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ZOOL 461 > Vision > Flashcards

Vision Flashcards

1
Q

Light energy is defined in two ways. What two ways is light energy defined as?

A
  1. Particle - photon
  2. Wave - wavelength
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2
Q

What part of the electromagnetic radiation spectrum can humans best detect?

A

The visible light spectrum

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3
Q

Why are humans best able to detect visible light?

A

Most of the energy that is being put off by the sun is visible light, so its not a surprise that we can see these wavelengths

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4
Q

What is the purpose of the human eye?

A

To gather and focus light onto the fovea (involves refraction/bending of light)

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5
Q

The better we can focus light…

A

The better our visual acuity (measure of how well someone can see)

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6
Q

Convex lens (converges/diverges) light

A

Converges

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7
Q

Concave lens (converges/diverges) light

A

Diverges

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8
Q

(More/less) refraction is required to see objects that are close
- Explain why

A

More, because light rays coming from the object are diverging which requires more refraction

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9
Q

(More/less) refraction is required to see objects that are far
- Explain why

A

Les, because light rays coming from the object are mostly parallel to the back of the eye

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10
Q

Emmetropia

A

Normal vision
- Far source focused on retina without accomodation (shape change) of lens
- Near source focused on retina with accomodation of lens

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11
Q

Myopia

A

Nearsighted (able to see things that are close but not far away)
- Far source focused in front of retina (where retina would be in eye of normal length)
- Near source focused on retina without accommodation

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12
Q

How is myopia corrected? Explain how

A

Using a concave lens
- Diverges light rays before they reach the eye
- Far source focused on retina without accommodation
- Near source focus on retina with accommodation

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13
Q

Hyperopia

A

Farsighted (able to see things that are far but not close)
- Far source focused on retina with accommodation from lens
- Close objects focused behind retina, even with accommodation

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14
Q

How is hyperopia corrected? Explain how

A

Using a convex lens
- Converges light rays before they reach the eye
- Far source focused on retina without accommodation
- Near source focused on retina without accommodation

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15
Q

Presbyopia

A

“Old” sighted
- Hyperopia in older people due to lens losing flexibility
- Far source focused on retina with accommodation from lens
- Near source focused behind retina even with accommodation from lens

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16
Q

How is presbyopia corrected? Explain how

A

Corrected with a convex lens, which converges light rays before they reach the eye
- Far source focused on retina without accommodation
- Near source focused on retina with accommodation

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17
Q

Function of cornea

A

Does the majority of light refraction
- Static, can’t change shape
- Roughly symmetrical

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18
Q

What is astigmatism?

A

See double vision due to uneven refraction from the cornea (cornea is asymmetrical)

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19
Q

Anterior chamber

A

Fluid-filled and located behind the cornea
- Contains nutrients, bathes the tissues behind the cornea with O2-rich and nutrient-rich fluid

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20
Q

Anterior chamber is filled with…

A

Aqueous humour

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21
Q

What produces the aqueous humour?

A

The ciliary body

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22
Q

What does the aqueous humour drain into the anterior chamber through?

A

The canals of Schlemm
- connects with some of the vessels of the lymphatic system (gets recycled)

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23
Q

True or false: the aqueous humour is constantly being produced

A

True
- At a rate of 5 mL/day

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24
Q

Glaucoma

A

Due to increased intraocular pressure, due to narrowing of canals of Schlemm (amount of aqueous humour drained off is less than amount of aqueous humour produced)
- Darkening periphery because the outer axons of the optic nerve get damaged first (irreversible)

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25
Q

Iris function

A

Controls the amount of light that reaches the retina
- Controls the diameter of the pupil
- Important because too much light can damage the photoreceptor

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26
Q

Iris muscles are under control of the…

A

Autonomic nervous system

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27
Q

The iris is composed of which two muscles?

A
  1. Circular (constrictor) muscle runs circularly
  2. Radial (dilator) muscle runs radially
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28
Q

Parasympathetic stimulation of iris results in…

A

Pupillary constriction
- Circular (constrictor) muscle contracts

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29
Q

Sympathetic stimulation of the iris results in…

A

Pupillary dilation
- Radial (dilator) muscle contracts

30
Q

Function of the lens

A

Responsible for the remaining refraction of the light (the light not refracted by the cornea already)

31
Q

Lens is made of what material?

A

β crystalline proteins

32
Q

What controls the lens shape?

