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Anatomy & Physiology > Chapter 15: Vision > Flashcards

Chapter 15: Vision Flashcards

1
Q

What are the components of the neural layer?

A
  • photoreceptors (rods & cones)
  • bipolar cells
  • ganglion cells
  • horizontal cell
  • amacrine cell
  • optic disk (blind spot)
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2
Q

Rods

A

night vision
- black/white vision
- more sensitive (low resolution)
- most in periphery of eye

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3
Q

Cones

A

day vision
- color
- less sensitive (higher resolution)
- most in fovea

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4
Q

What are the parts of the photoreceptor?

A
  • outer segment
  • inner segment
  • synaptic ending
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5
Q

What is the outer segment part of a photoreceptor?

A
  • catches light behind rods and cones
  • visual pigment shape changes
  • many rhodopsin discs
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6
Q

What is the inner segment part of a photoreceptor?

A
  • organelles
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7
Q

What is the synaptic ending of a photoreceptor?

A
  • neurotransmitter release
  • synapses release glutamine
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8
Q

What are discs made up of?

A

phospholipid bilayer

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9
Q

What is a visual pigment?

A

made up of retinal & opsin

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10
Q

What is retinal?

A
  • light absorbing chromophore
  • changes shape due to light
  • shaped like a key
  • derived from vitamin A
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11
Q

What is opsin?

A

G protein

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12
Q

How does retinal change in shape?

A

depending on exposure to light
- 2 shapes
–> 11-cis-retinal
–> all-trans-retinal

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13
Q

How is transmembrane potential affected when a photoreceptor is in the dark?

A
  1. Cyclic cGMP opens chemically gated Na+ channel
  2. Cyclic cGMP binds to Na+
  3. “dark current” occurs –> Na+ enters photoreceptor cell
  4. photoreceptor DEPOLARIZES (cell becomes more +)
  5. Photoreceptor synapses release glutamate (neurotransmitter)
  6. bipolar cells are inhinited –> no info reaches brain, this is how we tell what is darkness
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14
Q

What is the neurotransmitter used by the photoreceptor?

A

Glutamate

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15
Q

Is the neurotransmitter used by the photoreceptor excitatory or inhibitory?

A

Glutamate is inhibitory

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16
Q

How does the neurotransmitter used by the photoreceptor affect the postsynaptic cell?

A

Glutamate prevents brain from receiving information. This is how we perceive darkness

17
Q

Describe events that happen in photoreceptor upon exposure to light.

A

Phototransduction:
1. Opsin activation
- photon of light is absorbed by photopigment/chromophore
- 11-cis-retinal –> all-trans-retinal
- retinal is isomerized from 11-cis-retinal to all-trans-retinal (same compound but diff shape)
2. Activation of transducin & PDE
- opsin activates transfucin (G-protein, “on” switch)
- transducin activates PDE (phosphodiesterase)
- PDE breaks down cyclic cGMP
3. cGMP levels decrease & Na+ channels close
- when PDE breaks down cyclic cGMP, no more Na+ to bind to
- Na+ channels close
4. Membrane hyperpolarizes (becomes more -)
- pumps sodium out
- neurotransmitter release slows
5. bipolar cells are activated
- less glutamate, less inhibited
- as brightness increases, glutamate decreases
6. Ganglion cells are stimulated

18
Q

Which statement is True for “dark current” of photoreceptors.

a) the exit of Na+ out of the cell when light is not hitting the cell
b) the entry of Na+ into the cell when light is not hitting the cell
c) decrease in glutamate release
d) activation of bipolar cells

A

b) entry of Na+ into the cell when light is not hitting the cell

19
Q

When light strikes a photoreceptor it…
a) depolarizes and releases more neurotransmitter
b) depolarizes and releases less neurotransmitter
c) hyper-polarizes and releases more neurotransmitter
d) hyper-polarizes and releases less neurotransmitter

A

d) hyper-polarizes and releases less neurotransmitter (glutamate)

20
Q

In the light-adapted state…
a) photoreceptors are much more sensitive to stimulation
b) photoreceptors are much less sensitive to stimulation
c) we can only see color, and not black and white
d) colors are dull

A

b) photoreceptors are much less sensitive to stimulation

21
Q

What is bleaching of retinal?

A

cis- to trans-retinal
1. trans-retinal leaves opsin & travels to RPE (retinal pigment epithelium)
2. Retinal isomerase converts trans-retinal –> cis-retinal
- retinal isomerase enzymes are in RPE
3. cis-retinal is transported back to outer segments of photoreceptors

22
Q

What is regeneration of retinal?

A

changing of all-trans-potential –> 11-cis-retinal
1. cis-retinal binds to opsin, reforms photopigment

23
Q

Dark Adaptation

A

(light –> dark)
- use rods only
- light: rhodopsin is bleached
- dark: rhodopsin takes up to 40 mins to regenerate
- more regenerated rhodopsin –> more sensitive
- ex. going outside at night, cannot initially see many stars but if stay outside longer, can see more

24
Q

Light Adaption

A

(dark –> light)
- happens in seconds
- all rods are activated
- bleaching of rods
- decrease in sensitivity (switch from rod to cone vision)
- use color vision

25
Q

Pupil Dilation

A

changing of pupil opening to restrict amount of light going in to photoreceptors
- pupil dilate = let more light in (dark)
- pupil constrict = let less light in (light)

26
Q

What are the three types of cone opsins found in humans?

A
  • red (long wavelength)
  • green
  • blue (short wavelength)
27
Q

How many cone opsins does each photoreceptor have?

A

One cone opsin per one photoreceptor

28
Q

How do we see so many different colors?

A

through more or less stimulation of combinations of opsins

29
Q

What kind of light is seen if all three opsins (red, green, & blue) are stimulated?
a) purple
b) white
c) green
d) red

A

b) white light

30
Q

Dietary deficiency of vitamin A is likely to cause…
a) retinis pigmentosa
b) color blindness
c) night blindness
d) retinal detachment
e) increased retinal isomerization

A

c) night blindness

31
Q

Retinis Pigmentosa

A
  • most common disorder of transduction
  • onset @ 40 yrs old
  • begin to lose peripheral vision
  • left with tunnel vision
  • go completely blind
  • due to point mutation (changing of one amino acid) of rhodopsin
  • affects rods & cones –> both crumble
32
Q

Color Blindness

A

inability to tell colors apart
- due to missing cones

33
Q

Night Blindness

A
  • poor vision @ low light
  • caused by long deficiency of vitamin A - has to come from diet
  • can be reversed
  • retinal cannot be synthesized
34
Q

Does bleaching or regeneration occur first?

A

Bleaching then regeneration

35
Q
A

Anatomy & Physiology (10 decks)

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