Retinal Histology Flashcards
1
Q
What is the innermost tunic
A
Retina
2
Q
What happens to light at the retina
A
Light energy is transformed into a neural signal (phototransuction)
3
Q
Where is the phototransduction signal modified
A
Within the retina
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)
5
Q
What are the 9 inner layers of retina
A
Sensory or neural retina
6
Q
What is the outermost retinal layer
A
RPE
7
Q
Are all regions of the retina the same
A
No
8
Q
What is in the outer retinal layers
A
Photoreceptor layer
External limiting membrane
Outer nuclear layer
Outer plexiform layer
9
Q
What do photoreceptors span
A
The outer retina
10
Q
What is contained in the photoreceptor layer
A
Rod outer segment
Rod inner segment
Cone outer segment
Cone inner segment
11
Q
What is in the outer nuclear layer
A
Row of cone nuclei
Multiple rows or rod nuclei
12
Q
What is in the outer plexiform layer
A
Contains rod spherules and cone pedicles
13
Q
Role of photoreceptor
A
Absorb light photons and convert them into an electrochemical event though the process of phototransduction.
14
Q
What are the two kinds of photoreceptors
A
Rods and cones
15
Q
What part of the rod is adjacent to the RPE
A
Outer segment
16
Q
What is the bridge between the outer segment and the inner segment of the rod
A
Cilium
17
Q
What part of the rod photoreceptor goes through the external limiting membrane
A
Outer fiber
18
Q
What is contained in the outer segment of the rods
A
Plasma membrane with discs containing rhodopsin
19
Q
What is contained in the inner segment of the rod photoreceptor
A
Mitochondria and RER and Golgi
20
Q
Photopigment of the rod
A
Rhodopsin
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
22
Q
What is rhodopsin composed of
A
Protein part, opsin, and chromosphere 11-cigs retinal (vit A derivative)
23
Q
What is the peak absorption of light in rhodopsin
A
500nm (blue-green light), allows black and white
24
Q
How are the photoreceptors and the RPE situated together
A
Apex to apex
25
When are rod outer segment discs shed?
In the early morning
26
How do the discs of the rods get engulfed
The engulfed discs become phagocytes in the RPE and are broken down by lysis
Or goes to drusen in the outer membrane
27
What is the turnover of the entire rod outer segment
About 2 weeks
28
What causes retinitis pigmentosa
Over 100 mutations in the rhodopsin gene have been IDed that can lead to inheritance of the rod photoreceptor dystrophy
29
What kind of disorder is retinitis pigmentosa
A progressive degeneration of rod photoreceptors
30
When does retinitis pigmentosa manifest
In the second to third decade of life
31
Where does retinitis pigmentosa being
In the mid peripheral retina leaving only a small island of surviving cone photoreceptors in the macula
32
What is the chief complaint of someone with retinitis pigmentosa
Difficulty with night vision, especially driving.
Patients with this complaint already have significant loss of rod photoreceptors and retinal function
33
Is there inflammation involved in retinitis pigmentosa
No
34
What kind of vision does someone with retinitis pigmentosa have
Tunnel vision
35
What is a characteristic feature of the retina in retinitis pigmentosa
Bone spicules
36
What happens in RP
Lows down pigment around BV and blocks them. BV supporting inner retina causes pallor in ONH
37
Serves as a bridge between the rod outer and inner segment
Connecting cilium
38
What is the arrangement of the connecting cilium
9+0 arrangement of doublets of microtubules
It's missing the central pair of microtubules usually present in the motile cilia
39
What is the purpose of the inner segment in the photoreceptors
Powerhouse and metabolic machinery
40
What are the two segments of the inner segment
Ellipsoid
| Myoid
41
What is the ellipsoid region of the inner segment
Close to the rod outer segment and contains mitochondria
42
What is contained in the myoid region of the inner segment of the photoreceptor
Closer to the cell body of the rod
| -contained the metabolic machinery (RER, Golgi) for synthesizing protein for new discs
43
Extends from the inner segment of the photoreceptor to the cell body
Outer fiber
44
Length of outer fiber of photoreceptors
- 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
45
Where are the cones situated as the outside row
Outside the fovea
46
The axon of the rod photoreceptor, contains microtubules and extends from the cell body to the pear shaped spherule in the OPL.
Inner fiber
47
Synaptic terminal of rod
Spherule
48
Which is closer to the ONL, cone pedicles or rod spherules
Rod spherules
49
What is contained in the rod spherule
Mitochondria, synaptic vesicles, and microtubules
50
What is the triad of the rod spherules
Processes from horizontal cells and dendrites from rod bipolar cells invaginate the spherules forming a triad.
