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bil 360 > 11c photoreception > Flashcards

11c photoreception Flashcards

1
Q

photoreception

A

a sensory cell’s response to light

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2
Q

three functions of the simplest type of eye

A

photoreception

shading by dark pigment to allow detection of light direction

connection to motor structures to allow phototaxis

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3
Q

define phototaxis and what a pos or neg phototaxis would mean

A

the bodily movement of a motile organism in response to light, either toward the source of light ( positive phototaxis ) or away from it ( negative phototaxis ).

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4
Q

visible spectrum

A

Electromagnetic waves falling in the range that can stimulate an animal’s photoreceptors comprise that animal’s

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5
Q

why does the visible spectrum vary between animal species?

A

bc it depends on the spectral sensitivities of their photoreceptors

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6
Q

visible spectrum range

A

390nm - 720nm, on average.

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7
Q

pigment spot

A

simplest type of eye

adaptive for a facultative autotroph
allowed simple organisms to find light and dark with the help of the flagelllum

found in some protists (e.g., Euglena, Chlamydomonas)

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8
Q

pigment cup

A

allows detection of light stimulus direction

in comparison to the pigment spot, it has more nerve fibers and the pigment cells are bended

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9
Q

optic cup

A

encloses a water filled cavity (pinhole opening)

reduces light scatter
increases resolution
found in many flatworms, rotifers, polychaetes, gastropods, chitons, and echinoderms

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10
Q

deeper cup with a clear epithelial covering

A

further increases resolution

eye is protected from environmental toxins, pathogens

has a photoreceptor layer that will create the future retina

found in Chambered Nautilus (VERY SIMPLE CEPHALOPODS)

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11
Q

eye with primitive lens

A 
eye is able to focus incoming light 
eye can form clearer images 
has a now formed retina
has refractive lens
found in lampreys, fossil hagfishes
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12
Q

complex eye aka camera eye

A

high resolution

has lens and a cornea

ability to form clear images
additional anatomical adaptations for color vision, etc.

compound eye found in insects and some crustaceans

camera eye found in all craniate vertebrates and cephalopod mollusks like an octupus

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13
Q

spot vs cup

A

the cup has less of an opening which increases resolution and reduces distortion
and allows only a certain amount of light to come in

based on video… the cup also helps to avoid predators

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14
Q

lens helps by

A

changing the curvature to adapt to n ear and far vision

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15
Q

why do slow moving or sessile creatures have poor eyesight?

A

it is more dangerous to move so fast when practically blind so you might as well stay in place to protect yourself to avoid bumping into things

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16
Q

eyesight of slow moving or sessile creatures

A

simple eyes detect shadows and close movement

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17
Q

eye sight of slow mobile

A

eyes that aid in navigation, simple image formation

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18
Q

sight of the very fast

A

high visual acuity for accurate navigation, predation, predator avoidance.

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19
Q

vestigial remnants

A

primitive structure and no longer believed to be important for survival

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20
Q

define metazoans

A

any of a group (Metazoa) that comprises all animals having the body composed of cells differentiated into tissues and organs and usually a digestive cavity lined with specialized cells.

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21
Q

Hox gene, PAX6

A

encodes a transcription factor essential for brain and eye development.

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22
Q

does loss of function in the pax gene effect as homozygous or heterozygous?

A

effects both and two pox genes that are loss will cause failure of eyes to develop at all

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23
Q

rhabdomeric photoreceptors - (for protostome invertebrates)

A

maximize membrane surface area with microvilli projecting from the apical surface

apical surface is rotated 90o with respect to ancestral position

This lateral bed of (dendritic) microvilli form the rhabdom.
can vary in shape

second messenger signal transduction via
phospholipase C (PLC)/inositol phosphate (IP3) pathway
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24
Q

what are the specialized phtotoreceptor cells that detect and transduce light?

A

rhabdomeric and cilliary

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25
Q

ciliary photoreceptors

A

maximize membrane surface area via highly folded cilium (outer segment) projecting from the apical surface of the cell body

form rod and cone photoreceptors

use glutamate as a neurotransmitter

second messenger signal transduction via
phosphodiesterase (PDE) altering [cGMP] pathway

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26
Q

cillary vs rhabsomeric

A

rhabodemeric

  • used for invertebrates
  • SA increases with microvilli
  • secondary messenger is phospholipase C (PLC)/inositol phosphate (IP3) pathway

ciliary

  • used for vertebrates
  • SA increases with cilium
  • phosphodiesterase (PDE) altering [cGMP] pathway
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27
Q

macula degeneration

A

can be wet or dry

wet= get vascularization of retina which u don’t want blood getting in the way of where light is coming from

definition: if u lose all of the photoreceptors, u will go blind

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28
Q

define rhabdom

A

This lateral bed of (dendritic) microvilli which act as the receptors

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29
Q

cause of blind spot

A

The natural blind spot (scotoma) is due to lack of receptors (rods or cones) where the optic nerve and blood vessels leave the eye.

