Hirsch - Eye Flashcards
Surface features of the eye
Sclera - Iris - Pupil
Eyeball
Cornea & Sclera Aqueous humor in anterior chamber Ciliary muscle & choroid Retina Iris & Pupil Ciliary muscle & Zonule fibers & Lens Vitreous humor (jelly-like) Fovea Optic disk
Choroid
nourish neural part of eyeball; rods and cons
Focal planes with respect to the retina
Emmetropia
Myopia - nearsighted
Hyperopia - far sighted
ciliary muscle contract, springs (zonule fibers) …. the lens ….
when ciliary muscle contract,
zonule fibers become loose
lens focuses close object to retina
ciliary muscle relax, spring (zonule fibers) …. the lens ….
when ciliary muscle relax,
zonule fibers become tight,
lens focuses distant object to retina
myopia or nearsighted when…
eye too long
lens too round
need concave lens
hyperopia or far-sighted
eye too short
lens too flat
need convex lens
Why are rods and cons far back near choroid?
high metabolic demands
choroid nourishes the cells
Basic Retinal Anatomy from proximal to distal
light come in
—- inner limiting membrane
—- nerve fiber layer
ganglion cell layer(ganglion cells)
inner plexiform layer(amacrine cells)
inner nuclear layer (bipolar cells)
outer plaxiform later(horizontal cells)
outer nulear layer (muller cells)
—- outer limiting membrane
photoreceptor layer (rods, cones, pigment epithelium)
thickness of retina
thick centrally and thin peripherally
the fovea
visual acuity maximized cones only - smaller dense * outer cones largerand less dense * outer rods max around fovea and decrease (due to thinner retina) foveal pit (around: foveal slope)
Disease in retina
macular (foveal pit, foveal slope, para & peri fovea) degenration
retinitus pigmentosa
diabetic retinopathy
disks in conse ve. rods
cone; outer surface of disks embedded in the cell membrane; faster
rods; disks are stacked inside of cell membrane; slower
rod vs. cone
slow vs fast
less light vs more light
recording of rod during stimulation of punctate sites with a llaser
no matter where a photon lands, the whole outer segment of rod hyperpolarizes
origin of receptor currents
when dark; depolarized; sodium influx
when light; hyperpolarized; sodium block
phototransduction cascade under dark and under light
lots of cGMP in cytoplasm keep open Na channels in outer membrane
- opsin molecule (e.g. rhodopsion in rod, embeded in the disks) switches from 11-cis to all-trans (e.g. metarhodopsin)
- in all-trans state opsin activates GTP-binding protein - transducin(its alpha subunit binds GTP and activates a phosphodiesterase;PDE)
- phosphodiesterase (PDE) hydrolyzes cGMP to GMP
- concentration of cGMP drops. many cGMP fall away from NA channal closing the channel, hyperpolarizing the cell
one photon absorbed by one molecule of opsin activates — molecules of dransducin
800 molecules of transducin
each molecule of transducin activate —- phosphodiesterase
1 phosphodiesterase (PDE)
each molecule of phosphodiesterase hydrolizes
upto 6 molecules of cGMP
how does one photon affect sodium channes and membrane potential?
one photon leads to the closure of 200 sodium channels and drop 1mV in membrane potential
adaptation
great sensitivity of phototransduction cascade —> early saturation
adaptation extend the dynamic range of response
dependent on Ca (retinal Na Channel also permeable to Ca)
Na channel closure -> Ca decrease -> increased guanylate cyclase activity - increase more cGMP - and rhodopsin kinase activity - phosphorylated metarhodopsin binds arrestin interferes ability of metarhodopsin to activate transducin - (which are inhibited by Ca)
decrease in calcium concentration in Rod
increase guanylate cyclase => increase cGMP
increase rhodopsin kinase => phosphorylate metarhodopsin -> bind arrestin which conflicts with transducin
sensitivity of rods and cones
blue(cone) - rod - green (cone) - red (cone)
Ocular dominance
Perceive depth
