Retina

in the retina, ______ energy is transformed to _________ energy

light energy is transformed to chemical energy

the retina extends from _________ to ____________

from optic disc to ora serrata

what embryological layer does the retina come from

neural ectoderm

layers of the retina (outer to inner)

retina has 10 layers (RPE OO II GNI)

RPE, PR, ELM, ONL, OPL, INL, IPL, GCL, NFL, ILM

RPE histology

single layer of cuboidal pigmented cells

apical side of cells face the retina

basal side of cells are adjacent to bruch’s

BM adheres strongly to the choroid and forms the innermost part of Bruch’s membrane

what embryological structure is the RPE derived from

outer layer of optic cup

what is the role of the RPE

adheres to Bruch’s

takes waste out of retina: phagocytosis of outer PR segments

association of RPE with photoreceptors

the RPE does not have tight junctions with PRs

the apical side of the RPE has microvilli that extend to the PR layer and surround the PR outer segments, phagocytizing the PR outer segments and transporting them to the choriocapillaris as waste

the space between _________ and ____________ can lead to RDs

between the RPE and the neural retina

RPE adheres strongly to Bruch’s but neural retina can separate from RPE

6 functions of RPE

1. phagocytosis of PR outer segments

2. transfer of ions, water, and metabolites (nutrients & waste)

3. vitamin A storage and metabolism

4. blood-retinal barrier

5. absorbs light

6. produces growth factors (VEGF) for tissue maintenance

what organelle in RPE cells allows phagocytosis of photoreceptor outer segments

lysosomes

what happens when PR outer segments aren’t being digested by RPE cells

undigested PR material accumulates in the RPE cells and becomes lipofuscin

this can contribute to RPE cell death

what is lipofuscin

undigested PR outer segments in RPE cells

2 substances that are transported through the RPE

lactate & glucose

how is lactate transported through the RPE

proton-lactate-water co-transporter moves lactate from the RPE to the choroid

lactate is a byproduct of anaerobic respiration

how is glucose transported through the RPE

glucose transporter moves glucose from the choroid to the RPE to supply the photoreceptors

what does the RPE store and metabolize

vitamin A and retinoids

recycles it between RPE and PRs

terminal complex

links together RPE cells to maintain the blood retinal barrier

includes zonulae occludens, zonulae adherens, and maculae adherens

function of RPE pigment granules

absorb light that was not absorbed by rods and cones

what do RPE cells produce

VEGF (vascular endothelial growth factor) and PEDF (pigment epithelial derived factor)

function of VEGF and PEDF in RPE

VEGF maintains choriocapillaris function

PEDF is an antiangiogenic that balances the effects of VEGF

photoreceptor

special sensory cells with photopigments that absorb photons of light

contain inner and outer segment

are there more rods or cones

rods (120 million)

only 6-8 million cones

function of photoreceptor inner segment

produces photopigments that are transported through the cilium to the outer segment where they are incorporated into discs

parts of photoreceptor inner segment

myoid, ellipsoid, cilium

myoid

inner layer of inner segment of PR

contains ER and golgi apparatus for protein synthesis

ellipsoid

outer layer of inner segment of PR

packed with mitochondria

cilium

connects outer and inner segments of PRs

myoid vs. ellipsoid

myoid: makes, inner portion of IS, makes proteins

ellipsoid: energy, outer portion of IS, filled with mitochondria

function of photoreceptor outer segment

has stacks of membranous discs that hold photopigments produced by the inner segment

think O looks like a disc

function of PR outer segment

produces discs that surround photopigment molecules

do rods or cones have more discs

cones (1000-1200 per cone)

rods have 600-1000 discs

discs in rods vs. cones

cones: continuous, discs are continuous with plasma membrane

rods: discs are free floating, not continuous with membrane

path of disc photopigments through the photoreceptors

formed in inner segment

assembled into discs at the base of the outer segment

shed by the tip of the outer segment

phagocytosis by the RPE

function of rods

scotopic vision

detect objects under low illumination

function of cones

photopic vision, color vision

rod photopigment and wavelength it absorbs photons

rhodopsin

507 nm

rhodopsin (does/does not) detect color

does not

iodopsins

the 3 cone photopigments

each contain the same chromophore (11-cis retinal)

