Retina Flashcards
what is the main function of the retina
where light energy is transformed into a neural signal and sent to the visual pathway
what is phototransduction
process of transforming light energy into a neural signal
what are the first 3 cells of the visual pathway
photoreceptors, bipolar cells, and ganglion cells
which interneurons modify the signal as it passes through the retina
amacrine cells, horizontal cells, and interplexiform cells
what do the neuroglial Muller Cells do
they maintain the physiologic environment of the retina
what are microglia
neuroglial cells that are wandering phagocytic cells
what are astrocytes
star-shaped cells that are in the nerve fiber layer/ganglion layer to support blood vessels and fibers
what are the innermost 9 layers of the retina called
the Sensory or Neural Retina
what is the 10th layer of the retina
the retinal pigmented epithelium (RPE)
what is the function of the RPE
to phagoctize the shed photoreceptor discs
what type of cells are in the RPE
a monolayer of cuboidal cells
what extends from the RPE to the photoreceptor layer (PR)
microvilli processes
which layer is the outermost neural layer
the photoreceptor layer (PR)
what does the PR layer contain
photopigment, rods and cones
what are the PR cells highly specialized to do
convert light energy into neural messages
which part of the PR layer is for capturing light
the outermost part
which part of the PR layer is for transmitting the neural signal
the innermost part
what parts are common between rods and cones
outer segment, cilium, inner segment, outer fiber, cell body, inner fiber, and synaptic terminal
what is the outer segment (OS)
a stack of membranous discs that are enclosed by the plasmalemma of the cell
where is photopigment located
inside the outer segment discs of the photoreceptors
where does the apex of the outer segment face
the RPE
where do the mircovilli from the RPE extend to in the PR layer
the distal third of the outer segment (OS)
what is the cilium
a connecting stalk between the OS and inner segment
what is the inner segment
two regions: ellipsoid and myoid region
what is in the ellipsoid region of the IS
mitochondria, power house
what does the myoid region of the IS contain
endoplasmic reticulum and golgi apparatus for synthesizing proteins
what is the outer fiber
extends from the inner segment to the cell body
what is inside the cell body
the nucleus of the photoreceptor
what is the inner fiber
the axon of the photoreceptor (forms the synaptic vesicles)
how many rods are there
92-120 million
what is another name for dim light
scotopic vision
what photopigment do rods contain
rhodopsin
where does the density of rods peak
in a ring about 4.5mm from the fovea
are there rods in the fovea
no only cones
how many discs are there in the rod outer segment
600-1000 discs
where is the photoreceptor rhodopsin located in the rod
in the disc membrane
when are the rod discs shed/phagocytized
early in the mornings
what is the specialized terminal of the rod inner fiber called
a spherule
what does the rod spherule contain
synapses with bipolar dendrites and horizontal processes
how many cones are there for bright vision and color
5 million
what is another term for bright vision
photopic vision
how many different opsins (photopigments) are there for regions of the light spectrum
3
what are S-cones
blue cones (420nm)
what are M-cones
green cones (531nm)
what are L-cones
red cones (588nm)
how is the cone discs shape different from the rod discs
they are wider at the base and taper toward the apex
when are the cone discs shed
in the evening
what is different about the cone nuclei from the rod nuclei
the cone nuclei are larger
what is the terminal structure of the cone called
pedicle
what is the external limiting membrane (ELM)
a dark line (dots) of zonule adherens which hold the photoreceptors to each other and to Mullers cells
what do the zonule adherens act as in the ELM
a barrier to large molecules into and out of the retina
what is the outer nuclear layer (ONL)
contains the nuclei of the photoreceptor cells
what is the outer plexiform layer (OPL)
where the synaptic terminals of the photoreceptors will synapse with the dendrites of the bipolar and horizontal cells
what does the outer plexiform layer a demarcation of
the inner retinal layers that are supplied by the central retinal artery and the outer layers supplied by the choroid
why is the outer plexiform layer a discontinuous membrane
there are many desmosome-like attachments (synaptic densities) between the processes
what is the inner nuclear layer (INL)
where cell bodies of bipolar cells, horizontal cells, amacrine cells, interplexiform cells and Muller cells are located
what does the internal nuclear layer mark/separate
the deepest part of the retina that is supplied by the central retinal vasculature
what is the inner plexiform layer (IPL)
the dendrites of the ganglion cells and the axons of the bipolar cells
what is the ganglion cell layer (GCL)
usually one cell layer thick (thicker in the macula)
where do the ganglion cells communicate with
with the central visual system structures
what is the nerve fiber layer (NFL)
unmyelinated nerve fibers (axons of ganglion cells) also the central retinal vessels
what is the internal limiting membrane (ILM)
closest to the vitreous, formed by the footplates of the Muller cells, covered by basement membranes
anteriorly, the internal limiting membrane is continuous with what other internal limiting membrane
in the ciliary body
posteriorly, at the optic disc, what are the footplates replaced with
processes from astrocytes that form the internal limiting membrane of the disc
what 3 things does the central retina contain
macula, fovea, and foveola
how big is the diameter of the macula
5.5mm
how far from the edge of the optic disc is the macula
3.5mm and 1mm below
why is the macula darker in color
the PRE cells are taller and contain more pigment
why does the macula have a yellow hue
it has increased amount of lutein and zexanthin in the ganglion and bipolar cells
what is the fovea centralis (fovea)
the part of the retina that provides the best visual acuity (only cones are found here)
how wide is the fovea
1.5mm diameter
what is the sloping down of the walls of the fovea called
clivus
is the fovea avascular
yes
which retinal layers are present in the fovea
only the outer layers (no inner)
which cells are found in the fovea
only photoreceptors (cones)
what direction are the inner fibers of the photoreceptors in the outer plexiform of the fovea oriented
horizontal (vertical in the rest of the retina)
what is the Nerve Fiber Layer of Henle
the layer in the fovea region where the photoreceptor fibers are horizontal
how wide is the foveola
0.35mm in diameter
what retinal layers are not present in the foveola
the inner, but it still has an internal limiting membrane and muller cells
what is often seen in the center of the foveola
a reflex (umbo)
what is present in the extereme peripheral retina
the rods are replaced by malformed cones near the ora serrata
what blood supplies the inner retina
the central retinal vasculature
what blood supplies the outer retina
the choriocapillaries
what does the central retinal artery split into
a superior and inferior retinal artery and then nasal and temporal branches to feed their quadrants
what are the two capillary beds in the retina
superficial and deep capillary plexus
where is the superficial capillary plexus
in the nerve fiber layer
where is the deep ciliary plexus
in the internal neuron layer
are the capillaries fenestrated in the retina
no, they are in the blood-retinal barrier
what is the ciliretinal artery
15-20% of population has it, derived from the short posterior ciliary arteries
is the blood supply of the retina neuroregulated or autoregulated
autoregulated
what veins drain the retina
central retinal vein
