Term
| What is the first step in signal transduction in the retina? |
|
Definition
| photon absorption by visual pigments |
|
|
Term
| What converts the signal from analog to digital format? |
|
Definition
| retinal integrator circuits at the ganglion cell level |
|
|
Term
| What are the two layers of the retina? |
|
Definition
| outer RPE and inner neural retina |
|
|
Term
| What is the origin of the two laminar layers of the retina? |
|
Definition
| apex to apex invagination of the ectodermal layer |
|
|
Term
| How many general classes of cells are found in the retina? |
|
Definition
|
|
Term
| How thick is the photoreceptor layer? |
|
Definition
|
|
Term
| What is a horizontal cell? |
|
Definition
| connects PR to one another, between the PR and bipolar cells; mediates signal between the PR and bipolar cells. |
|
|
Term
| What is an amacrine cell? |
|
Definition
|
|
Term
|
Definition
| dendrites --> visual cortex |
|
|
Term
| Where are horizontal cells found? |
|
Definition
| outer plexiform layer of retina between PR's and bipolar cells |
|
|
Term
| What are the three main types of cone PR's? |
|
Definition
| long wavelength, middle wavelength, short wavelength |
|
|
Term
|
Definition
|
|
Term
| What is a Vit A based chromophore? |
|
Definition
|
|
Term
| What is the signal mechanism of opsins? |
|
Definition
| heterotrimeric G proteins |
|
|
Term
| What are ciliary visual pigments? |
|
Definition
| rods and cones that hyperpolarize to light |
|
|
Term
| What is the ciliary visual pigment called? |
|
Definition
|
|
Term
|
Definition
|
|
Term
| How many rhodopsins are found in each ROS? |
|
Definition
|
|
Term
| Where does rod phototransduction occur? |
|
Definition
| ciliary outer segment of the PR cell |
|
|
Term
| What causes retinitis pigmentosa? |
|
Definition
| genetic mutation for rhodopsin |
|
|
Term
| What wavelength of light is rhodopsin most sensitive to? |
|
Definition
|
|
Term
| How many transmembrane proteins are found in the AA sequence of rhodopsin? |
|
Definition
|
|
Term
| What are the terms for rod and cone rhodopsins? |
|
Definition
| rod = scotopsins; cone = photopsins |
|
|
Term
| Are rhodopsins apoproteins? |
|
Definition
| Yes, requires 11-cis-retinal prosthetic group |
|
|
Term
| What is transducin's pathway? |
|
Definition
| activates phophodiesterase --> converts cAMP into cGMP |
|
|
Term
| What actually absorbs the light in the apoprotein? |
|
Definition
| retinal integrator circuits at the ganglion cell level |
|
|
Term
|
Definition
|
|
Term
| What does light do to retinal? |
|
Definition
| Converts it from the cis conformation into all trans conformation |
|
|
Term
| Upon activation by light, what subunit of the G protein cleaves? |
|
Definition
|
|
Term
| What maintains the dark current? |
|
Definition
| cGMP gated cation channels |
|
|
Term
| What is the dark current? |
|
Definition
| steady inward current of Na+ in darkness |
|
|
Term
| is the rod cell depolarized or hyperpolarized in dark? |
|
Definition
|
|
Term
| What closes when the rod is exposed to light? |
|
Definition
|
|
Term
| What does cGMP channel closing cause? |
|
Definition
| stops Na+ flow, hyperpolarizes cell |
|
|
Term
| When is glutamate release from rod's the greatest? |
|
Definition
|
|
Term
| What does phosphodiesterase do to cGMP? |
|
Definition
|
|
Term
| What does reduced cGMP concentration cause? |
|
Definition
| closes cGMP gated channels, hyperpolarizes cell --> reduced glutamate release |
|
|
Term
| Through signal amplification, what can one photon cause? |
|
Definition
| hundreds of ion channels to close |
|
|
Term
| What is the pathway for signal amplification? |
|
Definition
| 1 photon converts rhodopsin --> R*; one R* activates 20 transducins; 20 transducins activate 20 phosphodiesterase |
|
|
Term
| What is the ratio of cGMP hydrolyzed per R*? |
|
Definition
|
|
Term
| What does guanylate cyclase do? |
|
Definition
| Converts GMP into cGMP so it can be used in the signal transduction pathway |
|
|
Term
|
Definition
| protien that regulates signal transduction in the retina |
|
|
Term
| What deactivates phosphodiesterase? |
|
Definition
| PDEy reassociates with GtBy after GTP hydrolysis |
|
|
Term
| What does the affinity for cGMP facilitate? |
|
Definition
|
|
Term
|
Definition
| cyclic-nucleotide gated channel |
|
|
Term
| Are CNG's selective to monovalent and divalent cations? |
|
Definition
|
|
Term
