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Anatomy & Physiology 2 > Retina > Flashcards

Retina Flashcards

1
Q

How should the retina of a healthy subject look?

A

Healthy subject = transparent and looks purple-redish due to blood supply behind it.

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2
Q

How thick is the Retina?

A

The retina is a thin, transparent membrane having a purplish-red colour in living subjects. Its thickness varies from 0.56 mm near the optic disc to 0.1 mm at the ora serrata. It is thinnest at the centre of the fovea. The retina is continuous with the optic nerve posteriorly, and it extends forward to become the epithelium of the ciliary body and the iris.

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3
Q

Where & what is Bruch’s membrane?

A

Brunch’s membrane – between RPE and Vascular Choroid membrane. Bruch’s membrane is part of the choroid as it’s split into Bruch’s membrane and vascular membrane. Bruch’s membrane can be split into 5 layers – basement membrane (innermost layer; the retina sits on this) then there are 3 elastic layers and then have the basement membrane to the vascular layer of the choroid.

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4
Q

What’s the role of the retina?

A

Photochemical transduction occurs so that nerve impulses are created and transmitted along visual pathways to the brain for higher cortical processing.

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5
Q

Where is the retina firmly attached?

A

The retina is firmly attached at the margins of the optic disc and at its anterior termination at the ora serrata. It should be remembered that the retina extends more anteriorly on the medial side, so that the ora serrata lies closer to the limbus on that side. An approximate landmark on the outside of the eyeball is the point of insertion of the medial rectus muscle medially and the lateral rectus muscle laterally.

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6
Q

What is the ‘macula lutea’ and the ‘fovea centralis’?

A

At the centre of the posterior part of the retina is an oval, yellowish area, the macula lutea, which is the retinal area for the most distinct vision. It has a central depression, the fovea centralis

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7
Q

What is the ora-serrata?

A

The ora serrata is the serrated junction between the choroid and the ciliary body.

This junction marks the transition from the simple, non-photosensitive area of the ciliary body to the complex, multi-layered, photosensitive region of the retina.

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8
Q

What is Bruch’s membrane?

A

A structure comprising 5 layers, the most internal of which is the basement membrane of the RPE. The most external layer is the basement membrane of the choriocapillaris. The three middle layers can be thought of as elastic layers. Role is not fully understood.

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9
Q

What’s another name for the RPE/Pigmented Epithelial Cells?

A

Outer Pigmented Layer

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10
Q

What is the function of the RPE?

A

Function of the RPE
- Absorption of light (RPE stops return of light into the sensory layer of the retina)
– Turnover of the photoreceptor outer segments (rods and cones)
- Formation of rhodopsin and iodopisin by storing and releasing vitamin A (precursor)

Choroid removes debris and keeps photoreceptors clean. Age-Related Macular degeneration stops this occurring. Helps with turnover of photoreceptors outer segments debris.
Reason eyes don’t glow red when light comes in (due to light scattering) is that the RPE absorbs light and stops it scattering back into the eye.

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11
Q

Where does the RPE come from?

A
  • Single layer of cells
  • Comes from the outer layer of the optic cup (embryology)
  • Extend forward from the margin of the optic nerve to the ora serrata
  • From the ora serrata, the RPE continues as the pigmented layer of the ciliary epithelium
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12
Q

What are cells of the RPE like?

A
  • Cells are narrow and columnar, and become flatter as you progress anteriorly into the eye
  • Basal end rests on a basement membrane and is infolded
  • Apical end has microvilli which project between the rods and cones
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13
Q

How thick are RPE layers & what sit in the grooves?

A

RPE layer is 1 cell thick throughout the retina. Babysits the photoreceptors. Within folds in RPE cells are the photoreceptors; sitting in the little grooves. RPE cells are hexagonal organized.

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14
Q

What organelles are in the RPE?

A

Certain organelles in the RPE; mitrochondria (synthesis; active transport happening). Have rough and smooth ER (endoplasmic reticulum), Golgi apparatus. These three structures together suggest the cell is packaging something and getting rid of something. If you put loads together, to stop things leaking between them you have tight junctions (apical, towards retina, and basal, towards choroid).

Top/Apical - Zona Occludens

Bottom/Basal - Zona Adherans

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15
Q

How are the RPE cells bound to each other?

A

Adjacent RPE cells are bound basally by zonula adherans (nearest sclera/choroid) and apically by zonula occludens (nearest vitreous/retina). Together these binding sites eliminate any intracellular space.