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30
Q

what creature has both rhabdom and ciliary photoreceptors?

A

Ancestral bilaterians and larva platenera

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31
Q

role of each photoreceptor in planaris larva

A

The eyes contain rhabdomeric photoreceptors. These enable the larvae to detect and swim towards light sources.

ultraviolet light activates ciliary photoreceptors, whereas cyan, or blue-green, light inhibits them. Shining ultraviolet light onto Platynereis larvae makes the larvae swim downwards. By contrast, cyan light makes the larvae swim upwards. In the ocean, ultraviolet light is most intense near the surface, while cyan light reaches greater depths. Ciliary photoreceptors thus help Platynereis to avoid harmful ultraviolet radiation near the surface.

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32
Q

ommatidum

A

contains six to eight sensory receptors arranged under a cornea and refractile cone and is surrounded by pigment cells, which adjust the intensity of light. Each ommatidium can act as a separate eye and is capable of responding to its own visual field.

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33
Q

describe the arthropod/insect compound eye

A

Insect eyes can contain 3000 (fruitfly) - 25,000 (dragonfly)
rhabdomeric photoreceptors per eye.

The compound eye is composed of multiple ommatidia,
each containing multiple photoreceptor cells.

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34
Q

describe the Cephalopod Camera Eye

A

The cephalopod retina contains 20,000 - 50,000

rhabdomeric photoreceptor cells/mm2.

35
Q

describe the vertebrate camera eye

A

The vertebrate retina contains millions of ciliary photoreceptor cells.

Many vertebrates have a recessed structure, the fovea,
which is the point of highest visual acuity.

The human fovea has ~200,000 photoreceptors/mm2 .

The avian (bird) fovea may have 400,000 - 1,000,000 photoreceptors/mm2, depending on species.

Raptors (birds of prey) have two foveas (shallow and deep foveas where the deep one helps with acuity) . Lots of dots!

36
Q

define fovea

A

a small depression in the retina of the eye where visual acuity is highest

37
Q

pigment

A

is a substance that changes the color

of reflected or transmitted light via wavelength-selective absorption.

38
Q

photopigment

A

biological pigment used by a living organism to absorb light.

39
Q

absorption spectrum

A

The range of wavelengths that a photopigment can potentially absorb
comprise the

40
Q

action spectrum

A

The range of wavelengths capable of driving a biological process
is the

41
Q

the pigment is responsible for facilitating that process IF

A

Close correspondence between the absorption spectrum of a pigment and
action spectrum of a biological process associated with that pigment

42
Q

what is the peak of the wavelength of the relative absorption?

A

500 nm

43
Q

chromophore (11-cis retinal)

A

Vitamin A (all-trans retinol) is converted in the retina to the 11-cis-isomer of retinaldehyde or 11-cis-retinal. 11-cis-retinal functions in the retina in the transduction of light into the neural signals necessary for vision.

The 11-cis retinal in photoreceptors is covalently bound to an opsin signaling protein to form a visual pigment molecule. In the presence of light, 11-cis retinal is isomerized to all-trans retinal, and the straightening of the polyene chain activates the opsin

44
Q

opsin

A

a protein which forms part of the visual pigment rhodopsin and is released by the action of light.

determines the wavelength of light to which pigment is sensitive

is a protein - encoded by DNA, so variable…
among species
among individuals of the same species
within a single individual

All are members of the G protein-coupled receptor (GPCR) superfamily.

45
Q

chromophore

A

The prosthetic group (chromophore) confers light sensitivity to the protein.

46
Q

Type I opsins

A

bacteria and some algae (all-trans chromophore)

47
Q

Type II opsins

A

all eumetazoans (11-cis chromophore)

48
Q

Upon isomerization

A

visual pigments trigger a metabotropic

second-messenger cascade, eliciting a receptor potential

49
Q

rhodopsin

A

ancient G-protein coupled receptors.
vertebrate rod photoreceptor pigment

extremely light sensitive
photobleaches upon exposure to light
returns to unbleached isomer in absence of light
confers high sensitivity to light/night vision

50
Q

blue cone

A

Short Wavelength Senstive (SWS) Opsin has a λmax of 430nm.

