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biochemistry of visi
biochemistry of vision
| Question | Answer |
|---|---|
| what are the seven layers of the retina | RPE, photoreceptor, external limiting membrane, outer nuclear layer, outer plexiform layer, inner nuclear layer, inner plexiform layer, ganglion layer, nerve fiber layer, internal limiting membrane |
| what are the structures of photoreceptor cells | outer segment, connecting stalk, inner segment, outer fiber, cell body, inner fiber |
| what does the outer segment of photoreceptor cell contain? | visual pigment molecules for the conversion of light into a neural signal |
| what does the connecting stalk of photoreceptor cells contain? | the cilium |
| what does the inner segment of the photoreceptor cell contain | metabolic apparatus |
| what does the outer fiber of the photoreceptor cell contain? | it extends from the inner segment to the cell body |
| what does the cell body of the photoreceptor cell contain? | the nucleus |
| what does the inner fiber of the photoreceptor cell contain? | ends in a synaptic terminal |
| what does the membranous discs of the outer segment of the cone contain? | vitamin A, which binds light |
| these cells allow us to take in light and adjust that into a neural signal, turning it into a neurotransmitter | rods and cones |
| how do bipolar cells communicate with each other? | via neurotransmitters |
| what are the three classes of neurotransmitters? | small molecule, nuropeptides, gases (ex: NO) |
| to be classified into a NT, a molecule must have these three characteristics: | bust be stored, released, and degraded |
| what are two classifications of NT receptors? | ionotropic (ion channel), metabotropic (G protein coupled receptors) |
| Dopamine pathway is destructive in what disease? | parkinsons |
| dopamine is made form this amino acid | tyrosine |
| these molecules degrade the NT dopamine after it does its job | MAO and COMT |
| dopamine binds to this after binding to the post-synaptic membrane, causing phosphorylation of the ion channel, resulting in depolarization | adenylate cyclase |
| what is the NT of choice in the retinal neurons? | glutamate |
| how is glutamate formed? | it is formed from glutamine via the enzyme glutaminase |
| which type of cells recycle glutamate afterwards? | glial cells |
| this is a major inhibitory neurotransmitter, and is synthesized from serine | glycine |
| where do glutamate and glycine come from? | glutamate comes from TCA cycle, glycine comes from glycolysis |
| do cells of the retina operate mostly under aerobic or anaerobic processes, and what do they produce a lot of as a result? | anaerobic, producing a lot of lactate |
| the retina is located where? | between the vitreous and coroid |
| how does the retina allow us to see? | it takes light (photons) and converts it into a neurological signal to our brain that allows us to see |
| it the retina, there are no attachments, so how does it stay attached? | via intraocular pressure, osmotic pressure, fluid transport across the RPE, and presence of vitreous in microvilli |
| what are the two types of photoreceptor cells? | rods and cones |
| how is NO made? | glutamate is released and binds to its ionotropic receptor and makes NO, which goes in a retrograde fashion, activating pre-synaptic as well as other neurons and eventually the NO is detoxified and broken down by glial cells |
| what makes NO a special neurotransmitter? | it is a gas, and acts as a retrograde NT |
| these are second order neurons in the visual pathway. they relay information from photoreceptors to horizontal,k amacrine, and ganglion cells and receive extensive synaptic feedback from amacrine cells | bipolar cells |
| what is the NT of choice for bipolar cells? | glutamate |
| these can be either bipolar (single axon and single dendrite) or multipolar (single axon with more than one dendrite) | ganglion cells |
| what is the neurotransmitter of choice for ganglion cells? | glutamate |
| these cells transfer information in a horizontal direction parallel to the retinal surface. they have 1 long axon and several short dendrites with branching terminals. horizontal cell synapse with phootoreceptors, bipolar cells, and other horizontal cells | horizontal cells |
| horizontal cells are throught to modify responses of ________ but not _______ | they are thought to modify responses of cones, but not rods |
| these cells have a large cell body, a lobulated nucleus, a single process with extensive branches and extends into the inner plexiform layer | amacrine cells |
| what are the NTs of choice for amacrine cells? | glycine and GABA |
| this layer of hte retina consists of a single layer of pigmented cells. there are four to six million of these cells and each one interacts with thirty to forty NTs | RPE layer |
| this layer of the retina contains the outer and inner segments of rods and cones, projections from the apical surface of muller cells extend into the PR layer | photoreceptor layer |
| this layer is not a true membrane but is composed of zonula adherence junctions between photoreceptor cells and between photoreceptors | external limiting membrane |