51
How many triads are in the rod spherules
1
52
What does the rod spherule release
Glutamate
53
What is the triad
To horizontal cells plus a rod bipolar cell on the rod spherules
54
How many rods are there
92 to 120 mill
55
What do rods mediate
Vision in dimly lit (scotopic) environments
56
Vision produced by rods
Consists of varying shades of black and white
57
Photopigment of the rods
All contain the same photopigment, rhodopsin
58
Rod photoreceptor density peaks where
18 degrees from the center of hte fovea and forms a ring around the fovea
59
Where are there no rods
Fovea
60
Sensory structure of the cone photoreceptor responsible for capturing photons of light
Outer segment
61
Shape of the outer segment of the cone photoreceptor
Cone like
62
Appearence of the outer segment of the cone photoreceptors in the fovea
Appear more rod like due to the dense packing of cone photoreceptors
63
What is the difference between the discs in the cone outer segment and rod outer segment
In the cone outer segments they are actually invaginations of the plasma membrane, which means they are discs in contact with the extracellular environment
64
What are the cone opsins
- S cones: blue wavelength 488nm
- M cones: green wavelength 531nm
- L cones: red wavelength 588nm
65
What opsin do most cones contain
Green cones (M cones)
66
What are the three cone mechanism a basis are
Trichromatic vision
67
When one of the three cone photopigments is absent and color is reduced to two dimensions
Dichromacy
68
What are the different dichromats
Protanopes (no L)
Dueteranopes (no M)
Tritanopes (no S)
69
This occurs when one of the cone photopigments is altered in its spectral sensitivity
Anomalous trichromacy
70
Severe difficulty discriminating red green hues
Protonomaly
71
Mildly affected red green hue discrimination
Deuteronomy
72
Difficulty discriminating blue green and yellow/red-pink
Tritanomaly
73
Connecting cilium in the cone versus in the rod
Similar
74
Inner segment of the cone photoreceptor
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
What is the difference between inner segment of the cone vs the rod
The ellipsoid region of the cone is much broader and contains a greater absolute number of mitochondria
76
Outer fiber of the cone photoreceptor
Very short and sometimes absent. When absent the inner segment connects directly to the cone cell body
77
Cone cell bodies
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
Which have larger nuclei, rods or cones?
Cones
79
Appearance of cone nuclei versus rod nuclei
Cone nuclei appear paler than rod nuclei due to less heterochromatin
80
The axon of the cone photoreceptor
Inner fiber
81
Contains microtubules and extends from the cell body to the pedicle in the OPL
Inner fiber of the cone photoreceptor
82
How are the cone inner fibers situated outside the fovea
Oriented vertically in the OPL
83
How are inner fiber of the cone photoreceptor oriented in the fovea
The cone inner fiber is oriented obliquely due to lateral displacement of the inner retinal layers
84
What are the obliquely displaced inner segments of the cone segments in the fovea called
Henle fibers. OPL in the fovea is often referred to as Henles fiber layer
85
Pedicle of the cone vs spherule of the rod
Pedicle is larger and lie further from the ONL as compared to the rod spherules
86
What the does pedicle of the cone contain
Mitochondria, clear synaptic vesicles, and microtubules
87
What forms the triad in the cone pedicle
Processes from horizontal cells and dendrites from invaginating midget cone bipolar cells
88
How many triads does a cone pedicle have
As many as 30 triads (and 30 ribbons)
89
What is the NT released by the cone photoreceptors
Glutamate
90
How many cones are there
5-6 mil
91
What percentage of cones are in the fovea
10%
92
Cones mediate what kind of vision
Brightly lit (photopic) environments
93
Cone driven vision is responsible for __________
Color vision and sharp acuity
94
Cell bodies of the interneurons
- horizontal cells
- rod and cone bipolar cells
- amacrine cells
- interplexiform cells
- muller cells
95
These modulate the signal from photoreceptors to bipolar cells and provide inhibitory feedback to photoreceptors and inhibitory feed-forward to bipolar cells
Horizontal cells
96
Where are horizontal cells found
Outermost row of INL (monolayer)
97
Make up of horizontal cells
Long axons and several dendritic processes that extend parallel to the retinal surface and terminate exclusively in the OPL
98
Where do the dendritic processes of the horizontal cells terminate
Exclusively in the OPL
99
What are the 3 types of horizontal cells
HI. HII. And HIII
100
Horizontal cells in the triad
Horizontal cell dendritic processes flank the central bipolar dendrite in the triad
101
What kind of NT do horizontal cells release
Inhibitory NT GABA
102
What does GABA released by horizontal cells do
Inhibits activity of distant bipolar cells to sharpen contrast and enhance spatial resolution
103
How do horizontal cells communicate with each other
Gap junctions
104
Second neuron in the chain between the photoreceptors and the retinal ganglion cells
Retinal bipolar cells
105
Bridge connecting outer to the inner retina
Retinal bipolar cells
106
How many retinal bipolar cells are there
35 mil
107
Where are the nuclei of the retinal bipolar cells located
In any of the rows of the INL
108
Where do the retinal bipolar cell dendrites extend
Into the OPL and synapse with photoreceptors and horizontal cells
109
Where do the axons of the retinal bipolar cells go
Synapse with ganglion cells and amacrine cells in the IPL
110
What are the two basic types of retinal bipolar cells
Rod bipolar cells and cone bipolar cells
111
These bipolar cells contact only rod photoreceptors and synapse with the spherule in the OPL
Rod bipolar cells
112
Where do rod bipolar cells begin to appear
In the parafovea and are Preston out to the far peripheral retina
113
Axons of the rod bipolar cell
Extends into the IPL and will form a synaptic terminal called a dyad
114
Dyad of rod bipolar cells
Contact a pair of AMA Rinne cell processes in sub lamina B (ON sublayer) in the IPL
115
NT released from rod bipolar cells
Glutamate
116
These contact only cone receptors in the OPL
Cone bipolar cells
117
How many subtypes of cone bipolar cells are there
12 different
118
What are the cone bipolar cells categorized based on
Polarity of their response to light as either ON bipolar or OFF bipolar
119
ON cone bipolar cells
Axons will synapse with dendrites of ganglion cells in sublamina B (ON layer) in the IPL
120
OFF cone bipolar cells
Synapse with dendrites of OFF ganglion cells in sublamina A (OFF sublayer)
121
NT released by cone bipolar cells
Glutamate
122
Do the rods have ON and OFF pathways?
