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Physiology > The Eye > Flashcards

The Eye Flashcards

1
Q

What are the first steps of vision?

A
  1. Transmission and refraction of light by the optics of the eye
  2. The transduction of light energy into electrical signals by photoreceptors
  3. The refinement of these signals by synaptic interactions within the neural circuits of the retina
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2
Q

Visual processing pathway 3 step diagram

A
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3
Q

Full visual processing pathway diagram

A
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4
Q

What do photoreceptors in the retina contain?

A

Pigments that absorb light reflected by objects

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5
Q

Wavelength defn

A

Distance between two peaks of the electromagnetic wave

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6
Q

What does wavelength relate to?

A

Light colour: when white light diffracts through a prism it splits into the separated l (rainbow effect)

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7
Q

Transparent media function

A

Will bend the light to focus it in the retina

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8
Q

Reflection defn and diagram

A
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9
Q

Refraction defn and diagram

A

Bending of light rays when they travel from one media to the other.

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10
Q

Absorption defn and diagram

A

Transfer of light energy to a particle. Black objects absorb all the l of visual light, green objects absorb all except green, etc.

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11
Q

Anatomy of the eye x 5

A
  • Pupil
  • Iris
  • Cornea
  • Extraocular muscles
  • Optic nerve
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12
Q

What is the pupil?

A

Opening that allows the entry of light

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13
Q

What is the iris?

A

Pigmentation that provides eye colour.

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14
Q

What other than pigmentation does the iris contain and function?

A

Contain two muscles to regulate the size of the pupil

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15
Q

What is the cornea?

A

Transparent surface covering the front eye. It continues in the sclera, the white of the eye

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16
Q

Where does the extraocular muscle insert and function?

A

Inserts in the sclera, to control eye movement

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17
Q

Where does the optic nerve exit?

A

At the back of the eye

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18
Q

Anatomy of the eye diagram

A
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19
Q

Optics

A

Cornea and lens will diffract light to focus it in the retina. The lens will accommodate to different distances.

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20
Q

Far point optics diagram with focal distance draw

A
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21
Q

Near point optics diagram draw

A
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22
Q

Myopia diagram

A

Nearsightedness

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23
Q

Hyperopia diagram

A

Farsightedness

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24
Q

What is the retina a part of?

A

CNS

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25
Q

Most direct pathway to the brain

A

Photoreceptors ➡ Bipolar cells ➡ Ganglion cells

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26
Q

What are the only light-sensitive cells in the retina?

A

Photoreceptors

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27
Q

What are the only output cells in retina?

A

Ganglion cell axons (optic nerve) to higher CNS centres

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28
Q

What are horizontal and amacrine cells?

A

Local interneurons and modulate transmission onto bipolar and ganglion cells

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29
Q

Retina pathway to brain and cells diagram

A
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30
Q

Retina laminar organisation and layers

A
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31
Q

What do photoreceptors do?

A

Transform electromagnetic radiation into electrical signals

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32
Q

Rod and cone diagram

A
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33
Q

What does the outer segment of the retina contain?

A

Membrane disks, with light-sensitive photopigments that absorb light and will trigger changes in membrane potential

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34
Q

Rods make up

A

One photopigmentblack / white vision, lot of membrane disks (more sensitive to light)

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35
Q

Cones make up

A

3 photopigments-colour vision

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36
Q

Rods function

A

Night vision

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37
Q

Cones function

A

Daylight vision

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38
Q

What is the fovea enriched in?

A

Cones

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39
Q

What is the periphery enriched in?

A

Rods

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40
Q

Where are cones tightly packed?

A

In the fovea

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41
Q

Where are cones widely spaced?

A

In the periphery

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42
Q

Size of receptor fields in periphery and what does this mean?

A

Larger - lower resolution

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43
Q

Many photoreceptors feeding (convergence) into individual ganglion cells in the periphery, what does this mean?