51
Q

green cone

A

Medium Wavelength Sensitive (MWS) Opsin has a λmax of 530nm.

52
Q

red cone

A

Long Wavelength Sensitive (LWS) Opsin has a λmax of 560nm.

53
Q

blue photopsin vs rhodopsin

A

many amino acid substitutions

54
Q

green photopsin vs red photopsin

A

many amino acid substitutions

55
Q

red photopsin vs green photopsin

A

many identical amino acids

56
Q

plural of rhabdomere

A

rhabdome

57
Q

what insect has more ommatidia/unit area than any other arthropod.

A

dragon fly compound eye

As aerial predators, they have evolved high visual acuity that allows them to localize and capture small, flying prey in mid-flight.

58
Q

light gathering in the ommatidium

A

outer/top section
-cornea, derived from cuticular corneagen (epidermal cells that take mucus from cornea mold formed) cells

-crystalling cone, derived from cuticular Semper’s (cone cells) cells
These focus incoming light onto the photoreceptor of the crystal part

59
Q

light-sensing segment (photoreceptor)

A

lower/bottom section
-light goes to 7-8 rhabdomeric retinula cells (photosensitive cells)

-Microvilli (dendritic processes) form the rhabdomere of each cell.
Rhabdomeres converge in the center to form the rhadom.

60
Q

iris

A

prevent light from scattering among ommatidia, isolating each ommatidium from its neighbors.

61
Q

optic nerve aka cranial nerve II

A

transfer visual information from the retina to the vision centers of the brain via electrical impulses.

Retinula cell axons pass through a basement membrane

62
Q

protocerebrum

A

(visual center), located in the anterior portion of the brain
where visual stimuli are processed and output is generated.

63
Q

location of primary and secondary iris/pigment cells

A

closest to the cornea: primary iris/pigment cells

closest to the base:

64
Q

what two types of ommatidum compound eye have?

A

photopic (apposition)

scotopic (superposition)

65
Q

photoptic

A

have a crystalline cone touching (in apposition to) the rhabdome
are the most common type of compound eye
are found in diurnal insects
have low sensitivity to light
confer high resolution
have relatively short ommatidia, each of which
has a relatively small field of view
produces an inverted image
The rhabdom averages the light received by the eye.
Multiple, inverted images are combined (and flipped) in the brain

66
Q

scopotopic

A

have a “clear zone” between crystalline cone and rhabdom
The “clear zone” contains crystalline tracts
These arise from retinula cells and act as “light guides”

67
Q

phototopic vs scopotopic

A

phototopic is during the day time so it is diurnal, very common, has low sensitivity, high resolution, short ommitilda, and has inverted images

scopotopic is the opposite

68
Q

causes of photopic having short ommatilda?

A

has a relatively small field of view
produces an inverted image
The rhabdom averages the light received by the eye.

69
Q

eff of scopotopic having long ommatilda?

A

At night, pigments in secondary pigment cells migrate to cell apices

Incoming light can stimulate unshielded rhabdomes of neighboring ommatidia
Images from each ommatidium are superimposed on each other.
Visual input to the brain comprises a single, un-inverted image.

70
Q

cornea

A

transparent, colorless “window” transmits light into the eye helps focus light onto the retina.

71
Q

pupil

A

aperture (hole/opening) through which light enters the eye

72
Q

iris

A

pigmented “shutter” contracts or relaxes to change aperture, controlling light admission.

73
Q

lens

A

transparent, colorless crystalline disc fine-focuses light onto the retina.

74
Q

anterior chamber / segment

A

fluid-filled space between cornea and iris

75
Q

anterior humor

A

fluid in the anterior chamber

76
Q

posterior chamber/segment

A

fluid-filled space between lens and retina

77
Q

posterior humor

A

aqueous gel in the posterior chamber

78
Q

retina

A

layer of specialized neurons that lines proximal interior of the eyeball
senses light, generates RPs and APs that travel through the optic nerve to the brain

79
Q

fovea

A

small, recessed retinal spot with the highest cone density and thus, highest visual acuity

80
Q

macua

A

(primates only) unrecessed retinal spot with a high density of cone photoreceptors, and housing the fovea.

81
Q

facet

A

corneal lens for individual ommatidium

82
Q

primary iris/pigment cells

A

closest to the cornea

83
Q

secondary iris/pigment cells

A

closest to the base:

bil 360 (11 decks)

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