Brainscape's Knowledge GenomeTM

Browse over 1 million classes created by top students, professors, publishers, and experts.


See full index

... > dark adaptation > Flashcards

dark adaptation Flashcards

1
Q

what is dark adaptation

A

how your eyes adapt to the dark to see in dimmer lighting conditions

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
2
Q

describe the structure of photoreceptors

A

the outer segment contains membranous discs - invaginations of the cell membrane which contain photopigments - colour pigments which absorb light

  • rhodopsin (rods)

photoopsin (cones)

each photopigment contains

light absorbing portion (chromophore)- i.e. - activated by light - retinal

and a protein called opsin

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
3
Q

what are the types of photopsin in cones

A

3 different types of photopsin in cones

corresponding to different wavelenghs of light

opn1nw - green

opn1lw - red

opn1sw- blue

rods - rhodopsin

therefore 4 different types of photoreceptor

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
4
Q

what does each photopigment contain

A

each photopigment contains - a light absorbing portion - (chromophore) - retinal

and a protein called opsin

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
5
Q

what happens to retinal in phototransduction

A
  • retinal is the light absorbing portion (chromophere) - in a photoreceptor
    • a photon of light hits retinal meaning that 11 cis retinal isomerises to all - trans retinal
How well did you know this?
1
Not at all
2
3
4
5
Perfectly
6
Q

describe photoreceptors in dark conditions

A
  • in dark conditions - photoreceptors can be described as on - but because it is releasing a inhibitory neurotransmitter glutatmate
How well did you know this?
1
Not at all
2
3
4
5
Perfectly
7
Q

describe the state of photoreceptors on light conditions

A

relatively hyperpolarised

stops the release of glutatmate impulse

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
8
Q

what is bleaching

A

light causes disscoiation of 11 cis retinal with the opsin and conversion to 11 all trans retinal

11 trans retinal transported to the rpe to be converted back into 11 cis retinal then transported to the outer segement

until 11 cis retinal is bound again to its opsin - rhodopsin cannot detect more light

this bleaching means rhodopsin struggles to operate in bright conditions

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
9
Q

describe phototransduction in the dark

A
  • there= high levels of cGMP

these bind to sodium channels and keep them open - causing a influx of sodium- causing depolarisation- causes release of nt called glutamate - transmitter causes graded potentials in bipolar cells

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
10
Q

describe phototransduction in the light

A
  • light = absorbed by the photopigment

hits 11 cis retinal turns into 11 trans retinal and dissociates from its opsin

  • levels of cGMP decrease

sodium channels close - less sodium entering the cell

the cell hyperpolarises

calcium channels close

stops the release of glutamate

tells bipolar cells that their = light

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
11
Q

what is bleaching a result of

A
  • it takes a long time for retinal and opsin to be turned back into their orginal configuration
How well did you know this?
1
Not at all
2
3
4
5
Perfectly
12
Q

describe the function of rods and its opsin

A

rods give black and white vision/ night vision and sense contrast and brightness motion - their opsin is rhodopsin

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
13
Q

what is the function of cones and its opsin

A

cones give fine resolution and colour vision - they have three opsins absorbing different wavelengths to provide a visible spectrum

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
14
Q

what do discs contain

A
  • discs contain the photopigmenrs and are found in the photoreceptor outer segments
How well did you know this?
1
Not at all
2
3
4
5
Perfectly
15
Q

what is phototransduction

A

phototransduction is the conversion of light to a neural impluse

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
16
Q

what happens when retinal absorbs a photon

A

retinal absorbs a photon , causing a cascade resulting in hyperpolarisation of the cell and cessation of glutamate release (inhibitory neurotransmitter)

17
Q

what is bleaching

A

bleaching means that rhodposin is unable to operate under bright conditions

18
Q

define dark adaptation

A

the process including dilation of the pupil , increase in sensitivity of the retinal rods and regeneration of rhodopsin by which the eye adapts to conditions of reduced illumination