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16
Q

How many Cones are there?

A

6 - 7 million

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17
Q

How many Rods are there?

A

120 million mainly in the periphery

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18
Q

What do the outer segment of Cones look like?

A

Cones have a cone shape in the outer segment of the cells. In cones in the disc this is called iodopsin and live on the membranes of the lamaelle.

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19
Q

What do the outer segment of Rods look like?

A

Rods have a rod shaped outer segment of the cell. In Rods photopgiments live on the lamaelle membranes but is called rhodopsin.

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20
Q

What is Iodopsin and Rhodopsin?

A

In the outer segments of rods and cones are lamaelle (sheets). Cone lamaelle membrane are in contact with the outside of the cells whereas rod lamaelle is contained within the cell. These contain photopigments that start off the phototransduction pathway.

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21
Q

How are the outer segments of the photoreceptors connected to the inner segments?

A

The outer segments link to inner segments by little corridors that are ciliary which help connect the two segments together

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22
Q

What can the Inner Segments of the photoreceptors be split into?

A

The inner segment can be split into two halves/sections.

Sections closest to outer segment of the cell is called the Elipsoid. The section of the inner segment closest to the inner part of the eye is the Myoid/Hyoid.

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23
Q

What organelles are in the myoid and Elipsoid regions of the photoreceptors?

A

Myoid region = Golgi and ER (endoplasmic reticulum) heavy

Elipsoid = Mitrochondria heavy

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24
Q

What’s below the inner segment of photoreceptors?

A

The cell body;
Below the inner segment of the rods and cones are the cell body which is the control centre of the cell.

