Retinal Physiology

Question 1

what do photoreceptors do in transduction?

Answer 1

photoreceptors convert light into a neuroelectrical response (act as a transducer)

Question 2

what does a photoreceptor do when it is excited?

Answer 2

hyperpolarize

Question 3

unlike typical neural cells, photoreceptors do not produce:

Answer 3

action potentials

Question 4

for transduction, what occurs in the dark?

Answer 4

the Na+ channels are open and Na+ flows into the outer segment and is pumped out of the inner segment (continuous cycle)

Question 5

what is the result of light on the transduction process?

Answer 5

Na+ channels close so Na+ doesn’t flow in but it is still pumped out (hyperpolarizes)

Question 6

what is the type of neurotransmitter release that occurs in dark current transduction

Answer 6

photoreceptors release neurotransmitters continually in the dark

Question 7

in the dark, the inside of the photoreceptor is about _____ more ____ than the outside

Answer 7

20mV more negative

Question 8

when light hits the photoreceptor there is a series of chemical reactions that results in the inside of the cell becoming more ____, about ___ mV

Answer 8

more negative, about -60 mV

Question 9

effects of light: rhodopsin will be converted to ->

Answer 9

opsin + all-trans retinal

Question 10

effects of light: concentration of free cGMP _____

Answer 10

decreases

Question 11

effects of light: decreasing the cGMP concentration results in ____ of Na+ channels

Answer 11

closes some of the

Question 12

what is cGMP needed for?

Answer 12

needed to bind at Na+ channels to keep them open

Question 13

effects of light: results in the inside of the cell becoming more ____ (+ or -)

Answer 13

negative

Question 14

what retinal cells are capable of action potentials?

Answer 14

amacrine cells and ganglion cells

Question 15

what cells are only capable of producing membrane potential changes (but NOT action potentials)?

Answer 15

photoreceptors, horizontal cells, bipolar cells

Question 16

___ pathway causes photoreceptors to hypoerpolarize in response to light

Answer 16

ON

Question 17

ON ganglion cell synapse is in:

Answer 17

IPL sublamina B

Question 18

OFF ganglion cell synapse is in:

Answer 18

IPL sublamina A

Question 19

horizontal cells can ____ adjacent bipolar cells

Answer 19

inhibit

Question 20

what is the pathway for lateral information flow? (lateral inhibition)

Answer 20

light stimulates a single photoreceptor -> stimulates bipolar cell -> stimulates ganglion cell (ON pathway)

Question 21

what are the three types of ganglion cells based on receptive field properties (cat)?

Answer 21

• X cells
• Y cells
• W cells

Question 22

what ganglion cell type (cat): beta cells and responds as long as light is on?

Answer 22

X cells

Question 23

what ganglion cell type (cat): alpha cells and responds when light is turned on or off?

Answer 23

Y cells

Question 24

what ganglion cell type (cat): gamma cells?

Answer 24

W cells

Question 25

X and Y cells make up ___% of the cells and project to ____

Answer 25

80%, project to LGN

Question 26

W cells make up ___% of the cells and project to the ____

Answer 26

20%, project to the superior colliculus

Question 27

___ cells show linear spatial summation

Answer 27

X cells

Question 28

___ cells show nonlinear spatial summation

Answer 28

Y cells

Question 29

__ cells demonstrate a null point with counterpoising gratings

Answer 29

X cells

Question 30

__ cells demonstrate a doubling of their responses

Answer 30

Y cells

Question 31

in the sine wave grating, what is the most sensitive area?

Answer 31

the peak- midrange about 3-5 cycles/degree

Question 32

20/20 on a snellen chart is about ___ cycles/degree on contrast sensitivity function

Answer 32

30

Question 33

how are receptive field center and eccentricity related?

Answer 33

an increase in the receptive field center as the eccentricity is increased

Question 34

function of X cells

Answer 34

involved with pattern and spatial vision | detection of very fine, small objects

Question 35

function of Y cells

Answer 35

involved in movement or temporal vision

Question 36

types of ganglion cells found in the primates

Answer 36

P alpha (P cells) and P beta (M cells)

Question 37

P cells (P alpha cells) project to ____ layers of LGN

Answer 37

parvocellular

Question 38

M cells (P beta cells) project to the ____ layers of LGN

Answer 38

magnocellular

Question 39

P cells are ___% of the ganglion cells

Answer 39

80%

Question 40

___ cells are wavelength specific (color sensitive)

Answer 40

P cells | P beta

Question 41

spatial summation type of P cells (P beta)

Answer 41

linear

Question 42

P cells are similar to ___ cells

Answer 42

X cells

Question 43

___ cells (P/M) have large cell body

Answer 43

M cells

Question 44

M cells make up ___ % of the ganglion cells

Answer 44

10%

Question 45

are M cells wavelength specific?

Answer 45

no

Question 46

spatial summation for M cells is

Answer 46

both linear and nonlinear

Question 47

how many layers in the LGN?

Answer 47

6