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Ocular Block 7 > Retinal Histology > Flashcards

Retinal Histology Flashcards

1
Q

What is the innermost tunic

A

Retina

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2
Q

What happens to light at the retina

A

Light energy is transformed into a neural signal (phototransuction)

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3
Q

Where is the phototransduction signal modified

A

Within the retina

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4
Q

What part of the visual pathway is in the retina

A

Contains the first three cells of the pathway
Photoreceptors (1st)
Bipolar (2nd)
Ganglion (3rd)

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5
Q

What are the 9 inner layers of retina

A

Sensory or neural retina

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6
Q

What is the outermost retinal layer

A

RPE

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7
Q

Are all regions of the retina the same

A

No

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8
Q

What is in the outer retinal layers

A

Photoreceptor layer
External limiting membrane
Outer nuclear layer
Outer plexiform layer

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9
Q

What do photoreceptors span

A

The outer retina

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10
Q

What is contained in the photoreceptor layer

A

Rod outer segment
Rod inner segment
Cone outer segment
Cone inner segment

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11
Q

What is in the outer nuclear layer

A

Row of cone nuclei

Multiple rows or rod nuclei

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12
Q

What is in the outer plexiform layer

A

Contains rod spherules and cone pedicles

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13
Q

Role of photoreceptor

A

Absorb light photons and convert them into an electrochemical event though the process of phototransduction.

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14
Q

What are the two kinds of photoreceptors

A

Rods and cones

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15
Q

What part of the rod is adjacent to the RPE

A

Outer segment

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16
Q

What is the bridge between the outer segment and the inner segment of the rod

A

Cilium

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17
Q

What part of the rod photoreceptor goes through the external limiting membrane

A

Outer fiber

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18
Q

What is contained in the outer segment of the rods

A

Plasma membrane with discs containing rhodopsin

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19
Q

What is contained in the inner segment of the rod photoreceptor

A

Mitochondria and RER and Golgi

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20
Q

Photopigment of the rod

A

Rhodopsin

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21
Q

Where is rhodopsin located

A

In the membrane of the discs and to a lesser extent in the cell membrane around the cell body

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22
Q

What is rhodopsin composed of

A

Protein part, opsin, and chromosphere 11-cigs retinal (vit A derivative)

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23
Q

What is the peak absorption of light in rhodopsin

A

500nm (blue-green light), allows black and white

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24
Q

How are the photoreceptors and the RPE situated together

A

Apex to apex

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25
Q

When are rod outer segment discs shed?

A

In the early morning

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26
Q

How do the discs of the rods get engulfed

A

The engulfed discs become phagocytes in the RPE and are broken down by lysis
Or goes to drusen in the outer membrane

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27
Q

What is the turnover of the entire rod outer segment

A

About 2 weeks

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28
Q

What causes retinitis pigmentosa

A

Over 100 mutations in the rhodopsin gene have been IDed that can lead to inheritance of the rod photoreceptor dystrophy

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29
Q

What kind of disorder is retinitis pigmentosa

A

A progressive degeneration of rod photoreceptors

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30
Q

When does retinitis pigmentosa manifest

A

In the second to third decade of life

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31
Q

Where does retinitis pigmentosa being

A

In the mid peripheral retina leaving only a small island of surviving cone photoreceptors in the macula

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32
Q

What is the chief complaint of someone with retinitis pigmentosa

A

Difficulty with night vision, especially driving.

Patients with this complaint already have significant loss of rod photoreceptors and retinal function

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33
Q

Is there inflammation involved in retinitis pigmentosa

A

No

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34
Q

What kind of vision does someone with retinitis pigmentosa have

A

Tunnel vision

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35
Q

What is a characteristic feature of the retina in retinitis pigmentosa

A

Bone spicules

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36
Q

What happens in RP

A

Lows down pigment around BV and blocks them. BV supporting inner retina causes pallor in ONH

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37
Q

Serves as a bridge between the rod outer and inner segment

A

Connecting cilium

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38
Q

What is the arrangement of the connecting cilium

A

9+0 arrangement of doublets of microtubules

It’s missing the central pair of microtubules usually present in the motile cilia

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39
Q

What is the purpose of the inner segment in the photoreceptors

A

Powerhouse and metabolic machinery

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40
Q

What are the two segments of the inner segment

A

Ellipsoid

Myoid

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41
Q

What is the ellipsoid region of the inner segment

A

Close to the rod outer segment and contains mitochondria

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42
Q

What is contained in the myoid region of the inner segment of the photoreceptor

A

Closer to the cell body of the rod

-contained the metabolic machinery (RER, Golgi) for synthesizing protein for new discs

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43
Q

Extends from the inner segment of the photoreceptor to the cell body

A

Outer fiber

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44
Q

Length of outer fiber of photoreceptors

A
  • varies in length based on position of the cell body within the outer nuclear layer
  • more inward located rod cell bodies have a longer outer fiber
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45
Q

Where are the cones situated as the outside row

A

Outside the fovea

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46
Q

The axon of the rod photoreceptor, contains microtubules and extends from the cell body to the pear shaped spherule in the OPL.