A

More rods and greater input in the periphery (higher sensitivity)

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44
Q

Lateral displacement of the layers above the photoreceptor at the fovea →

A

Light hits directly without scattering

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45
Q

Describe fovea input

A

More cones and no convergence of input in the fovea: lower sensitivity
No convergence of input and direct light input in the fovea: higher resolution

(no convergence = one photoreceptor → one ganglion cell)

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46
Q

Rods light sensitivity

A

Low spatial resolution but very sensitive to light; saturated in very bright light → night vision

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47
Q

Cones light sensitivity

A

High spatial resolution but relatively insensitive to light; not operating in dim light → day vision

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48
Q

What do rods contain?

A

Contain photopigment rhodopsin

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49
Q

What are rods sensitive to

A

All visible wavelengths

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50
Q

Rods sensitivity to light

A

High sensitivity

51
Q

When are rods used

A

Night vision

52
Q

Where are rods located?

A

All over the retina except fovea

53
Q

Total number of rods

A

100 million

54
Q

What is each cone sensitive to?

A

One type of light

55
Q

Do cones or rods require more energy to be activated?

A

Photopigments of cones require more energy to be activated

56
Q

What do cones contain?

A

Cone opsins (3 types, with different absorption for red, green or blue light)

57
Q

Sensitivity of cones to light

A

Low sensitivity to light

58
Q

Function of cones

A

Daylight sight

59
Q

Location of cones

A

Located mainly in the macula, and especially the central area of the macula, the fovea

60
Q

How many cones in total?

A

6 million total

61
Q

What is phototransduction?

A

Conversion of light energy into membrane potential changes

62
Q

Rods x 6 points

A
  • Contain photopigment rhodopsin
  • Sensitive to all visible wavelengths
  • High sensitivity to light
  • Night vision
  • Located over all retina (except fovea)
  • 100 million in total
63
Q

Cones x 6 points

A
  • Contain photopigments cone opsins (3 types, with different absorption for red, green or blue light)
  • Low sensitivity to light
  • Daylight sight
  • Located mainly in the macula, and especially the central area of the macula, the fovea
  • 6 million in total
64
Q

Describe phototransduction membrane potentials

A

Graded changes in membrane potentials (the only neurons firing action potentials are ganglion cells) → change in rate of transmitter release

65
Q

Phototransduction in dark

A

Membrane depolarised, Ca2+ channels open, rate of transmitter release is high

66
Q

Phototransduction in light

A

Hyperpolarisation, Ca2+ channels close, decrease in rate of transmitter release

67
Q

Stimulus of classic GPCR

A

Chemical

68
Q

Receptor activation of classic GPCR

A

G protein binds GTP

69
Q

Enzyme of classic GPCR

A

Activation

70
Q

Second messenger of classic GPCR

A

Increase in second messenger levels

71
Q

Ion channel of classic GPCR

A

Increase / decrease conductance

72
Q

Stimulus of rhodopsin

A

Light

73
Q

Receptor activation of rhodopsin

A

G protein binds GTP

74
Q

Enzyme of rhodopsin

A

Activation

75
Q

Second messenger of rhodopsin

A

Decrease in second messenger levels

76
Q

Ion channel of rhodopsin

A

Decrease Na+ conductance

77
Q

Classic GPCR vs Rhodopsin diagram

A
78
Q

What happens to photoreceptors in darkness and why?

A

Depolarised (-30mV) due to a “dark current” of Na+

79
Q

Phototransduction of rods in darkness process

A
80
Q

What happens to rods with light?

A

Photoreceptors will hyperpolarize with light

81
Q

Rhodopsin =

A

Opsin + Retinal

82
Q

Rods absorption of light process

A
83
Q

Rods hyperpolarisation with light process

A
84
Q

Phototransduction- signal amplification

A
85
Q

What does light do to photoreceptors?

A

Hyperpolarises

86
Q

What does darkness do to photoreceptors?

A

Depolarises

87
Q

What do responses of in the bipolar and ganglion cells varying depend on?

A

On the receptors they express and lateral modifications (horizontal and amacrine cells)

88
Q

What can bipolar cells be depolarised or hyperpolarised by?

