?

Answer 44

Open

Question 45

When light hits, transducin is released and causes what? what happens to Na+ channels?

Answer 45

Transducin changes cGMP to 5’-GMP, so Na+ channels are forced to close

Question 46

What is electronic spread?

Answer 46

In the dark, Na+ is flowing from OS to IS which causes continual depolarization of the membrane and release of neurotransmitters

Question 47

Why does glutamate release form photoreceptors decrease when stimulated by light/

Answer 47

When the photoreceptors hyperpolarizes in response to light, it stops releasing glutamate