A

Inner fiber

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47
Q

Synaptic terminal of rod

A

Spherule

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48
Q

Which is closer to the ONL, cone pedicles or rod spherules

A

Rod spherules

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49
Q

What is contained in the rod spherule

A

Mitochondria, synaptic vesicles, and microtubules

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50
Q

What is the triad of the rod spherules

A

Processes from horizontal cells and dendrites from rod bipolar cells invaginate the spherules forming a triad.

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51
Q

How many triads are in the rod spherules

A

1

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52
Q

What does the rod spherule release

A

Glutamate

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53
Q

What is the triad

A

To horizontal cells plus a rod bipolar cell on the rod spherules

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54
Q

How many rods are there

A

92 to 120 mill

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55
Q

What do rods mediate

A

Vision in dimly lit (scotopic) environments

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56
Q

Vision produced by rods

A

Consists of varying shades of black and white

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57
Q

Photopigment of the rods

A

All contain the same photopigment, rhodopsin

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58
Q

Rod photoreceptor density peaks where

A

18 degrees from the center of hte fovea and forms a ring around the fovea

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59
Q

Where are there no rods

A

Fovea

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60
Q

Sensory structure of the cone photoreceptor responsible for capturing photons of light

A

Outer segment

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61
Q

Shape of the outer segment of the cone photoreceptor

A

Cone like

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62
Q

Appearence of the outer segment of the cone photoreceptors in the fovea

A

Appear more rod like due to the dense packing of cone photoreceptors

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63
Q

What is the difference between the discs in the cone outer segment and rod outer segment

A

In the cone outer segments they are actually invaginations of the plasma membrane, which means they are discs in contact with the extracellular environment

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64
Q

What are the cone opsins

A
  • S cones: blue wavelength 488nm
  • M cones: green wavelength 531nm
  • L cones: red wavelength 588nm
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65
Q

What opsin do most cones contain

A

Green cones (M cones)

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66
Q

What are the three cone mechanism a basis are

A

Trichromatic vision

67
Q

When one of the three cone photopigments is absent and color is reduced to two dimensions

A

Dichromacy

68
Q

What are the different dichromats

A

Protanopes (no L)
Dueteranopes (no M)
Tritanopes (no S)

69
Q

This occurs when one of the cone photopigments is altered in its spectral sensitivity

A

Anomalous trichromacy

70
Q

Severe difficulty discriminating red green hues

A

Protonomaly

71
Q

Mildly affected red green hue discrimination

A

Deuteronomy

72
Q

Difficulty discriminating blue green and yellow/red-pink

A

Tritanomaly

73
Q

Connecting cilium in the cone versus in the rod

74
Q

Inner segment of the cone photoreceptor

A

Same basic structure as the rod photoreceptor. However, the ellipsoid region of the cone if much broader and contains a greater absolute number of mitochondria

75
Q

What is the difference between inner segment of the cone vs the rod

A

The ellipsoid region of the cone is much broader and contains a greater absolute number of mitochondria

76
Q

Outer fiber of the cone photoreceptor

A

Very short and sometimes absent. When absent the inner segment connects directly to the cone cell body

77
Q

Cone cell bodies

A

Monolayer of nuclei in the outermost row of the ONL. However, because there are no rod photoreceptors in the fovea, cone nuclei occupy all the rows of the ONL

78
Q

Which have larger nuclei, rods or cones?

79
Q

Appearance of cone nuclei versus rod nuclei

A

Cone nuclei appear paler than rod nuclei due to less heterochromatin

80
Q

The axon of the cone photoreceptor

A

Inner fiber

81
Q

Contains microtubules and extends from the cell body to the pedicle in the OPL

A

Inner fiber of the cone photoreceptor

82
Q

How are the cone inner fibers situated outside the fovea

A

Oriented vertically in the OPL

83
Q

How are inner fiber of the cone photoreceptor oriented in the fovea

A

The cone inner fiber is oriented obliquely due to lateral displacement of the inner retinal layers

84
Q

What are the obliquely displaced inner segments of the cone segments in the fovea called

