retina revision (layers of the retina)

Retinal pigment epithelium

outermost layer of retina

lies between outer segments of photoreceptors and brutes membrane of choroid

RPE functions

absorption of scattered light by melanin granules

physical support of photoreceptors outer segments

transport of nutrients from choriocapillaris

breakdown of photoreceptor discs and recycling vitamin A

Photoreceptor layer

= sight of light absorption

remember its not the only layer with photoreceptors as they extend through 4 layers

outer and inner segments in photoreceptor layer

external limiting membrane - thin layer

nucleus lies in outer nuclear layer 

axons and terminal endings in the outer plexiform layer

external limiting membrane

region of attachment between photoreceptors and muller cells

selective barrier for nutrients ( tight adherens junctions)

stabilise uppor portion of photoreceptors

muller cells

they are a type of glial cell

provides insulation between rods and cones

extend all the way through retina for structural support

largest cells in retina

outer nuclear layer

rod and cone nuclei in this layer

location of rod ad cone nuclei differ

rod- several rows about external limiting membrane

but cone nuclei close to ELM

thickest at the fovea

outer plexiform layer

contains axons and terminal endings of photoreceptors

contains dendrites of bipolar cells

terminals referred to as outer synaptic layer

axial portion referred to as Henles fibre layer

• where communication occurs between photoreceptors and bipolar cells and modified by horizontal cells

Inner nuclear layer

information passed on from photoreceptors in outer plexiform layer

contains cell bodies of horizontal, bipolar, amacrine and interplexiform neurons- they communicate with eachother

muller cells for structural insulation

inner plexiform layer

laminated

On responses(signals about increases in light intensity) go to the inner part of the layer- bipolar cells terminating closer to ganglion cells

OFF responses ( signals about decrease in light intensity) go to outer part of inner plexiform layer- synapse is closer to bipolar cells

dendrites of ganglion cells receive input from bipolar and amacrine cells

ganglion cell layer

contains cell bodies of retinal ganglion cells and some amacrine cells

ganglion cell axons make up optic nerve but is located in next layer

dendrite of ganglion cells are in inner plexiform layer(receive input from Bipolar and amacrine cell)

nerve fibre layer

made up of axons of ganglion cells(nerve fibres)

nerve fibres run perpendicular to photoreceptors

thickest at nasal edge of disc

no more editing information by retina by this point

only transmission of information to brain for processing

inner limiting membrane

innermost layer of retina

outermost layer of vitreous(hyaloid membrane)

composed of : 

collagen fibrils

HCL

basement membrane of muller cells

plasma membrane of muller cells

layers f the retina

what happens to layers at the fovea

all layers above photoreceptor layer are moved to the Sid or thinner to all all light to meet cones in photoreceptor layer

causes a dip shape

how are the photoreceptors arranged at the fovea

arranged in a cone mosaic

photoreceptors arrangment

cones are much larger than rods

at fovea - only cones in mosaic

moving further out rods and. cornea are equal in number

even further out- rods outnumber cones about 4:1

into the further periphery - rods become larger and reduce in number

blood vessels in retina

fewer further out into periphery then transitions to ora serrata