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25
Where do the outer segments of photoreceptors sit?
In between the RPE
26
What is below the cell body of photoreceptors?
Below the cell body in the cone cells is the Cone Pedicle whereas in rod cells this is called the Rod Spherule At the ends of pedicles and spherules all that happens is that there are pre-synaptic vesicles and a synaptic cleft tor each a post-synaptic vesicle in the next retinal layer.
27
What are the sections of photoreceptor cells from outer to innermost?
Outer --> Inner - Iodopsin/Rhodopsin - Outer Segment - Inner Segment - Cell Body - Cone Pedicle/Rod Spherule
28
What do you know about Cone cells?
- Adapted for bright light and resolve fine details and colour vision. - 6–7 million cones in the retina and their density is concentrated in the fovea, - Discs containing iodopsin - Discs within the cone head which is the outer segment – Connecting stalk between outer segment and inner segment - Inner segment contains mitochondria in the ellipsoid region of inner segment - Inner segment contains golgi and ER in the myoid region of the inner segment - Inner segment connects to the cell body containing the nucleus – Cell body connects to the cone pedicle
29
What do you know about Rod cells?
- Approximately 120 million rods in the entire retina. There are no rods at the fovea and the number increases until the maximum density occurs in the juxtafoveal zone, - Discs containing rhodopsin. These discs are made at the base of the outer segment and pushed up the rod. Once at the top they are phagocytosed by the RPE – Connecting stalk between outer segment and inner segment - Inner segment contains mitochondria in the ellipsoid region of inner segment - Inner segment contains golgi and ER in the myoid region of the inner segment - Inner segment connects to the cell body containing the nucleus – Cell body connects to the rod spherule The spherule and pedicle contain presynaptic vesicles which synapse with dendrites of the bipolar cell
30
What are the types of bipolar cells?
- Rod Bipolar Cells - Flat Bipolar Cells - Midget Bipolar Cells
31
How many ganglion cells do Rod Bipolar Cells synapse with?
Synapse several rod cells to 1-4 ganglion cells
32
How many ganglion cells do Flat Bipolar Cells synapse with?
Synapse many cone cells with many ganglion cells
33
How many ganglion cells do Midget Bipolar Cells synapse with?
Single cone to single ganglion
34
What do photoreceptor cells synapse with after starting a nerve impulse?
Bipolar cells or Horizontal
35
What do Bipolar Cells look like?
Have 2 poles; cell body in middle. At the top and bottom you have dendrites to allow for transmission to the next layer (ganglion cell layer)
36
How are bipolar cells organised?
All in a radial fashion (in a circle going from middle outwards).
37
What is the function of bipolar cells?
Function is to synapse with photoreceptors to 2 cell types; ganglion and amacrine cells; either one or both.
38
What do bipolar cells synapse with?
Dendrites of the BP cells synapse with pedicle or spherule of R+Cs BP cells then synapse with ganglion and amacrine cells
39
What do Bipolar Cells synapse with on the inner side?
Ganglion Cells
40
What do Ganglion cells look like?
Resemble cells found in nervous system Ganglion cells look similar to neurons. Called this because they’re found in the brain (eyes and optic nerve are extension of the central nervous system). Approaching innermost part of the retina at this point.
41
How many cells thick are ganglion cells?
In the periphery these are single cell thick , approaching around macular up to around 10 layers. At the fovea the ganglion cells disappear. Fovea is just cone cells.
42
Regarding Ganglion Cells, where are they myelinated and where are they unmyelinated?
Once at the axon of this cell, up until the optic disc are unmyelinated but once they pass through the optic disc they become myelinated at the lamina cribrosa (once they leave the globe)
43
Are ganglion cells myelinated at the retina?
No - myelinated once they go pass the lamina cribrosa
44
Where is the mitrochondria of the ganglion cells densest?
Number of mitrochrondria in the axon is fewer in the myelinated section than the unmyelinated section (makes sense as the myelinated means less ATP is required so fewer mitrochondria needed).
45
What do Ganglion cells converge to form?
They converge to form the optic nerve that travels through the visual system.
46
How do ganglion cells reach the optic nerve?
They turn 90 degrees and turn back around dive to the optic nerve (the hole is the lamina cribrosa that contains central retinal artery, central retinal vein and optic nerve) as ganglion cells are more in the inner part of the eye. This is at the point they’re non-myelinated. Once at the optic disc is the lamina cribrosa where they become myelinated.
47
What is the Lamina Cribrosa?
The hole just before the optic disc is the lamina cribrosa that contains central retinal artery, central retinal vein and optic nerve. Ganglion cells pass through the sclera here. After they reach this point ganglion cells become myelinated.
48
What are the second order neurons in the visual pathway?
Ganglion Cells
49
What types of cells don't propagate through the retina (sclera to inner) but instead propagate within the layers?
Horizontal & Amacrine Cells
50
Where are Horizontal cells located?
Between the Pedicles and Spherule ends (between these and the BP cells)
51
How many poles do horizontal cells have?
They're multi-polar with more than 2 poles & made up of long and short processes
52
What do Horizontal cells synapse with?
They synapse between other rods and other cone cells. Long processes link rods and cones which are far away and also with bipolar cells .
53
How may Rods & Cones do Horizontal cells synapse with?
Horizontal cells can synapse with 10-20 rods Horizontal cells can synapse with 7 cones
54
What do Horizontal cells help us to see?
