4 Ganglion Cell Layer Flashcards
do GC dendritic fields overlap?
yes
what cells are GCs influenced by?
bipolar cells and amacrine cells
what’s antagonistic surround good for?
- concentric organisation promotes contrast sensitivity
- relies on dendritic span of GCs
what cells have sustained responses until stimulus changes? what about GCs?
- PRs, HCs, BCs, maybe amacrine
- GCs fire APs at increased rate or fire brief high frequency bursts - intensity coded by frequency
when can a transient response be generated by GCs?
GC can only fire between bipolar cell excitation and amacrine cell inhibition
number of ganglion cell types and 3 well-known ones that stratify in LGN?
- 17 cell types
- 13 project in LGN; well known are midget, parasol, small bistratified
what are the GC inputs from midget?
- dendritic arbours like bipolar
- on and off pathways signalled by on and off midget bipolar cells
what are the GC inputs from parasol?
- dendritic arbours widespread
- on and off pathways signalled by on and off diffuse bipolar cells
what are the GC inputs from small bistratified?
- on signals by blue cone BCs
- off signals by diffuse bipolar cells
what GC types correlate to P, M and K cells?
what colour opponencies are they associated with?
- P - midget, RG
- M - parasol, broadband
- K - small bistratified, B on, Y off
which cell types go to which layers of the LGN?
- midget cells/parvocellular layers 3-6
- parasol cells/magnocellular layers 1-2
- small bistratified cells/koniocellular layers
midget vs. parasol fields across retina? what are these cells good at?
- midget fields smaller than parasol
- midget cells provide detail
parasol cells provide info about intensity variations over larger distances
what other cells are in the GCL?
- ipRGCs
- displaced amacrine
- astrocytes
- microglia
describe ipRGCs
- 5 subtypes
- contain melanopsin
- regulate light-dependent processes
- not in fovea (not involved with high acuity)
what other cells do ipRGCs connect to?
- displaced GCs that didn’t move forward during embryogenesis
- bipolar cells
compare ipRGCs to rods and cones
- ipRGCs in inner retina vs. outer retina
- cell bodies in INL/GCL vs. ONL
- melanopsin vs. rhodopsin (rods)
- synapse with bipolars/amacrine vs. others
ipRGC response characteristics
- depolarise with light
- unitary response larger than other GCs - prolonged response improves sensitivity by summing info temporally
- peak sensitivity between rods and cones
- the higher the intensity, the longer the response
sustained vs transient responses
- sustained - ipRGC only and ipRGC with rods (rods shorten response)
- transient - ipRGC wtih rods/cones (colour opponency - firing with RG on or S off)
melanopsin
7 transmembrane protein
chromophore regeneration
vertebrate ipRGC same as vertebrate cone but without RPE involvement
what markers will show up with ipRGCs?
- Brn3b is a marker for RGCs
- Opn4 is a marker for melanopsin
where do the ipRGCs project to?
- SC superior colliculus (pupillary reflex)
- SCN suprachiasmatic nucleus (entrainment) - master clock
- OPN olivary pretectal nucleus (pupillary reflex)
- IGL interfeniculate leaflet (entrainment)
- LGN (image formation)?
what are the roles of ipRGC?
- circadian photoentrainment
- pupillary light reflex
- migraine photophobia (unresolved)
- sleep/alertness homeostat (unresolved)
- mood (unresolved)
where do astrocytes come from?
where are they after development?
morphology?
function?
- not derived from retinal neuroepithelium
- in NFL - stellate at periphery, elongated at ON
- axonal and vascular glial sheaths
microglial cell origin?
precursors for what during development?
where are they found?
function?
- mesodermal
- precursors of retinal blood vessels
- all layers of retina
- macrophages and phagocytose degenerating retinal neurons
summarize rod pathway
- rod –> rod bipolar in OPL
- rod bipolar –> amacrine AII and A17 in IPL
- amacrine –> GCs
summarize cone pathway
- cone –> cone bipolar –> GCs
- more direct, narrower and more convergent than rod pathway
- low convergence, but even worse in midget system
convergence at or near fovea
- 1:1
- high density, small cones here
foveal and parafoveal circuitry
- every foveal cone has dual midget pathways - one on and one off midget bipolar
- eg. every on bipolar synpases with on GC and vice versa with off
peripheral cone circuitry
- multiple bipolars synapse with a single GC
- cone convergence increases with increasing distance from fovea
centre-surround are mediate by what?
- HC lateral inhibition
- amacrine cell contributions to retinal hypercircuit
foveal sampling units
- smallest in fovea, dominated by cone signals
- units provide high spatial resolution but insensitive to low light (no rods)
- 1:2:2 cones:BC;GC
parafoveal sampling units
- rods and blue cones significant
- unit bigger than in fovea
- spatial resolution less than fovea, but these are trichromatic and work well in low light
- 1:1 blue cone:BC
peripheral sampling units
- rods dominate
- very very large units - big dendritic fields
- convergence 10:1
- most sensitive to low light
