Flashcards in Exam 2 Koh- Retina Biochem 3 Deck (52):
Tonic cells for _____, phasic cells for _______
What percentage of intrinsically photosensitive retinal ganglion cells are retinal ganglion cells?
What are melanopsin ganglion cells for?
Unconscious visual reflexes: pupillary constriction, daily behavioral and physiological rhythms (circadian rhythms)
How do ipRGCs respond to light?
Via the photopigement melanopsin
Melanopsin shares more homology with what?
Invertebrate rhadomeric opsins
Major excitatory transmitter of horizontal cells, ganglion cells
Functions particularly in the horizontal and amacrine cells as an inhibitory mediator
Inhibitory neurotransmitter in amacrine cells
Major excitatory transmitter of amacrine cells
Dopamine occurs in ____ cells
An amino acid closely related to Gaba and glycine, (ox bile), has unclear function, but cone degeneration is seen in cat without taurine in diet
Photoreception ranges cover ___ orders of magnitude in intensity
At any given level of adaptation we can only discriminate within an intensity range of _____ orders of magnitude
What is light adaptation?
The process by which a photoreceptor exposed to a constant background light bright enough to saturate the receptor, regains the ability to respond incrementally to brighter light stimuli
Bleaching of cone photopigment has a ______ effect on cone thresholds
Bleaching rhodopsin by 1% raises threshold by how much?
10 (decreases sensitivity by 10)
High levels of illumination bleach away photopigments making the outer segment ____ sensitive to light
Biochemical and neural feedback do what to the cone response?
The life span of activated cone opsin, its turn off, and the turn off of cone transducin are _____ than they are in rods
How big is the pupillary aperture?
1.5mm to 8mm
A ____ fold change of quantity of light entering the eye response in seconds
What are the chemical processes in the photoreceptors for bright light?
What are the chemical processes in the photoreceptors for dim light?
What is the adaptation at the neural level of light?
Retinal neurons in all layers increase or decrease signal output
In the photoreceptor outer segment, free intracellular Ca2+ can fall from ___ nM in dark-adapted rods to ____ nM on illumination
Low calcium leads to what things?
1) activation of rhodopsin kinase phosphorylates of Rh+ 2) activation of guanylate cyclase activating proteins 3) increase in affinity of cation channel proteins for cGMP
_____ adaption takes longer to achieve than ____ adaption
What happens in dark adaptation?
Rhodopsin are bleached and desensitized, cones are not stimulated, low intensity, takes about 20 min
What happens in bright adaptation?
Cones are bleached at first, then adapt to a higher threshold, about 5 min, meta II of cone pigments forms faster than that of rhodopsin, meta II decays ~10-50x faster than that of rhodopsins, clearance of Ca2+ from cone outer segments is several times faster than rods
Why do pilots wear red goggles in strong light?
Rods are insensitive to red but sensitive to other colors, if you wear a red filter then you help protect many of the rods from bleaching. If you go to a dim environment, you can take off the red filter and the rods will be ready to adapt to the dark environment
What are Muller cells?
Rid waste, phagocytosis, neuroprotection, GABA, DA, taurine, glycogen, retinoic acid synthesis, ion homeostasis
What are astrocytes?
Supportive role to the retinal ganglion cells, supports NFL, myelinating nerve fiber, covers BVs that feed the NFL, can store glycogen, ion homeostasis
What are microglias?
Can be stimulated into macrophagic function after trauma to retina
Blood flows to the ______ is relatively high in relation to other tissues
The retina has a ____ metabolic rate; glucose is _____ transported
Millions of ATP molecules is used per second by rods to run ________ actively
Na/K ATPase actively
______ is an insulin-independent tissue
How does glucose enter the retina?
From choroid and retinal blood vessels
Where are glucose transporters found?
RPE, retina, retinal blood vessels
Where is glucose stored?
As glycogen in Muller cells and also in some retinal neurons
What supplies the main source of ATP?
_____% of glucose is used in photoreceptors
Glucose is mainly used for _____ rather than fat or protein degradation
Aerobic yield is 36 ATP per glucose and is confined to the _____ segment
The isolated retina can produce ____% of its normal ATP production by glycolysis in the absence of oxygen
In hypoglycemic conditions (1 mM glucose) it generates ___% of its normal ATP needs by oxidative metabolism
Retina metbolizes majority of glucose ______ brain does it ______
The retina can also use what 3 things for ATP?
Glutamate, malate, and succinate
Retinal lipids are made up of mainly what?
What are the 2 predominant retinal lipids?
Phosphatidylcholine and phosphotidylethanolamine
High content of polyunsaturated fatty acids in the outer segment are susceptible to ______ damage