No everthing is ON
123
Where are the nuclei of the amacrine cells located
Innermost layer of the INL and sometimes in the GCL or IPL
124
Different types of amacrine cells
There are many different types that vary greatly in their morphology and neurochemistry
125
What do amacrine cells do
Modify signals in the IPL
126
Axons of the amacrine cells
Typically do not have axons, however they have a single processes that has extensive branches and exhibits characteristics of both dendrites and axons
127
What amacrine cell processes synapse with
Processes of other amacrine cells, bipolar cells, interplexiform cells, and retinal ganglion cells in the IPL
128
What are the different groups of amacrine cells
- 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
What do 40% of amacrine cells contain (NT)
Glycine and GABA
| Both inhibitory
130
What is the most widely studied amacrine cell in the retina
Narrow field AII amacrine cell
131
Convey the rod signal to the retinal ganglion cells as rod photoreceptors have no direct contact with retinal ganglion cells
AII amacrine cells
132
Each AII amacrine cell may transmit from as many as ____ rod photoreceptors
30
133
Wiring of amacrine cells
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
Nuclei of interplexifom cells
Interspersed with the amacrine cells in the innermost layer of the INL
135
Where do the interplexiform cells send their processes
To both the OPL and IPL, which carry feedback signals between the two layers
136
What NT does interplexifrom cells release
GABA or dopamine
| Inhibitory
137
What are the 3 types of glial cells
Muller cells
Astrocytes
Microglia
138
What are the radial glial cells of the retina
Muller cells
139
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
Muller cells
140
Where are the nuclei of the muller cells located
INL
141
Distal and proximal processes of the muller cells
Span from the ELM to the ILM
142
Apical end of the distal process of the muller cell
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
Basilar end of the proximal processes of muller cells
Consists of endfoot that contributes to the formation of ILM
144
What attaches adjacent distal processes of muller cells, and muller cells to photoreceptors, whihc form the ELM
Zonula adherens
145
Found in the RNFL and RGCL, send out processes that surround and provide structural support to the vasculature and axons located in the RNFL
Astrocytes
146
Found in small numbers in the RNFL, mobile phagocytes that become highly active and can be found anywhere in the retina under pathological conditions
Microglia
147
What is the IPL divided into
```
Sublamina A (OFF)
Sublamina B (ON)
```
148
What is sublamina A (OFF) of the IPL further divided into
Sublamina S1 and S2
149
What is sublamina B (ON) of the IPL further divided into
S3-S5
150
Where in the IPL do the rod bipolar cells have to synapse
Sublamina B (usually S5)
151
How many retinal ganglion cells reside in the retinal ganglion layer
1.2 to 2.2 mill
152
Output cells of the retina that convey all of the processed visual information to the brain
Retinal ganglion cells
153
Dendrites of the retinal ganglion cells
Ramify with processes of interneurons in the IPL
154
Axons of the retinal ganglion cells
Form the RNFL, whihc ultimately gives rise to the optic nerve
155
Are retinal ganglion cells bipolar or multipolar/
Can be either
156
NT of retinal ganglion cells
Glutamate
157
Classification of retinal ganglion cells
Based on the layer of the lateral geniculate body in which they synapse. Classified as parvocellular (P cells) or magnocellular (M cells)
158
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
P cells
159
Another name for P cells
Midget bipolar cells
160
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
M cells
161
Where do the other 10% of retinal ganglion cells that are not classified as P cells or M cells go
Connect to the superior colliculi
162
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
Retinal nerve fiber layer (RNFL)
163
What is the ILM formed by
The basement membrane of the endfeet of the muller cells
