Exam 2 Vision 2

Question 1

What is the visual acuity of rod vs cone cells

Answer 1

Visual acuity in rods cells are: low in cones cells are high

Question 2

What is the color detection of rod cells vs cone sells?

Answer 2

Rod cells: black and white

Cone cells: Color

Question 3

What is the response time in rod cells vs cone cells?

Answer 3

Rod cells: slow

Cone cells: fast

Question 4

What is the sensitivity to light in rod cells vs cone cells?

Answer 4

Rod cells: high (scotopic vision or night vision)

Cone cells: Low (photopic vision or daylight vision)

Question 5

What is the convergence of rod cells vs cone cells?

Answer 5

Rod cells: high

-because you’re requiring signals from several rod cells into one bipolar cells

Cone cells: low

-one cone cell per bipolar cell

Question 6

What is the numbers in rod cells vs cone cells?

Answer 6

Rod cells: many rods (20 rods for every cone cell)

Cone Cell: very few

Question 7

What is the photopigment in rod vs cone cells?

Answer 7

Rod: rhodopsin

Cone: Red, Green, or Blue opsin

Question 8

What is this called?

• In complete darkness, the membrane potential of the outer segment is depolarized.
• There are high intracellular levels of cyclic guanosine monophosphate (cGMP, second messanger)
• Na+ continually influxes through cyclic-GMP gated channels.

There is a delayed-rectifier K + current and a Na + -K+, Ca2+ exchanger at work

Answer 8

The dark current

Question 9

Explain Rod Phototransduction

Answer 9

• The levels of cGMP decrease
• The ion channels close.
• Membrane becomes hyperpolarized.
• There is less calcium in the cell.
• There is less release of neurotransmitter.

Question 10

Rod Phototransduction:

• Photopigment (rhodopsin) in the membrane of rod outer segments ______ electromagnetic radiation in the form of ____.
• Rhodopsin is a receptor _____ (opsin) with a prebound chemical agonist (retinal).
• Absorption of light causes a change in the atomic conformation of retinal which leads to the activation of _____ (bleaching).
• Bleaching of rhodopsin stimulates a _______, transducin.
• This activates the effector enzyme, ___________.
• This leads to the breakdown of _______.
• Cyclic nucleotide-gated (CNG) channels _______.
• The membrane becomes more _________.
• Photoreceptors hyperpolarize in response to _______.

Answer 10

1) absorbs, light
2) Protein
3) opsin
4) G-protein
5) phosphodiesterase (PDE)
6) cGMP
7) close
8) negative (hyperpolarizes)
9) light

Question 11

What is the purpose of the retinoid cycle?

•Retinal converts back to its cis configuration using arrestin, rhodopsin kinase, and GTP.

–This is done in the RPE

• Transducin reassembles, GDP remains bound.
• Phosphodiesterase is inactivated.
• Guanylate cyclase makes more cGMP.
• CNG channels re-open.
• Sodium is able to flow into the cell, depolarizing it again.

Answer 11

Returing rod phototransduction to resting state

Question 12

•Phototransduction in cones is the same as in rods except for the ________________________.

Answer 12

type of opsin in the outer segments

Question 13

Describe differences in P and M type ganglion cells

Answer 13

P is for parvo and means small

M is for magno and means large

Question 14

These cells generate axons that travel through the optic nerve to the brain

-these are third order neurons

Answer 14

Ganglion cells

Question 15

•The ________________ of a cell in the visual system is the area of retina that, when stimulated by light, changes the cell’s membrane potential.

Answer 15

Receptive field

(a) Ganglion cell receptive fields have center-surround organization.
(b) An OFF-center ganglion cell responds with many action potentials when a dark spot (shadow) is imaged on its receptive field center.
(c) If the spot is enlarged to include the receptive field surround, the response is greatly reduced.

Question 16

_____________ are mainly responsive to differences in illumination that occur within their receptive fields.

Answer 16

Ganglion cells

Question 17

What is Young-Helmholtz trichromacy theory

Answer 17

• any color can be created by a combination of three primary colors.

Question 18

How can context change the appearance of color?

Answer 18

When you change the background you see a different color because of the contrast

Question 19

Trichromats

1) Normal

•Can distinguish about 150 hues

2) Protanomalous

• Reduced ______ sensitivity
• Can distinguish only 5 to 25 hues

3) Deuteranomalous

• Reduced _____ sensitivity
• Can distinguish only 5 to 25 hues

Answer 19

1) red
2) green

Question 20

Dichromats

1) Protanopes

•No _____ sensitivity (red looks black to them)

2) Deuteranopes

•No _____ sensitivity

3) Tritanopes

•Rare individual who are insensitive to ____ wavelengths of light.

Answer 20

1) Red
2) Green
3) short

Question 21

Monochromats

–Totally color blind

–The world is seen as shades of ______.

Answer 21

1) gray