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ZOOL 342 > Vision Retina 1 > Flashcards

Vision Retina 1 Flashcards

1
Q

Draw the electromagnetic spectrum.

A

slide 2

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2
Q

What is the wavelength range that is visible to humans?

A

750nm - 350nm

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3
Q

describe the info transmission pathway from the eyes to the brain

A
  1. retina
  2. bipolar cells
  3. ganglion cells (ipRGCs)
  4. LGN
  5. visual cortex
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4
Q

describe the info transmission pathway from the eyes to the brain that drives the circadian rhythm

A
  1. retina
  2. bipolar cells
  3. ganglion cells (ipRGCs)
  4. SCN (suprachiasmatic nucleus)
  5. PVN (paraventricular nucleus) - retinohypothalamic tract
  6. IML (intermediolateral nucleus)
  7. SCG (superior cervical ganglion)
  8. pineal gland - release melatonin
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5
Q

Describe the info transmission pathway from the eyes to the brain that regulates the pupillary reflex.

A
  1. retina
  2. bipolar cells
  3. ipRGCs
  4. IGL (intergeniculate leaflet)
  5. OLN (olivary pretectal nucleus)
  6. EW nucleus
  7. motor neurons in ciliary ganglion (CG) –> control iris muscle
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6
Q

draw the pathways from the eyes to the brain

A

slide 3

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7
Q

What is rhodopsin

A

light-sensitive receptor protein involved in visual phototransduction

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8
Q

What are the different types of eyes? Describe them.

A
  • compound eyes: composed of numerous identically repeated visual units, the ommatidia
  • camera type eyes: lens, retina, photoreceptor cells, afferent neurons (SINGLE UNIT)
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9
Q

classify the following as having compound or camera type eyes: snail, ark clam, scallop, fly, vertebrate, cephalopod

A
  • compound eyes: ark clam, fly
  • camera type eyes: snail, scallop, vertebrate, cephalopod
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10
Q

What are the 2 parts of rhodopsin? Define them.

A
  • opsin = protein with 7 trans-membrane alpha helices
  • retinal = chromophore (absorbs light); vitamin A derivative
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11
Q

What is a chromophore? example?

A
  • protein that absorbs light
  • retinal
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12
Q

TRUE or FALSE: retinal is a vitamin B derivative

A

FALSE: vitamin A

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13
Q

TRUE or FALSE: in vertebrates, 11-cis-retinal is attached to the 7th transmembrane domain

A

TRUE

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14
Q

how is activated rhodopsin form? What is it called once activated? What does it start as? What results after?

A
  • 11-cis-retinal converted by LIGHT to ALL-TRANS RETINAL
  • conformation change in the OPSIN to produce activated rhodopsin –> METARHODOPSIN II
  • G protein cascade results
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15
Q

label the structures of the vertebrate eye

A

slide 7

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16
Q

function of the ciliary body

A

contraction –> lens fattens –> focus near objects

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17
Q

function of fovea

A

photoreceptors most densely packed here

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18
Q

where are there no photoreceptors in the eyeball?

A

optic disk (where optic nerve is attached)

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19
Q

arrange the order from front to back, structurally and in order of info transmission: photoreceptors, ganglion cells, bipolar cells

A
  • structural: ganglion cells –> bipolar cells –> photoreceptors
  • info: photoreceptors –> bipolar cells –> ganglion cells
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20
Q

what kind of connections do horizontal and amacrine cells make in the retina?

A

lateral

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21
Q

between which cell layers are horizontal cells located in the retina? amacrine?

A
  • horizontal cell = between photoreceptors and bipolar cells
  • amacrine cell = between bipolar cells and ganglion cells
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22
Q

which scientist first visualized the human rod and cone?

A

ramon y cajal

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23
Q

draw a rod and a cone and label the structures:
- disc
- outer segment
- inner segment
- synaptic ending
- nucleus
- axon
- mitochondria
- connecting cilium

A

slide 11

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24
Q

Which structure of the photoreceptor is rhodopsin found in?

A

disc

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25
Q

define the structural difference between rods and cones

A
  • rods: pigment rhodopsin (black dots) is embedded in membranes arranged in the form of disks, which are NOT continuous with the outer membrane of the cell
  • cones: the pigment molecules are on infolded membranes that are CONTINUOUS with the surface membrane

hint: CONes = CONtinuous

26
Q

TRUE or FALSE: light depolarizes vertebrate photoreceptors

A

FALSE: hyperpolarizes

27
Q

describe the mechanism by which light hyperpolarizes photoreceptors (draw)

A
  1. light is absorbed, rhodopsin is activated
  2. the G protein TRANSDUCIN is stimulated; GTP exchanged from GDP on alpha subunit
  3. alpha-subunit separates and activates cGMP phosphodiesterase; breakdown cGMP to 5’-GMP
  4. as cGMP decreases, cGM detaches from cation channels, channels CLOSE; less Na+ enters the cell and the cell HYPERPOLARIZES

slide 14

28
Q

What is meant by “G protein coupled processes are amplifiers”, in terms of photoreceptors and light?

A

G protein processes make photoreceptors extremely SENSITIVE TO LIGHT

29
Q

What are the 2 main steps of amplification in photoreceptors?

A
  1. each transducin can activate at least 12-14 molecules of cGMP-phosphodiesterase
  2. each cGMP phosphodiesterase hydrolyzes 100,000s of cGMP
30
Q

What is the end result of the amplification in photoreceptors in response to light?

A

single activated rhodopsin closes 100s or ion channels, preventing influx of one million Na+ ions

31
Q

Single photon leads to a ______ pA (reduction/increase?) in current.