A

Ciliary muscles bound to suspensory ligaments

33
Q

When ciliary muscles contract…

A

Suspensory ligaments are slackened, so lens is round and refracts light more
- When looking at close objects

34
Q

When ciliary muscles relax…

A

Suspensory ligaments are taut, so lens is longer and refracts light less
- When looking at far objects

35
Q

Cataracts

A

Opaque lens when β crystalline proteins start to denature -> causes lens to get cloudy because proteins get folded up
- Lens becomes less flexible

36
Q

True or false: there is no treatment for cataracts

A

False
- While there isn’t a lot of treatment for cataracts, lens replacements are still done although the prosthetic lens is much less flexible and less able to accomodate

37
Q

Retina

A

Back layer of the eye where all the photoreceptors are located

38
Q

Fovea

A

Divit in retina that has the greatest visual acuity

39
Q

Optic nerve

A

Bundle of axons that carries all of the light information

40
Q

Optic disc

A

Where the blood vessels enter the eye

41
Q

True or false: there is no transduction of light energy at the optic disc

A

True
- We have a blind spot here

42
Q

Which order of cells is activated as light travels through the eye?

A

Light -> photoreceptor
-> bipolar cells -> Ganglion cells

43
Q

Function of amacrine and horizontal cells?

A

Increase our ability to detect slight differences in the light striking the eye (by changing the firing activity of surrounding cells)

44
Q

The axons of the ganglion cells…

A

Converge into the optic nerve

45
Q

Cones are ___chromatic, rods are ___chromatic

A

Trichromatic (there’s 3 types of cones), monochromatic

46
Q

There are more (cones/rods) than (cones/rods) in the eye

A

More rods than cones

47
Q

Cones are more concentrated around the…

A

Fovea

48
Q

Rods are more concentrated around the…

A

Periphery of the eye

49
Q

Intense light is needed to activate the (cones/rods), while (cones/rods) can activate even with low light

A

Cones, rods

50
Q

(cones/rods) are responsible for most of our night vision

A

Rods (vision in the dark when there’s very little sources of light)

51
Q

Phototransduction occurs in the…

A

Membrane of the outer segment of the rods and cones

52
Q

Describe the structure of the outer segment in rods and the implications of this

A

The outer segment membrane on rods contains discs, which are bulges of phospholipid bilayer which increase surface area. This increased surface area allows for more packing of more photopigments.

53
Q

Describe the structure of the outer segment in cones and the implications of this

A

The outer segment membrane on cones has repeating folds, which increases the surface area (space) for photopigments

54
Q

The synaptic terminals of rods and cones are responsible for…

A

Releasing the neurotransmitter glutamate
- The amount of glutamate released depends on the membrane potential of the cells themselves

55
Q

True or false: rods and cones generate action potentials

A

False
- rods and cones do not generate action potentials themselves, but they do change their membrane potential, which changes the amount of glutamate released.

56
Q

Visual pigment(s) found in rods

A

Rhodopsin

57
Q

Visual pigment(s) found in cones

A

Blue(short wavelength): cyanolabe
Green (medium wavelength): chlorolabe
Red (long wavelength): Erythrolabe

58
Q

What two things is rhodopsin made up of?

A

Retinol (derivative of vitamin A) + opsin

59
Q

What can a deficit in vitamin A in your diet result in?

A

Loss of night vision due to decreased retinol

60
Q

When light is absent, rhodopsin is in what configuration?

A

When light is present, rhodopsin is in its 11-cis configuration

61
Q

When light is present, rhodopsin is in what configuration?

A

Rhodopsin is in its all trans version (metarhodopsin II)

62
Q

What are the steps to the phototransduction pathway? (8 steps)

A
  1. Light enters eye and hits rhodopsin.
  2. Rhodopsin changes configuration to all trans version (metarhodopsin II)
  3. When rhodopsin is activated, this activates G protein transducin
  4. Transducin activates cGMP phosphodiesterase, which converts cGMP into 5’GMP
  5. The decreased cGMP content in the photoreceptor decreases the activity of cGMP-gated channels, which pump Na+ into the cell
  6. Less influx of Na+ makes the cells hyperpolarize
  7. Hyperpolarizatoin results in less glutamate release
  8. Change in neurotransmitter release changes the signals of bipolar/ganglion cells to change the perception of light
63
Q

What is the “dark current”?

A

In the dark when there’s no light present, we have a constant influx (current) of Na+ through cGMP channels

64
Q

True or false: K+ is always flowing out of the photoreceptors

A

True

65
Q

In photoreceptors, what is working to maintain the membrane potential, especially in the dark when so much Na+ is flowing into the cell?

A

Na+/K+ ATPase

66
Q

What is the membrane potential of the photoreceptors at rest (i.e. when no light is present)?

A

~-50 mV (a little more positive than other RMPs)

67
Q

How do we see different colours if we only have 3 types of cone pigments?

A

The different cones absorb light maximally at different wavelengths. If a wavelength activates different cones (at different levels), these colours will mix to give a new colour

68
Q

What causes colourblindness?

A

Colourblindness is the result of disruption in any of the cones (lose the ability to distinguish between colours)

69
Q

Where are horizontal cells located?

A

Between photoreceptors and bipolar cells

70
Q

Where are amacrine cells located?

A

Between bipolar cells and ganglion cells

ZOOL 461 (11 decks)

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