| What is the structure of CNG? |
|
Definition
| tetrameric complex, made of A and B subunits, each of which has a single cGMP binding site |
|
|
Term
| What provides 15% of the dark inward current? |
|
Definition
|
|
Term
| What does lowering the concentration of calcium cause? |
|
Definition
| activates guanylate cyclase (GC), reduces cGMP affinity for the channel, so channels open as Ca++ falls |
|
|
Term
| Which phototransduction mechanism is not understood as well? |
|
Definition
|
|
Term
| Is Ca++ feedback faster in rods or cones? |
|
Definition
|
|
Term
| What does RAL stand for when used as a suffix? |
|
Definition
|
|
Term
| What does ROL stand for when used as a suffix? |
|
Definition
|
|
Term
| What are the six steps of the retinoid cyce? |
|
Definition
1) all-trans-RAL transports from outer segment (OS) discs
2) reduce from aldehyde to alcohol (all-trans-ROL)
3) transfer alcohol form to RPE cell
4) esterification of ROL form in RPE cells
5) synthesis of 11-cis-ROL
6) oxidation of 11-cis-ROL to 11-cis-RAL |
|
|
Term
| What is the half life of rhodopsin in the dark? |
|
Definition
|
|
Term
| How less sensitive is a cone than a rod? |
|
Definition
|
|
Term
|
Definition
| the spontaneous noise inherent of opsin that reduces cone sensitivity, but also gives a much faster photoresponse of cones |
|
|
Term
| Why are intracellular carrier proteins necessary for chromophore shuttling? |
|
Definition
| chromophores are highly hydrophobic, needs hydrophilic carrier |
|
|
Term
| What fibers project to the hypothalamus? |
|
Definition
|
|
Term
| What is the third type of photoreceptor? |
|
Definition
| intrinsically photoreceptive retinal ganglion cells |
|
|
Term
| What nuclei are innervated by retinal ganglion cells? |
|
Definition
| SCN (circadian rhythm) olivary pretectal nucleus (pupillary light reflex), other accessory visual fxn |
|
|
Term
|
Definition
|
|
Term
| How many cones are there? |
|
Definition
|
|
Term
| What is the suprechiasmatic nucleus? (SCN) |
|
Definition
|
|
Term
| What % of fibers do NOT go to the LGN? |
|
Definition
|
|
Term
| What part of the photoreceptor interacts with the ganglion cell? |
|
Definition
|
|
Term
| What is a presynaptic ribbon? |
|
Definition
| a large area for multiple dendrites to be innervated |
|
|
Term
| What is secreted by the presynaptic ribbon? |
|
Definition
| glutamate, higher release in the dark |
|
|
Term
|
Definition
| Analogous to the axon end of a neuron, where the optical signal leaves the photoreceptor |
|
|
Term
| What kind of glutamate receptor is seen in OFF cone bipolar cells? |
|
Definition
| ionotropic glutamate receptor |
|
|
Term
| What kind of glutamate receptor is seen in ON cone bipolar cells? |
|
Definition
|
|
Term
| Where do OFF bipolar cells go? |
|
Definition
|
|
Term
| Where do ON bipolar cells go? |
|
Definition
|
|
Term
| When are ON bipolar cells activated? |
|
Definition
|
|
Term
| What other membrane is the RPE similar to? |
|
Definition
|
|
Term
| What are the fxn's of the RPE with regard to the photoreceptors? |
|
Definition
| light absorption Epithelial transport, phagocytosis, secretion, visual cycle |
|
|
Term
|
Definition
single layer of columnar epithelial cells
long apical microvillus
serves as a blood-retinal barrier |
|
|
Term
| How many RPE cells are there per eye? |
|
Definition
|
|
Term
| How many PR's per RPE cell? |
|
Definition
|
|
Term
| What % of the RPE is water weight? |
|
Definition
|
|
Term
| What substances make up the RPE? |
|
Definition
| proteins, lipids, nucleic acids |
|
|
Term
| How many proteins have been identified in RPE? |
|
Definition
|
|
Term
| What is the main carbon source for the RPE? |
|
Definition
|
|
Term
| What saturated FA's are found in the RPE? |
|
Definition
|
|
Term
| What optical quality does the RPE contribute to? |
|
Definition
|
|
Term
| Describe the blood flow to the RPE |
|
Definition
| higher perfusion than kidney |
|
|
Term
| Describe the blood flowing from the RPE |
|
Definition
| still has 90% (vs 45% elsewhere) O2 saturation, poor O2 utility in the RPE |
|
|
Term
|
Definition
|
|
Term
| What can cause OCA1 and OCA2? |
|
Definition
| tyrosinase gene defect and pink-eyed dilution gene |
|
|
Term
| What does reduced melanin do to ocular development? |
|
Definition
| impairs foveal development |
|
|
Term
|
Definition
| lack of pigment in the eye, but normal pigmentation in hair and skin |
|