A

Glutamate

89
Q

Hyperpolarisation expression

A

AMPA/Kainate R expression

90
Q

Depolarisation expression

A

mGluR6 expression

91
Q

Depolarisation = mGluR6 expression pathway

A

Bound to glutamate (during dark), mGluR6 causes closure of Na+ channels. Hyperpolarisation of photoreceptor by light reduces glutamate release, reduces mGluR6 binding and allows Na+ channels to open on the bipolar cell.

92
Q

Dark and light responses diagram

A
93
Q

What is the bipolar receptive field?

A

An area of retina where a stimulus will evoke a response in that bipolar cell

94
Q

Receptive field centre =

A

Direct connection from photoreceptors

95
Q

Receptive field surround =

A

Connection from photoreceptors through horizontal cells

96
Q

Response triggered in centre =

A

Opposite will be triggered by the surround

97
Q

How are bipolar cells classified?

A

According to their responses to light

98
Q

Types of bipolar cells

A
  • On-centre bipolar cells

* Off-centre bipolar cells

99
Q

ON-centre Bipolar cells

A

Depolarized by light, expressing mGlur6

100
Q

OFF-centre Bipolar cells

A

Hyperpolarized by light (as Photoreceptors), expressing AMPA / Kainate

101
Q

What is the area of retina where a stimulus will evoke a response in that ganglion cell called?

A

The receptive field of a ganglion cell

102
Q

What does each ganglion cell

A

A ‘centre’ and ‘surround’ to it’s receptive field

103
Q

Effect of centre vs surround

A

Light in the centre will have the opposite effect to light in the surround

104
Q

What do ganglion cells generate?

A

AP in the retina

105
Q

What are the only cells that produce APs in the retina?

A

Ganglion cells

106
Q

When do on-centre ganglions produce APs?

A

When light is shone on the photoreceptor that directly innervates it.

107
Q

What happens to off centre ganglions when light is shone on photoreceptor that innervates it?

A

Decreases APs

108
Q

When does the photoreceptor get hyperpolarised?

A

ALWAYS by light

109
Q

What can happen to AP firing in ganglion cell when hyperpolarised?

A

May increase or decrease

110
Q

What decreases APs when light is turned off?

A

On-centre ganglion cells

111
Q

What increases APs when light is turned off?

A

Off-centre ganglion

112
Q

When is there no change in firing rate?

A

When both centre and surround are in same level of illumination: A, C and E

113
Q

When is there the greatest difference in firing?

A

When you have most contrast between the centre and surround: B and E

114
Q

What is the antagonistic centre/surround effect mediated by?

A

Horizontal cells

115
Q

What do horizontal cells regulate?

A

Amount of transmitter released by photoreceptor onto bipolar cell

116
Q

Light at centre causes depolarisation of bipolar cell: process

A
  • Light hyperpolarises centre cone
  • Decreased release of glutamate from centre cone
  • Depolarisation of bipolar cell (mGluR6)
117
Q

What does addition of light to surround cause?

A

Reduces firing rate of on-centre

118
Q

Horizontal cell hyperpolarisation

A

Surround cone releases less glutamate onto horizontal cell

119
Q

Addition of light to surround process

A
  • Strong hyperpolarisation of horizontal cells
  • Reduced release of GABA from horizontal cell onto centre cone
  • Reduces hyperpolarisation of centre cone
120
Q

Reduced hyperpolarisation of centre cone ➡

A

Increased release of glutamate from centre cone ➡
Hyperpolarization of bipolar cell ➡
Hyperpolarization and reduced firing of GC

121
Q

Opsin ➡

A

Transducin → PDE → CNG Channel → Glu

122
Q

Light energy conversion

A

Converted to membrane potential changes in photoreceptor cells, through Opsin → Transducin → PDE → CNG Channel → GluC

123
Q

Membrane potentials in bipolar pathway

A

Glutamate information will be converted into membrane potential changes in bipolar (centre ON/OFF) and horizontal (surround ON/OFF) cells

Physiology (28 decks)

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