These help us to see peripheral light; peripheral rods and central rods start phototransduction process, this allows us to see the image as one rather than central and peripheral separately = transmit & combine the nerve impulses together. They’re max 1ml in size. Horizontal cells also make slight adjustments to the signals sent to the bipolar cells.
55
What are the functions of Horizontal cells?
Role: 1) Modulating signals between photoreceptors 2) Make slight adjustments to signals sent to bipolar cells
56
Where are Amacrine cells?
Close to where the ganglion cells synapse with the bipolar cells. Synapse with other ganglion and bipolar cells and modulate the activity moving between ganglion and bipolar cells. A bit like traffic lights to ensure impulse is moving at same speed across them (so images arrive at same time). Help to regulate already generated signals.
57
How do Amacrine cells look?
Amacrine cells have large cell bodies with lots of cytoplasm.
58
What do Amacrine cells synapse with?
Situated close to the ganglion cells and have long processes which radiate widely and synapse with other amacrine cells and dendrites of ganglion cells and bipolar cells
59
What are the roles of Amacrine cells?
They help to make sure that laterally placed ganglion cells are excited Also regulate activity between bipolar and ganglion cells
60
Where are Muller Cells?
Still spaces between all of the cells covered above and the body doesn’t like this so we have potential spaces.
61
What are Muller Cells designed for?
The Muller Cells are designed to support the retina but have no neural function (don’t transmit anything). They just stop all of the other cells flopping and collapsing and fill the spaces between the neural cells (bipolar cells, ganglion cells, photoreceptor cells). Like scaffolding. As they get to the ends of the long processes, as they get to inside of retina or towards sclera they spread out and mix themselves with a membrane which give us the inner and outer layers of the retina; formed by the terminal expansions of the Muller Cells. Like the bread of a sandwich. Have loads of expansions coming off of them, transparent and just fill all the gaps. Travel radially.
62
What forms the inner and outer limiting membranes?
As the muller cells approach the vitreous surface, the terminals expand and become covered with a basement membrane. This forms the inner limiting membrane.
63
What's the mnemonic to remember the retinal layers from INNER to OUTER layers?
In New Generations It Isn’t Only Ophthalmologists Examining Peoples Retinas This goes from Inner to Outer layers.
64
What are the 10 retinal layers?
1) Retinal Pigmented Epithelium (RPE) 2) Photoreceptor Layer 3) External Limiting Membrane 4) Outer Nuclear Layer 5) Outer Plexiform Layer 6) Inner Nuclear Layer 7) Inner Plexiform Layer 8) Ganglion Cell Layer 9) Nerve Fibre Layer 10) Inner Limiting Membrane
65
What makes up the photoreceptor layer?
Outer & Inner segments of the rods & cones
66
What is the external limiting membrane?
This is the line formed by junctional complexes between photoreceptor and Müller cells on the vitreous side
67
What makes up the outer nuclear layer?
Comprised of the cell bodies of the rods and cones (still quite scleral at this point)
68
What makes up the outer plexiform layer?
Dense collection of nerve cell processes from horizontal cells and bipolar cells (the arms of them not the bodies of the cell!) Plexiform = bunch of nerve fibres
69
What does the inner nuclear layer comprise of?
Inner nuclear layer comprised of cell bodies of horizontal cells, bipolar cells, amacrine cells and muller cells
70
What does the inner plexiform layer comprise of?
Dense collection of nerve cell processes (arms of them) of bipolar, amacrine and ganglion cells
71
What does the Ganglion fibre layer comprise of?
Comprises the bodies of ganglion cells. These ganglion cells serve as the last retinal integrator of information before leaving via the nerve fibres in the nerve fibre layer.
72
What does the Nerve Fibre Layer comprise of?
Processes of the ganglion cells converging towards the optic disc
73
What does the Inner Limiting Membrane comprise of?
The ILM (inner limiting membrane) and the ELM (external limited membrane) are both layers that are formed by the amalgamation of the inner and outer end processes of Müller cells, respectively.
74
How do we determine where the Macular starts?
To know where the macular is we’d have to do to histology. Where ganglion layer starts to become more than 1 cell thick --> 10 cells thick --> zero at the fovea centralis
75
How large is the macular?
The macula lutea (Latin for yellow) is an oval area at the posterior pole of the eye, roughly 3 mm lateral to the optic nerve head. Macular is roughly 4.5mm in diameter and around 3mm LATERAL to the optic disc.
76
How do we get central vision if there are only cones in the fovea centralis when there's no ganglion cells?
Under these are horizontal cells going over the dip that synapse to bipolar cells.
77
How big is the fovea?
The fovea is around 1.5mm in diameter and contains the most dense area of cone cells in the retina
78
What is the first branch of the ophthalmic artery?
Central Retinal Artery
79
Where does the central retinal artery travel?
- Pierces the optic nerve infero medially, around 12mm behind the globe - Once in the nerve, it has all 3 meningeal coverings - Pierces the eyeball and splits into the superior and inferior retinal arteries. SRA and IRA then split to each give off nasal and temporal branches - Venous drainage closely matches arterial supply - No lymph drainage
80
What layers of the retina are the central retinal artery in?
Nerve Fibre Layer to the Outer Plexiform Layer
81
What layers of the retina are the Choroidal Capillaries in?
Outer Plexiform Layer to the RPE
82
What layer of the retina has both the central retinal artery (CRA) and choroidal capillaries in?
Outer Plexiform Layer
83
Why do we get a cherry-red spot in central retinal artery occlusion?
