phototransduction and retinal processing

Question 1

excitatory NT in the retina?

Answer 1

glutamate

Question 2

5 classes of neurons in retina?

Answer 2

! Photoreceptor cells ! Bipolar cells
! Horizontal cells
! Amacrine cells
! Ganglion cells

Question 3

are there more rods or cones?

Answer 3

20 more rods

Question 4

do photoreceptors divide?

Answer 4

no, but they produce more disks (layers) with photopigment

Question 5

which are more sensitive rods or cones?

Answer 5

rods, have more pigment

Question 6

which has more convergence rods or cones?

Answer 6

rods

Question 7

which amplify more rods or cones?

Answer 7

rods

Question 8

which mediate night vision rods or cones?

Answer 8

rods

Question 9

which mediate day vision rods or cones?

Answer 9

cones

Question 10

which respond faster rods or cones?

Answer 10

cones

Question 11

which do color rods or cones?

Answer 11

cones

Question 12

which have higher acuity rods or cones?

Answer 12

cones

Question 13

which requires the most light to be activated rods or cones?

Answer 13

cones, rods can react to a single photon of light

Question 14

what ion channels are in the outer layer of photoreceptors?

Answer 14

Na and some Ca

Question 15

what keeps the channels open constitutively?

Answer 15

cGMP

Question 16

why are channels kept open constitutively?

Answer 16

maintains slight depolarization, -40mV

Question 17

does light cause an increase or decrease in NT release?

Answer 17

decrease

Question 18

is cGMP higher in light or dark?

Answer 18

in dark, “dark current”, opens Ca2+ channels constitutively at low levels

Question 19

steps of phototransduction activation

Answer 19

rhodopsin —> transducin —> phosphodiesterase —> [cGMP] drops —> hyperpolarization

Question 20

steps of termination

Answer 20

• rhodopsin kinase phosphorylates rhodopsin so it now interacts with arrestin
• reduced [cGMP] allows the rhodopsin kinase activity
• opsin separates from retinal and all trans retinal returns to cis

Question 21

what does retinal do?

Answer 21

• binds to opsin to form rhodopsin

- turns from cis to trans in presence of photons

Question 22

what determines the optimal wavelength for a given visual pigment?

Answer 22

type of opsin, retinal is always the same

Question 23

match colors with their optimal wavelengths

Answer 23

blue 420nm
green 531nm
red 558nm

Question 24

which chromosome encodes rod opsin?

Answer 24

3

Question 25

which chromosome encodes blue opsin?

Answer 25

7

Question 26

which chromosome encodes green/red opsin?

Answer 26

X chromosome

Question 27

what are the output cells of the retina?

Answer 27

gangion cells

Question 28

three types of ganglion cells:

Answer 28

1) on-center - light in center activates 2) off-center - light in surround activates 3) W type - overall reactive - most sensitive to blue light

Question 29

which have larger receptive fields M or P types?

Answer 29

M

Question 30

which sense movement M or P?

Answer 30

M

Question 31

which sense color M or P?

Answer 31

P

Question 32

which type of ganglion cells project to the hypothalamus?

Answer 32

W type

Question 33

what area of the brain is involved in pupillary reflexes?

Answer 33

pretectal area of midbrain

Question 34

what's the difference between a direct and consensual pupillary response?

Answer 34

direct is ipsilateral and consensual is contralateral

Question 35

Edinger-Westphal nucleus?

Answer 35

receives info from both eyes and projects to ciliary ganglion along CN III to smooth muscle of pupillary sphincter

Question 36

what does the superior colliculus do?

Answer 36

- head and eye movements toward visual stimulus | - coordination of visual, auditory, somatic info

Question 37

what part of the brain receives most retinal projections?

Answer 37

lateral geniculate nucleus of thalamus

Question 38

which types of ganglion cells project to the lateral geniculate nucleus of the thalamus?

Answer 38

M and P

Question 39

how is the lateral geniculate nucleus of the thalamus layered?

Answer 39

4 outer layers from parvocellular (P type) cells | 2 inner layers from magnocellular (M type) cells