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Neuroscience 3 > Phototransduction > Flashcards

Phototransduction Flashcards

1
Q

major trade off between compound and refractive eyes

A

compound- wide range of wave lengths

refractive- high resolution

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2
Q

what is the major refractive element in the eye

A

cornea

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3
Q

choroid layer

A

pigmented epithelium w/ blood vessels

includes iris

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4
Q

aqueous humor circulation

A

produced by ciliary epithelium (replaced 10-20x per day)- circulates in the anterior chamber and is cleared through the canal of schlemm

build up can lead to pressure and damage to the eye- called glaucoma

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5
Q

describe the passage of light from outside the eye to retinal processing

A

cornea- anterior chamber- iris/pupil - lens - vitreous humor - retina

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6
Q

ciliary muscles

A

control the shape of the lens. when the muscle contracts, lens gets rounder, enables close vision

controlled by parasympathetics- cn3 (contraction) and sympathetics (superior cervical ganglion- dilation)

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7
Q

accomodation loss

A

w/ age, lens looses its elasticity, and cannot reform rounded shape

pronounced by age 45

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8
Q

myopia

A

eyeball too long or cornea too curved, focal plane is in front of retina and you cant see far away

nearsighted– concave lenses

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9
Q

hyperopia

A

focal plane falls behind retina, not enough fractive power d/t short eyeball or flat lense

farsighted- convex lenses

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10
Q

babies are born w/ what condition?

A

hyperopia

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11
Q

cataracts

A

lens gets opaque and it interferes with vision- can be d/t crystallins

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12
Q

what happens to light not captured by retina

A

absorbed by pigmented epitherlium on the back of the eye

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13
Q

why does the fovea have the greatest acuity?

A

1 it has cones
2 tightly packed photoreceptors
3 other neuronal cells pulled to the side, resulting in less distortion

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14
Q

tapetum lucidum

A

contains guanine crystals- reflects light back thru retina and gives photoreceptors a second chance

increases sensitivity- night vision

decreases acuity

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15
Q

retinal detachment

A

a separation forms b/t pigmented epithelium and photoreceptor layers- brings photoreceptors out of focal plane and away from nutrients

occurs b/c of development- optic stalk invaginates and forms an optic cup- w/ outer layer becoming neural pigmented epithelium and inner layer becoming neural retina

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16
Q

macular degeneration

A

wet- involves tissue degradation and abnormal blood vessel growth

dry- deposition of yellowish protein and lipid aggregates called drusen

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17
Q

describe the 3 main parts of a photoreceptor

A

synaptic terminal- vesicles designed for transmitter release

inner segment- includes nucleus and most of cellular synthetic machinery

outer segment- connected by cilium, segment is filled w/ disks containing photopigments.

18
Q

are there more rods or cones?

A

100 mil rods

5 mil cones

19
Q

photoreceptors do not divide. what do they do instead?

A

produce new disks- 3/hour

20
Q

how are rods specialized

A

sensitivity- have more photoreceptors and are longer, so better at capturing light. rods amplify light signals more than cones. large degree of convergence on a given bipolar cell, increasing sensitivity but at the expense of resolution

night vision- most stimuli too weak to excite cones, but rods threshold of activation is about starlight

21
Q

how are cones specialized

A

temporal resolution- cones respond faster

spatial resolution- less convergence on bipolar cells and conical shape gives the fovea/cones better resolution

color vision- 3 types of cones w/ photoreceptors sensitive to different wavelengths. rods only have one photopigment

22
Q

what is the response to light from either rods or cones

A

hyperpolarization

23
Q

dark current and response to light

A

in the outer segment of rods/cones. cGMP gated channels allow a depolarizing current of Na and Ca into the cell.

this depolarization allows voltage gated Ca to remain open, which causes glutamate to be continuously released

in response to light, the cGMP disappears and those channels close, hyperpolarizing the cell, turning off Ca voltage gated channels, and halting the release of glutamate

24
Q

biochemistry of phototransduction

A

rhodopsin is in the disk membranes, and activation by light causes it to isomerize from cis to trans.

it then interacts w/ transducin. transducin then takes up GTP, and GTP-transducin activates phosphodiesterase

phosphodiesterase hydrolyzes cGMP, turning off the dark current

25
Q

rhodopsin kinase

A

usually inhibited by cGMP and Ca, decreases in those solutes cause it to phosphorylate rhodopsin. this causes rhodopsin to bind arrestin, which dissociates retinal from opsin.

the retinal is not very soluble and so is transported to the pigmented epithelium. the all-trans retinal becomes all trans retinol, which is the precursor to 11-cis retinal

vitamin a is not synthesized so it is important that it is recycled

26
Q

photoreceptor adaptation

A

cGMP synthesis is tied to Ca. A decrease in Ca signals bright light and cGMP lacks. however, guanate cyclase responds to the lack of Ca by producing more cGMP, which eventually opens up dark current channels, inhibiting the eye and “adapting” it to a brighter baseline

27
Q

what determines the optimal wavelength for a visual pigment

A

the opsin moiety determines the wavelength

28
Q

what wavelengths do cones absorb best?

A

420, 531, and 558 nm

29
Q

why are blue and red/green color blind syndromes inherited differently?

A

red/green are on the x chromosome and blue is on the 7th chromosome

30
Q

m v p cells

A

ganglion cells

magnocellular- large receptive fields- movement detection

parvocellular- small receptive fields- color vision

31
Q

characteristics of ganglion receptive fields

A

roughly circular

non homogenous- center and surround

center and surround cause opposite results

32
Q

w type ganglion

A

not center/surround

contain melanospin- sensitive to blue

important for circadian rhythms- see best at dawn and dusk

33
Q

difference between on and off center bipolar cells

A

on center

on center cells have bipolar cells with metabotropic, g protein coupled glutamate receptors. when stimulated but glutamate, lead to k channel activity and hyperpolarization

off center cells

bipolar cells with nmda/ampa ionotropic receptors, causing glutamate to open channels and allow cations to depolarize

34
Q

what information can be gained from the on/off center organization?

A

where the edges are

35
Q

strategies for treating vision loss

A

virus mediated expression of photoreceptor genes

photoreceptor precursors gene therapy

lens endogenous stem cells

artificial retinas

36
Q

retinitis pigmentosa

A

photoreceptor degeneration

37
Q

suprachaismatic nucleus

A

nucleus in hypothalamus receiving w type ganglion cell innervation playing a role in circadian rhythms

38
Q

inputs to superior colliculus

A

coordinates visual, somatic and auditory info in a topographic organization

responsible for adjusting movements of the head, neck and eyes

39
Q

projections to pretectal area

A

w cells project to ew nucleus, thru CN3 to the ciliary ganglion (pupillary sphincter) to generate the pupillary reflexes

40
Q

lateral geniculate

A

receives most retinal projections- topographic representation of the retina

it has 6 layers, 3 from each eye. outer 4 are P layers, inner 2 are M layers

Neuroscience 3 (12 decks)

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