each differ in their protein (opsin) component

what is the chromophore in all 3 cone photopigments

11-cis retinal

name of the 3 cone photopigments and which wavelength they absorb photons

1. cyanolabe (blue): 426 nm

2. chlorolabe (green): 530 nm

3. erythrolabe (red): 557 nm

what is difference between the 3 cone photopigments

their protein (opsin) composition

where is rod density greatest

5 mm or 20 degrees from the fovea concentrically

rod ring

area where rod density is the greatest

5 mm or 20 degrees from the fovea

where are cone photoreceptors most concentrated

fovea

contains only cones

where rods terminate vs. where cones terminate

rods: spherules

cones: pedicules

location of fovea in relation to ON

5 mm temporal and 0.4 mm inferior to the center of the ON

the ELM (is/is not) a true membrane

is not

the ELM (has/does not have) cells

does not have

the ELM is formed by attachments between what

Muller cells and inner segments of photoreceptors

function of the ELM

provides structure to the retina and acts as a barrier against large metabolites

what does the outer nuclear layer consist of

cell bodies of rods and cones

what happens in the OPL

synapses between rod spherules/cone pedicles and dendrites of horizontal and bipolar cells

what are spherules and pedicles

synaptic terminals of rods and cones

synaptic terminal of cone

pedicle

synaptic terminal of rod

spherule

what cells do rods and cones synapse with in the OPL

bipolar and horizontal cells

how (specifically) do rods synapse

each rod spherule connects to 1-4 rod bipolar cell dendrites

rod spherules can also connect to horizontal cell dendrites

rod bipolar cells only connect with rod PRs

how (specifically) do cones synapse

each cone pedicle has a synaptic triad of either:

• 3 horizontal cell dendrites

• 2 horizontal cell dendrites and 1 bipolar cell dendrite in the middle in an invagination in the cone pedicle

cone pedicles can synapse with midget, flat, or diffuse flat bipolar cells

are rod spherules or cone pedicles larger

cone pedicles

where is the site of the first synapse of the visual pathway

OPL

what is Henle’s fiber layer

the OPL in the macula

where does the OPL receive its blood supply

only retinal layer to receive dual blood supply from the choroid and the retina (CRA)

retinoschisis

splitting of the OPL

where are hard exudates located

OPL

what cells can be found in the INL

amacrine, bipolar, horizontal, interplexiform, Muller

role of bipolar cells

carry signals from PRs to RGCs

where and what do bipolar cells synapse with

OPL: PRs

IPL: RGCs

4 types of bipolar cells

rod, midget, flat, diffuse flat

midget bipolar cells

have a 1:1 connection with cones and a 1:1 connection with RGCs

resolve very fine details (20/20 vision)

found in the fovea

which cells are responsible for fine vision and found in the fovea

midget bipolar cells

flat bipolar cells

connect with several cone PRs

do flat or diffuse flat bipolar cells connect with more PRs

diffuse flat

where do horizontal cells synapse and with what

synapse in the OPL

lateral signals between PRs, bipolar cells, and other horizontal cells

modification of information that reaches the bipolar cells by horizontal cells

lateral inhibition

horizontal cells provide ________ to PRs

inhibitory feedback

horizontal cells provide ____________ to bipolar cells

inhibitory feed forward

interplexiform cells

carry information vertically between the IPL and the OPL

role of amacrine cells and what cells they synapse with

amacrine cells carry information laterally in the IPL

connect bipolar, interplexiform, amacrine, and RGCs

most common glial cells in the retina

muller cells

role of muller cells and where they stretch through

stretch from the ILM to the ELM

provide structural and nutritional support in the retina

what 2 cells in the retina provide inhibitory feedback

amacrine and horizontal cells

both carry info laterally

1st, 2nd, and 3rd order neurons of the retina

1st: PRs

2nd: bipolar cells

3rd: RGCs

what happens in the IPL

bipolar cells synapse with RGCs

amacrine cells modify the synapse via temporal input

what do bipolar cells synapse with in the IPL

one process from an amacrine cell

one dendrite from a ganglion cell

bipolar cells ______ the stimulation of RGCs

amacrine cells ______ the stimulation of RGCs

bipolar cells increase

amacrine cells decrease

the 2 cells have opposite effects on RGCs

what is in the GCL

location of ganglion cell bodies

path of RGC axons

each RGC has a singular axon that travels within the ON and ends in the LGN or other areas of the brain

where are there no RGCs

foveola

there are ____ RGC layers in the outer macular region

there are ____ RGC layers in the rest of the retina

4-7 in outer macula

1-2 in rest of retina

2 main categories of RGCs

P-cells (parvocellular)

M-cells (magnocellular)

are P-cells or M-cells larger

M-cells

have larger diameter axons

are P-cells or M-cells more common

P-cells

role of P-cells

sensitive to color and fine detail

role of M-cells

sensitive to dim changes in illumination and motion

where do P-cells project to

parvocellular layers of LGN: 3, 4, 5, 6

where do M-cells project to

magnocellular layers of LGN: 1, 2

2 types of P-cells

P1 cells: midget ganglion cells

P2 cells

are P1 or P2 cells larger

P2

what is the most common RGC

P1 cells/midget ganglion cell