A

Henle fibers. OPL in the fovea is often referred to as Henles fiber layer

85
Q

Pedicle of the cone vs spherule of the rod

A

Pedicle is larger and lie further from the ONL as compared to the rod spherules

86
Q

What the does pedicle of the cone contain

A

Mitochondria, clear synaptic vesicles, and microtubules

87
Q

What forms the triad in the cone pedicle

A

Processes from horizontal cells and dendrites from invaginating midget cone bipolar cells

88
Q

How many triads does a cone pedicle have

A

As many as 30 triads (and 30 ribbons)

89
Q

What is the NT released by the cone photoreceptors

90
Q

How many cones are there

91
Q

What percentage of cones are in the fovea

92
Q

Cones mediate what kind of vision

A

Brightly lit (photopic) environments

93
Q

Cone driven vision is responsible for __________

A

Color vision and sharp acuity

94
Q

Cell bodies of the interneurons

A
  • horizontal cells
  • rod and cone bipolar cells
  • amacrine cells
  • interplexiform cells
  • muller cells
95
Q

These modulate the signal from photoreceptors to bipolar cells and provide inhibitory feedback to photoreceptors and inhibitory feed-forward to bipolar cells

A

Horizontal cells

96
Q

Where are horizontal cells found

A

Outermost row of INL (monolayer)

97
Q

Make up of horizontal cells

A

Long axons and several dendritic processes that extend parallel to the retinal surface and terminate exclusively in the OPL

98
Q

Where do the dendritic processes of the horizontal cells terminate

A

Exclusively in the OPL

99
Q

What are the 3 types of horizontal cells

A

HI. HII. And HIII

100
Q

Horizontal cells in the triad

A

Horizontal cell dendritic processes flank the central bipolar dendrite in the triad

101
Q

What kind of NT do horizontal cells release

A

Inhibitory NT GABA

102
Q

What does GABA released by horizontal cells do

A

Inhibits activity of distant bipolar cells to sharpen contrast and enhance spatial resolution

103
Q

How do horizontal cells communicate with each other

A

Gap junctions

104
Q

Second neuron in the chain between the photoreceptors and the retinal ganglion cells

A

Retinal bipolar cells

105
Q

Bridge connecting outer to the inner retina

A

Retinal bipolar cells

106
Q

How many retinal bipolar cells are there

107
Q

Where are the nuclei of the retinal bipolar cells located

A

In any of the rows of the INL

108
Q

Where do the retinal bipolar cell dendrites extend

A

Into the OPL and synapse with photoreceptors and horizontal cells

109
Q

Where do the axons of the retinal bipolar cells go

A

Synapse with ganglion cells and amacrine cells in the IPL

110
Q

What are the two basic types of retinal bipolar cells

A

Rod bipolar cells and cone bipolar cells

111
Q

These bipolar cells contact only rod photoreceptors and synapse with the spherule in the OPL

A

Rod bipolar cells

112
Q

Where do rod bipolar cells begin to appear

A

In the parafovea and are Preston out to the far peripheral retina

113
Q

Axons of the rod bipolar cell

A

Extends into the IPL and will form a synaptic terminal called a dyad

114
Q

Dyad of rod bipolar cells

A

Contact a pair of AMA Rinne cell processes in sub lamina B (ON sublayer) in the IPL

115
Q

NT released from rod bipolar cells

116
Q

These contact only cone receptors in the OPL

A

Cone bipolar cells

117
Q

How many subtypes of cone bipolar cells are there

A

12 different

118
Q

What are the cone bipolar cells categorized based on

A

Polarity of their response to light as either ON bipolar or OFF bipolar

119
Q

ON cone bipolar cells

A

Axons will synapse with dendrites of ganglion cells in sublamina B (ON layer) in the IPL

120
Q

OFF cone bipolar cells

A

Synapse with dendrites of OFF ganglion cells in sublamina A (OFF sublayer)

121
Q

NT released by cone bipolar cells

122
Q

Do the rods have ON and OFF pathways?

A

No everthing is ON

123
Q

Where are the nuclei of the amacrine cells located

A

Innermost layer of the INL and sometimes in the GCL or IPL

124
Q

Different types of amacrine cells

A

There are many different types that vary greatly in their morphology and neurochemistry

125
Q

What do amacrine cells do

A

Modify signals in the IPL

126
Q

Axons of the amacrine cells

A

Typically do not have axons, however they have a single processes that has extensive branches and exhibits characteristics of both dendrites and axons

127
Q

What amacrine cell processes synapse with

A

Processes of other amacrine cells, bipolar cells, interplexiform cells, and retinal ganglion cells in the IPL

128
Q

What are the different groups of amacrine cells

A
  • narrow field
  • small field
  • medium field
  • wide field

May also be described as stratified or diffuse depending upon the distribution of their processes in the IPL