19
Q

what are the three types of vision

A

photopic - cones dominate , bright light

scotopic - rods dominate low light

mesopic - overlap between the two - both cones and rods- twilight/ transitional

20
Q

describe how the different photoreceptors operate in different lighting conditions

A

rods respond to low luminance light - dominate scotopic vision

cones respond to high luminance light and they dominate photopic vision

mescopic vision is the range where the two are both working together

21
Q

how is luminance defined and measured

A

luminance is the measurement of the brightnes of light emitted from a light source

illuminance is a measurment if how bright the reflection is of emitted light from an object

unit = candela/m2

22
Q

describe range of luminance

A

in photopic condtiions it goes up to 3. 000,000 cd/m2

in mesoscopic it goes up to 3 cd/m2

in scotopic it gors up to 0.0003cd/m2

23
Q

what is the process of dark adaptation

A

moving from light into dark conditions causes a period of poor vision

process wherby the eye becomes more sensitive to light in areas of low luminance is dark adpatation

24
Q

what is visual threshold

A

the sensitivity of the eye to light can be described using the visual threshold

the minimum luminance of a test spot that can be percieved (produce a visual sensation) - minimum amount of light we can see

in the dark the eye becomes progressivley more sensitive to light stimulation until the threshold reaches a minimum after approx 30 mins

25
Q

what happens to the eye in light

A

pupil is constricted to focus light onto the cones

rhodopsin = bleached

26
Q

what happens to the pupil in the dark

A

pupillary dilation - maximises light and allows it to hit peripheral rods

regeneration of 11 cis retinal bound with its opsin

27
Q

how is dark adaptation tested

A

light adaapt observer to bleach photopigment

large flashing 420nm wavelength light against dark background (stimulates both rods and cones)

observer decreases luminance of test light until it is barley percieved and continues to do so

28
Q

describe the dark adaptation curve

A

2 distinct regions of recovery seperated by rod - cone break

1st component resulting from increase in cone senstivity

2nd component resulting from increase in rod sensitivity

minmium threshold reached after 30 mins

under these conditions we say that the photopigments are fully regenerate

visual threshold improves by 6 log units - 1, 000,000 times

rods are adpating during the cone phase - however cones are more sensitive at this point due to rod bleaching

cone plateau - 5-8 mins is the visual threshold for the cone system

rod plateau- 30 mins rod threshold

29
Q

what factors affect dark adpation

A

duration and intensity of pre- exposure

size/location of test spot

length of exposure of test light

retinal positon

stimulus wavelength

pupil size

age

30
Q

what is the limiting factor of dark adpatation

A

the dark adpation and regeneration of rhodopsin are dependent on the local conc of 11 cis retinal - this is quicker in cones which is why the first phase is in cones

limiting factor for recovery after a large bleach is rate of 11- cis retinal is delivered to opsin in bleached photoreceptors

31
Q

what is night blindess called

A

night blindness is referred to as nyctalopia
retinis pigmentosa - rod cells gradually lose function resulting in progressive nyctalopia and loss of peripheral visual field

vitamin a defficency - vit a is necessary for regeneration of 11 cis retinal

32
Q

what are the three types

A

photopic - daytime - cones ]

mesoscopic - twilight/ transitional - cones and rods

scotopic - night vision - rods only

33
Q

what does visual threshold refer to

A

the minimum luminance of a test spot that can be percieved (produce a visual sensation) is the visual threshold

34
Q

what does dark adaptation involve

A

dark adaptation involves pupillary dilation and regeneration of 11 cis retinal

35
Q

what do the two discreete area of recovery on the classic dark adaption curve show

A
  • they show a cone recovery phase and a rod recovery phase seperated by the rod cone break
36
Q

when is max cone sensitvity and max rod sensitivity reached

A

max cone sensitivity is reached after 8 mins - followed by rod sensation until the rod plateau - minimum threshold after 30 mins

at this the point is maximally dark adapted

... (14 decks)

Brainscape helps you reach your goals faster, through stronger study habits.
© 2024 Bold Learning Solutions. Terms and Conditions