|
Term
| What are the three ways RPE prevents toxin damage? |
|
Definition
Light absorption:
antioxidants
repair of DNA, lipids, proteins |
|
|
Term
| How does lipofuscin interact with the RPE? |
|
Definition
| Lipofuscin accumulates over lifespan, while initially helpful, can reach harmful levels later in life |
|
|
Term
| What color of light breaks down lipofuscin into toxin? |
|
Definition
|
|
Term
| What are the common antioxidants found in the RPE? |
|
Definition
| superoxide dismutase, catalase, carotenoids, glutathione, alpha-tocopherol (Vit E) |
|
|
Term
| What accumulates to cause AMD? |
|
Definition
|
|
Term
|
Definition
reduced RPE cell density
reduced antioxidants (alpha tocopherol) |
|
|
Term
| What organelles are modified in AMD? |
|
Definition
reduction of melanosomes
melanolysosomes (byproduct of melanin degradation) |
|
|
Term
| What causes accumulation of AGE's? |
|
Definition
|
|
Term
| What can AGE presence induce? |
|
Definition
| choroidal neovascularization |
|
|
Term
|
Definition
| increases sensitivity of RPE to blue light, combines with O2 when in the presence of blue light to create A2E-epoxides |
|
|
Term
| Where does A2E come from? |
|
Definition
| RPE does not convert all-trans-retinol into 11-cis-retinal properly |
|
|
Term
| What can inhibit cytochrome oxidase in resperiation chain? |
|
Definition
|
|
Term
| What can excess A2E in RPE inhibit? |
|
Definition
| digestion of phagocytosed PR segments |
|
|
Term
| What is the initial sign of drusen? |
|
Definition
|
|
Term
| What is the most important sign for AMD? |
|
Definition
|
|
Term
|
Definition
| between RPE and Bruch's in the basal lamina |
|
|
Term
| What are the waste products seen in drusen? |
|
Definition
| hydrophobic metabolic end products, lipoproteins, assorted PR and RPE wastes |
|
|
Term
| What is a disciform scar? |
|
Definition
| The end stage of AMD where RPE and PR's are lost over a large area, choroidal neovascularization that can leak --> wet form |
|
|
Term
| What is geographic atrophy? |
|
Definition
| loss of RPE and PR's over a large area |
|
|
Term
|
Definition
| antioxidant supplements recommended for those with an intermediate risk of developing AMD |
|
|
Term
| Why should smokers avoid beta carotene? |
|
Definition
| it increases risk of lung cancer |
|
|
Term
| What role does the RPE play in water balance in the eye? |
|
Definition
| RPE transports subretinal space metabolic H2O |
|
|
Term
| What is necessary for the RPE to adhere to the retina? |
|
Definition
|
|
Term
| What do Muller cells in the inner retina do? |
|
Definition
|
|
Term
| What is the orientation of io and water movement across the RPE? |
|
Definition
| from apical side --> basolateral (blood) side |
|
|
Term
|
Definition
|
|
Term
| How does the RPE provide glucose for the PR's? |
|
Definition
| glucose transporters in both apical and basolcateral membranes |
|
|
Term
| How does the RPE provide retinol (Vit A) to the PR's? |
|
Definition
| takes in retinol from blood stream, transports it to PR's |
|
|
Term
| What adheres the retinal to the RPE? |
|
Definition
| passive IOP, interdigitation of outer segments and RPE microvilli, active transport of subretinal fluid |
|
|
Term
| What is the rate of fluid transport across the RPE? |
|
Definition
|
|
Term
| What can cause RPE to detach? |
|
Definition
| breakdown of transport mechanisms across the RPE |
|
|
Term
| What is the interphotoreceptor matrix? |
|
Definition
| space between RPE and PR's |
|
|
Term
| What is docosahexaenoic acid? |
|
Definition
| a component necessary for neurons and PR membranes, provided by transport through the RPE |
|
|
Term
| What is the turnover for an outer segment membrane? |
|
Definition
|
|
Term
| What is found in old PR OS'? |
|
Definition
| high free radical concentration, photo-damaged proteins and lipids |
|
|
Term
| What PR molecule is recycled after an OS is shed? |
|
Definition
| retinal, docosahexanoic acid |
|
|
Term
|
Definition
| antiangiogenic factor, inhibits endothelial proliferation |
|
|
Term
| What is secreted in low levels by a healthy RPE? |
|
Definition
|
|
Term
| What does VEGF stabilize in endothelium? |
|
Definition
| permability by stabilizing fenestrations |
|
|
Term
| What does PEDF protect against? |
|
Definition
| glutamate induced or hypoxia induced neural apoptosis |
|
|
Term
| How many layers are in Bruch's membrane? |
|
Definition
|
|