129
Q

What do 40% of amacrine cells contain (NT)

A

Glycine and GABA

Both inhibitory

130
Q

What is the most widely studied amacrine cell in the retina

A

Narrow field AII amacrine cell

131
Q

Convey the rod signal to the retinal ganglion cells as rod photoreceptors have no direct contact with retinal ganglion cells

A

AII amacrine cells

132
Q

Each AII amacrine cell may transmit from as many as ____ rod photoreceptors

133
Q

Wiring of amacrine cells

A

All amacrine cell transmits the rod signal from the rod bipolar cell to the either an ON cone bipolar cell via a gap junction (electrical synapse, sign conserving) or an OFF cone bipolar via a glycinergic synapse (inhibitory, sign inverting)

134
Q

Nuclei of interplexifom cells

A

Interspersed with the amacrine cells in the innermost layer of the INL

135
Q

Where do the interplexiform cells send their processes

A

To both the OPL and IPL, which carry feedback signals between the two layers

136
Q

What NT does interplexifrom cells release

A

GABA or dopamine

Inhibitory

137
Q

What are the 3 types of glial cells

A

Muller cells
Astrocytes
Microglia

138
Q

What are the radial glial cells of the retina

A

Muller cells

139
Q

These provide structural support, regulate concentrations of K+ and glutamate in the extracellular environment, synthesize and store glycogen, and are proliferate in response to pathological processes in the retina

A

Muller cells

140
Q

Where are the nuclei of the muller cells located

141
Q

Distal and proximal processes of the muller cells

A

Span from the ELM to the ILM

142
Q

Apical end of the distal process of the muller cell

A

Located in the PRL and consists of microvilli (fiber baskets of Schultze) that extend between the inner segments of hte photreceptos increasing the surface area for absorption of metabolites

143
Q

Basilar end of the proximal processes of muller cells

A

Consists of endfoot that contributes to the formation of ILM

144
Q

What attaches adjacent distal processes of muller cells, and muller cells to photoreceptors, whihc form the ELM

A

Zonula adherens

145
Q

Found in the RNFL and RGCL, send out processes that surround and provide structural support to the vasculature and axons located in the RNFL

A

Astrocytes

146
Q

Found in small numbers in the RNFL, mobile phagocytes that become highly active and can be found anywhere in the retina under pathological conditions

147
Q

What is the IPL divided into

A 
Sublamina A (OFF)
Sublamina B (ON)
148
Q

What is sublamina A (OFF) of the IPL further divided into

A

Sublamina S1 and S2

149
Q

What is sublamina B (ON) of the IPL further divided into

150
Q

Where in the IPL do the rod bipolar cells have to synapse

A

Sublamina B (usually S5)

151
Q

How many retinal ganglion cells reside in the retinal ganglion layer

A

1.2 to 2.2 mill

152
Q

Output cells of the retina that convey all of the processed visual information to the brain

A

Retinal ganglion cells

153
Q

Dendrites of the retinal ganglion cells

A

Ramify with processes of interneurons in the IPL

154
Q

Axons of the retinal ganglion cells

A

Form the RNFL, whihc ultimately gives rise to the optic nerve

155
Q

Are retinal ganglion cells bipolar or multipolar/

A

Can be either

156
Q

NT of retinal ganglion cells

157
Q

Classification of retinal ganglion cells

A

Based on the layer of the lateral geniculate body in which they synapse. Classified as parvocellular (P cells) or magnocellular (M cells)

158
Q

80% of the retinal ganglion cell population. A single dendrite projection into the IPL and synapse with a midget cone bipolar cell, which means the information conveyed to this type of cell is from a single cone photoreceptor. This arrangement allows for conveyance of information related to color and high resolution

159
Q

Another name for P cells

A

Midget bipolar cells

160
Q

10% of the retinal ganglion cell population. They have a larger cell body relative to the P cells. The dendrites of these cells arborize extensively in the IPL. They have wide dendritic fields that allow them to cover the entire retina. Respond to moving or changing stimuli in the environment

161
Q

Where do the other 10% of retinal ganglion cells that are not classified as P cells or M cells go

A

Connect to the superior colliculi

162
Q

Composed of unmyelinated axons od retinal ganglion cells. Also contains the superficial capillary plexus of the retinal vasculature. The axonal fibers course parallel to the retinal surface in an orderly fashion towards the central retina where they will converge to form the optic disc

A

Retinal nerve fiber layer (RNFL)

163
Q

What is the ILM formed by

A

The basement membrane of the endfeet of the muller cells

Ocular Block 7 (9 decks)

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