Inner retina supplied by the central retinal artery (see central retinal artery occlusion as cherry red because we’d only be seeing the choroidal capillaries supplying). Really important for central retinal artery occlusion leading to lost vision is because the ganglion cell layer dies which takes signals to the optic nerve.
84
Why do we get cotton-wool spots in AMD?
RPE cells to remove debris of the rod and cone cells. In AMD they RPE doesn’t continue to do this cleaning as we get older. The debris (called Drusen) therefore builds up over time. Retina can also become hypoxic so look like cotton-wool spots that are stark white whereas drusen are yellowish. Tends to be more around the macular because we have a denser number of rods and cones in central vision. Can also happen around the optic disc (better as brain learns to ignore it)
85
How might central vein occlusion look on a fundus & media exam?
Central vein occlusion (stormy sunset appearance) – venous drainage of eye blocked, stayed in venous network so eventually blood seeps out of capillaries so this means that oxygen cannot get in as oxygenated blood cannot get through as venous blood is clogging it.
86
How does Diabetic Retinopathy look on a fundus & media exam?
Diabetic Retinopathy – high sugar levels cause haemorrhages and occlusions of the retina if uncontrolled. Cholesterol seeps out of blood and collects on the retina, get hypoxia (cotton-wool spots) and haemorrhages. Use laser to stop this (not macular, fovea or optic nerve) but will look like little holepunches in the eye.
87
Where does phototransduction occur?
Happens in the outer segment
88
Where is Rhodopsin and what is it a mixture of?
Membranes that contain Rhodopsin inside of the outer segment. Rhodopsin is a mixture of two substances being (membranes have 2 layers as a bi-layer and rhodopsin sits in the middle of this) opsin and retinal and goes between the top of one bilayer and the bottom of another bilayer. Opsin is this substance that does this and then retiNAL is inside of the opsin. It’s called cyst-retinal (same side of a double-bond) , in retinal there is a double carbon-carbon bond that’s on one side = cyst substance.
89
What type of channels are in the outer membrane disk of a Rod?
Sodium-potassium ATP channels
90
In the dark what happens to sodium-potassium channels in the outer membrane disk of Rods?
They're open in the dark
91
What is cyclic GmP and how does it work in the dark?
On the inside of the photoreceptors is cyclic-GmP which are always there but in the dark they bind to the ATP channels which is what keeps them open. This allows sodium and calcium (positive charge) to flood into the cell and for potassium to move out of the cell (negative)
92
What is the resting membrane potential of Rods in the dark?
Most cells exist in the –ve charge as a resting potential. Most cells in the dark sit around -45ve which keeps them depolarised.
93
What do Rod Spherules release in the dark?
From the transmitter at the bottom (spherule or pedicle) they release glutamate which is constantly being released when photoreceptors are in the dark which send signals to the brain
94
How does Phototransduction occur?
- When light comes in, the retiNAL in rhospsin absorbs a photon (light) which converts cyst-retiNAL to trans retiNAL. Which causes a cascade that cannot be stopped until the photoreceptors have to “reset” themselves. - Transducin is activated by the trans-retiNAL as it attaches itself to Rhodopsin which inactivates Rhodopsin. Transducin is attached to rhodopsin which takes it to another molecule that has been inactivate is called phosphodiesterase. - Once here at the Phosphodiesterase molecule it activates it which tells it to hydrolyse the cyclic-GmP (that in the dark has been keeping the channels open in the dark) it essentially turns it off and so cyclic-GmP levels drop (turns into a different type of molecule called GTP) which causes the closing of the sodium-potassium channels. - This causes Potassium levels to increase as they’re no longer leaving the cell. This causes the resting potential rate to decrease significantly to make the cell more negative than it previously was. - In rods when the potassium level goes up, the glutamate processes is lessened so they’re no longer sending a lot of signals to the brain.
95
What type of response is phototransduction?
This is all a graded response – more light hitting the retina = more it’s happening.
96
How many sodium-potassium channels are turned off with 1 retiNAL being stimulated?
When 1 retiNAL is switched from cyst to trans it induces 6 transducin and each of these act on ONE phosphodiesterase which can switch off around 10 GmP’s so for each retinal around 200 channels stop working in one rod cell.
97
How do photoreceptors stop firing at night?
Go through the day, then at night time to reset the photoreceptors they all have an automatic time-feature so they just end up stop doing what they’re doing aka. RetiNAL stops absorbing Rhodopsin stops activating transducin which cannot take it to phosphodiesterase so GmP goes back up.
98
What absorbs light in Rods?
Rhodopsin
99
How is Transducin activated?
By the Trans-RetiNAL
100
How is Phosphodiesterase activated?
When Rhodopsin binds to trans-retiNAL it moves to activate Phosphodiesterase
101
What hydrolyses cyclic-GmP?
Phosphodiesterase
102
What is cyclic-GmP hydrolysed into?
GTP
103
What causes potassium levels to increase during phototransduction?
The closing of sodium-potassium channels as the cyclic-GmP that's keeping them open is hydrolysed into GTP
104
What causes glutamate processes to lessen meaning less signals are sent to the brain?
When potassium levels go up in rods by the closing of sodium-potassium channels
105
In Rods outer membrane of disks how do the sodium-potassium channels work?
Pump in Na+ & Ca2+ Pump out K+

Anatomy & Physiology 2 (12 decks)

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