Lecture 9: Retina Flashcards
1
Q
how many layers does the retina have?
A
10
2
Q
what are 2 divisions of the retina
A
sensory and neural
3
Q
what is the 10th outermost layer?
A
retinal pigment epithelium (RPE)
4
Q
what are the 7 cells in the retina
A
- photoreceptors
- horizontal cells
- bipolar cells
- amacrine cells
- interplexiform cells
- ganglion cells
- Müller cells
5
Q
what are the 10 layers of the retina?
A
- Internal limiting membrane (ILM)
- Nerve fiber layer (NFL)
- Ganglion cell layer (GCL)
- Inner plexiform layer (IPL)
- Inner nuclear layer (INL)
- Outer plexiform layer (OPL)
- Outer nuclear layer (ONL)
- External limiting membrane (ELM)
- Photoreceptor layer (PR)
- Retinal Pigmented epithelium (RPE)
6
Q
what are the 5 RPE functions?
A
- Absorption of stray light
- Protection against toxic and oxidative damage
- Formation of blood-retina-barrier
- Selective transport of substances to and from the retina
- Elimination of metabolic waste
7
Q
Monolayer of polarized cuboidal cells separate what?
A
photoreceptors from their underlying blood supply (choroid)
8
Q
The PR layers contain what?
A
the outermost portion of photoreceptors, the portion containing the photopigment.
9
Q
PRS are specialized cells that do what?
A
convert light energy into a neural message (phototransduction).
10
Q
The outer portions of the PRs are adapted for what?
A
capturing light, while their inner parts are for transmitting the signal.
11
Q
what are two types of PRs?
A
rods and cones
12
Q
what are 7 parts common to PRs
A
- Synaptic terminal
- Inner Fiber
- Cell body
- Outer Fiber
- Inner Segment (IS)
- Cilium (Connecting Stalk)
- Outer Segment (OS)
13
Q
Outer Segment (OS)
A
Stack of membranous discs with photopigment in the membrane of the discs and plasma membrane of the cell.
14
Q
what are the areas called inside and outside discs?
A
The area inside of the disc is called the intradiscal space, the area between the disc is the extra disc space
15
Q
what structures are at the apical end of the RPE and project between the outer segments of the rods?
A
microvilli
16
Q
Cilium (connecting stalk)
A
Act to move OS towards direct path of light
17
Q
inner segment consists of what?
A
– ellipsoid region (mitochondria) near the cilium
– myoid region (endoplasmic reticulum & golgi apparatus) near outer fiber
18
Q
The inner fiber is the what of the photoreceptor.
A
axon
19
Q
the axon extends from where and forms what?
A
Extends from cell body and forms specialized ending, the synaptic terminal
20
Q
how many rods are there?
A
92-120 million rods
21
Q
are rods specialized for light or dark?
A
dark: Dim light vision (scotopic)
22
Q
where is rhodopsin located?
A
disc membrane
23
Q
where is rod peak density?
A
in a ring 4.5 mm
outside the fovea
24
Q
T/F: THERE ARE NO RODS IN THE FOVEA
A
T
25
rod outer segment contains how many discs?
600-1000 discs
26
Each disc membrane is separate
| from the plasma membrane, except where?
at the base where the intradisc space is continuous with the extracellular space
27
how many cones are there?
5-6 million cones
28
are cones specialized for light or dark?
light: Bright illumination (photopic) and color
29
the disc membrane contains what and are sensitive to what?
Contain 1 of 3 photo pigments (conopsins)
| stored in the disc membrane that are sensitive to different wavelengths of light
30
T/F: Cone OS is longer and more stout than those of rods
F: Cone OS is shorter and more stout than those of rods
31
Cones discs are shed at end of day and are phagocytosed by what?
RPE
32
OS of cones are enclosed by and continuous with?
Outer segment of cones is enclosed by Plasmalemma as in Rods but it is continuous with membrane forming most discs.
33
PR Synaptic Terminals: Rods inner fibers give way to what?
Inner fibers give way to a spherule (synapses with rod bipolar cell & process of horizontal cell)
34
PR Synaptic Terminals: Cones inner fibers give way to what?
Inner fibers give way to pedicle (synapses with several interneurons)
35
when are rod discs shed?
in the early morning
36
when are cone discs shed?
during the evening
37
discs are phagocytosed by?
RPE
38
The external limiting membrane lies next to what?
the outer edge of the outer nuclear layer.
39
zonula adherens are between what two cells?