| this layer contains rods and cone cell bodies. cone cell bodies and nucleus are larger than rod cells | outer nuclear layer (ONL) |
| this layer has a wide external band composed of inner fibers of rods and cones and a narrower inner band consisting of synapses between photoreceptor cells and cell from the inner nuclear layer | outer plexiform layer (OPL) |
| this layer consists of cell bodies of horizontal cells, bipolar cells, amacrine cells, interplexiforme neurons, muller cells, and some ganglion cells. | inner nuclear layer (INL) |
| this layer consists of synaptic connections between the axons of bipolar cells and dendrites of ganglion cells. it contains the synapse between the second order and third order neuron in the visual pathway | inner plexiform layer |
| this layer is generally a single cell thick except near the macula whre it might be eight to ten cells thick and the temporal side of the optic disc where it is two cells thick | ganglion cell layer |
| this layer consists of ganglion cell axons | nerve fiber layer |
| this forms the innermost boundary of the retina | internal limiting membrane |
| in this retinal abnormality, there is damage to the RPE, causing bleeding | retinopathy |
| in this retinal abnormality, there is tissue destruction and bundles of blood | best's disease |
| this layer of retina is resp for energy metabolism. the zona occludens which joins the cells is part of hte blood-retinal barrier and is responsible for controlling nutrients and metabolism from the choriocapillaris into the retina and removing waste. | RPE layer |
| what are some funcitons of the RPE layer | ion transport, glucose transport, water transport, lactate, energy requirements, growth factor production, lysosomes within the RPE break down parts of the photoreceptor outer segments disc, Vitamin A |
| what is the primary energy source of retinal metabolism | glucose |
| the retina switches between what two types of metabolism? | glycolysis to oxitative metabolism |
| the retina has a high rate of this metabolic process | anaerobic glycolysis |
| these cells in the retina store glycogen, providing a ready source for glucose | muller cells |
| what is the consumption of energy in retina compared to other CNS neurons? | oxygen use by photo receptors is three to four times higher than other CNS neurons. |
| are photoreceptors more active in the dark or in light? | in light |
| why are photorecepotrs more active in the dark? | in the dark, the NT's are depolarzied and are making glutamate, so they are sing a lot of oxygen in the dark |
| this is considered the main chromophore in the retina | vitamin A |
| this cell in the retina senses light | chromophore |
| this cell in the retina is a membrane spanning protein | opsonin |
| what are the three main forms vitamin A exists in? | retinol, retinal, retinoic acid |
| what are some significant food sources for vitamin A | liver, dark green leafy vegetables, yellow-orange vegetables, fruit, and fortified foods. |
| what are some functions of vitamin A | vision, immune function, reproduction, cell proliferation, cell signaling |
| how is vitamin A stored in the intestinal lumen? | as retinol and beta carotene |
| how is vitamin A stored in intestinal epithelial cells? | as beta carotene, or retinyl esters |
| how is vitamin A stored in the blood | retinyl esters in chylomicrons or RBP retinol |
| how is vitamin A stored in liver parenchymal cells | retinyl esters, RBP retinol, |
| how is vitamin A stored in liver satellite cells? | retinyl esters, retinol |
| this type of reaction allows the photon to be converted into a neurochemical signal, absorbed by a chromophore. | cis retinal to trans retinal via the process of phototransduction |
| phototransduction requires what | retinal |
| what form is retinal in during the dark phase? | 11 cis retinal |
| what form is retinal in during the light phase? | 11 trans retinal, which activates a signal transduction pathway |
| which cell (rods or cones) are more sensitive to light stimulus? | rods |
| which cells are a higher abundence of photosensitive pigments | rods |
| which cell is specialized for day vision | cones |
| which cell is specialized for night vision | rods |
| which cell is more involved in acquity of vision? | cones |
| when do cone cells saturate? | when light is very intense |
| when do rods saturate? | in day light |
| which cells mediate color vision | cones |
| which cell has a higher concentration in the fovea | cones (rods are absent in the fovea) |
| which cell is more numerous | rods |
| what happens when you don't have enough vitamin A? | night blindness, ocular functions, depressed immune functions |
| what populations are mostly affected with vitamin A deficiency? | SE asia, africa, central and osuth american populations |
| what are some diseases associated with vitamin A deficiency? | night blindenss, blindness, xeropthalmia, keratomalacia, keratinzation of tracheal epithelium |
| what are some toxicities associated with vitamin A? | teratogenic effects, liver disease, dryness, erythema, scaling and peeling of skin, hair loss, nail problems |
Created by:
aferdo01
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