What does this mean

A

0.5 pA reduction; very sensitive to light bc of GPCR cascade

32
Q

Draw the current resulting from single photos, flases of increasing intensity, and steady illumination.

A

slide16

33
Q

TRUE or FALSE: vertebrate photoreceptors are active in the light

A

FALSE: active in the dark

34
Q

TRUE or FALSE: cyclic nucleotide gated channels normally OPEN in the dark

A

TRUE

35
Q

Describe the steps in a dark current of a photoreceptor

A
  1. cGMP-gated Na+ channels OPEN IN THE DARK
  2. inflow of Na+ (dark current)
  3. membrane potential depolarized -30 mV
  4. GLUTAMATE released at synaptic terminals INHIBITS bipolar cells
36
Q

Describe the steps in the light (current) of a photoreceptor.

A
  1. under LIGHT< isomerization of retinal activates enzyme that breaks down cGMP
  2. cGMP-gated Na+ channels CLOSE IN THE LIGHT
  3. inflow of Na+ SLOWS
  4. membrane potential HYPERPOLARIZED
  5. GLUTAMATE release turned OFF, which EXCITES bipolar cells
37
Q

TRUE or FALSE: photoreceptors produce APs in their axons

A

FALSE: not AP; produce GRADED POTENTIALS because axons are short

38
Q

by how much can a single photon hyperpolarize membrane potential

A

1mV

39
Q

Draw a diagram of the membrane potential of the photoreceptor in dim, dark, and bright.

(hint: graded potentials)

A

slide 17

40
Q

TRUE or FALSE: light depolarizes vertebrate photoreceptors and hyperpolarizes invertebrate photoreceptors

A

FALSE: hyperpolarize vertebrate, depolarize invertebrate

41
Q

Draw the membrane potential in response to light in invertebrate photoreceptors vs vertebrates.

A

slide 18

42
Q

Draw photoreceptors in insects vs vertebrates. Compare with ancestral neuroepithelial cell.

A

slide 19

43
Q

Compound eyes are composed of an array of _______________.

A

ommatidia

44
Q

What are the cells that make up an ommatidium? How are they arranged? How many in drosophila?

A
  • retinular cells
  • arranged in circle
  • 8 in drosophila (per ommatidium)
45
Q

What forms the lens of an ommatidium?

A

cornea overlying a crystalline cone

46
Q

What do the microvilli on the rhabdomere of an ommatidium conatin?

A

rhodopsin, G proteins, cation channels

47
Q

Draw the structure of ommatidia; label.

A

slide 20

48
Q

Describe the steps of transduction in rhabdomeric photoreceptors. Draw.

A
  1. activated rhodopsin activates a G protein (NOT TRANSDUCIN); GTP exchanged for GDP on an a-subunit
  2. a-subunit separates and activates PLC
  3. PLC catalyzes: PIP2 –> IP3 and DAG
  4. causes the opening of transient receptor potential (TRP) channel
  5. Na+ (and Ca2+) enter cell; DEPOLARIZATION; scaffolding protein speeds up the process

slide 21

49
Q

What is pigment bleaching?

A

when retinal is converted to all-trans isomer, it separates from the opsin

50
Q

What is pigment regeneration?

A

opsin is transported to pigment epithelium where it is converted BACK TO 11-cis retinal, then transported back to photoreceptors

51
Q

How long does pigment regeneration take?

A

30+ minutes

52
Q

draw a diagram to show chromophore bleaching and recylcing. Label the rate limiting step

A

RLS = all-trans retinal –> 11-cis retinal + OPSIN (dark adaptation)

slide 23

53
Q

What is another name for pigment regeneration?

A

dark adaptation

54
Q

What is the key ion in light adaptation?

A

Ca2+

55
Q

How do intracellular levels of Ca2+ affect light adaptation? light vs dark

A
  • in dark, Ca2+ continuously flowing into cell though open cation channels, but removed by pumps
  • in light, cation channels closed, LESS Ca2+ enter, but still removed by pumps

summary: DECREASE in intracellular Ca2+ leads to light adaptation

56
Q

TRUE or FALSE: metarhodopsin II needs to be activated for light adaptation

A

FALSE: inhibited

57
Q

fall in intracellular calcium leads to 4 processes that contribute to light adaptation. what are these 4 processes?

A
  1. speeds metarhodopsin II shutoff via RECOVERIN
  2. lowers gain of PDE activation
  3. activates cyclase
  4. increase channel affinity for cGMP via CALMODULIN

i.e. prevent hyperpolarization

58
Q

Why must metarhodopsin II be shut off in light adaptation?

A

if not stopped, it will continue to activate transducins, leading to hyperpolarization and closing of channels

59
Q

recoverin in the dark vs in the light

A
  • dark: Ca2+ bound recoverin inhibits PHOSPHORYLATION that shuts off metarhodopsin II
  • light: recoverin can’t inhibit phosphorylation step; metarhodopsin shut off at greater rate; cation channels open

note: Ca2+ binds in the dark because lots of Ca2+ influx in the dark

60
Q

TRUE or FALSE: phosphorylation activates metarhodopsin II

A

FALSE: inactivates

61
Q

TRUE or FALSE: without that phosphorylation site, cation channels stay open for longer because metarhodopsin II is not being inactivated

A

FALSE: channels stay CLOSED for longer bc metarhodopsin II activates transducin, leading to hyperpolarization

62
Q

How does cyclase affect the transduction mechansim in a photoreceptor? What process does it play a role in?

A

converts 5’-GMP back to cGMP; light adaptation

ZOOL 342 (21 decks)

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