PRs and Muller Cells
40
the external limiting membrane acts as a barrier to what?
the passage of large molecules
41
rods and cone cell bodies are contained where
the external limiting membrane
42
cone cell bodies lie in a single layer close to what?
external limiting membrane
43
Cell bodies of Rods are arranged how?
in several rows inner to cone cell body
44
ONL is thickest in the Fovea - how many layers of cone nuclei
10
45
The outer plexiform layer (OPL) can be thought of as having 2 layers:
1. a wide outer band
| 2. thinner inner band
46
A wide outer band composed of
the inner fibers (aka Henle’s fibers) of the rods and cones
47
A thinner inner band made up of
the synaptic terminals of photoreceptors, dendrites of bipolar cells, as well as horizontal cell axons and dendrites
48
where do the synaptic terminals synapse with the dendrites of bipolar and horizontal cells
Outer plexiform layer
49
The outer plexiform layer is where the photoreceptor cells make their synaptic connections
bipolar cells
50
The inner retina is supplied by
Retinal vasculature
51
the outer retina is supplied by
choroid
52
what layer marks the deepest penetration of blood vessels from the central retinal vasculature
inner nuclear layer
53
The inner nuclear layer contains nuclei of 5 basic types of neural cells - what are they?
1. amacrine cells
2. horizontal cells
3. bipolar cells
4. muller cells
5. interplexiform cells
54
amacrine cells:
intermediate synaptic connections between the bipolar and ganglion cells (transfer signal parallel).
55
horizontal cells:
intermediate synaptic connection between bipolar and photoreceptor cells.
56
Bipolar cells:
Dendrites synapses with PR and horizontal cells, Axon synapses with ganglion and amacrine cells
57
Muller cells:
extends throughout retinal layers, supportive role and structure.
58
Interplexiform cells:
synapse to Amacrine cells and bipolar cells, provide feedback from inner to outer layers of retina
59
what layer is composed of the dendrites of the retinal ganglion cells and the axons of bipolar cells
the inner plexiform layer
60
The inner plexiform layer is where the bipolar cells make their synaptic connections with
ganglion cells
61
This layer is generally one cell thick, but near the macula the layers pile up.
Ganglion Cell Layer
62
Retinal Ganglion cells are the output cells of the retina that communicate with
the central visual system structures.
63
The retinal ganglion cells are the primary cells affected in
glaucoma
64
The ganglion cells layer contains the cell bodies of
ganglion cells
65
The nerve fiber layer is made up of
unmyelinated fibers (do not aquire myelination until the axons pass through the lamina cribrosa)
66
does the nerve fiber layer increase or decrease one moves towards the optic nerve head
increase
67
in the NFL all fibers exit where?
All the fibers exit at the optic disc, thus it is thicker there.
68
The central retinal vessels are located primarily in
NFL/GCL
69
The ganglion cell to photoreceptor in the macular region is almost
1:1
70
T/F: Moving outward from the macular the ratio changes with one ganglion cell representing input from many photoreceptors.
T
71
what layer is the most vitread of all the retinal layers?
internal limiting membrane
72
internal limiting membrane is formed by
footplates of Muller cells, which are covered by a basement membrane.
73
Anteriorly, the ILM of the retina is continuous with
the ILM of the covering the ciliary body
74
posteriorly, at the optic disc, footplates of Muller cells are replaced by
astrocytes that form the ILM of the optic disc.
75
Müller cells are long glial cells that extend
from the ILM to just below the ELM
76
Müller cells provide what
support and maintain extracellular environment
77
Central retina is designed for
high visual acuity
78
the central retina has certain what
structural modifications from the peripheral retina
79
the central retina contains
1. Macula
2. Fovea
3. Foveola
80
how big is the macula?
Macula is 5.5 mm diameter
81
how big is the center of the macula and where is it located?
Its center is 3.5 mm lateral to the temporal edge of the optic disc and 1 mm below the center of the disc
82
why does the macula appear dark?
Appears dark due to the change in RPE morphology (taller and contain more pigment)
83
why is yellow hue often observed due to
increased amounts of Xanthophyll (lutein and zexanthin) in the ganglion and bipolar cells: Antioxidant, UV protection
84
what is a distinguishing feature of the macula
presence of an intraretinal pigment – xanthophyll
85
what portion of the retina provides the best visual acuity
fovea
86
are rods or cones found in the fovea
only cones
87
how big is the fovea?
1.5 mm diameter
88
clivus:
Walls slope downward toward the foveola
89
is the fovea vascular or avascular
avascular
90
what layers are present in the fovea
Only outer retinal layers are present
91
The OS of the cones are elongated for
maximizing packing density (150,000 - 300,000 cone cells/mm2)
92
The inner fibers of photoreceptors found in the outer plexiform layer are horizontally or vertically
oriented
horizontally oriented (vertical elsewhere in the retina).
93
the horizontally orientated layer is referred to as
Nerve Fiber Layer of Henle
94
The layers of the fovea are dependent upon
the underlying RPE and choriocapillaries for their metabolic support
95
foveola
Center of the fovea
96
how big is the foveola
.35 mm in diameter
97
what is present in the foveola
* Cone concentration is highest here
* Only outer retinal layers present
* Foveal reflex
