Ocular: Phototransduction Flashcards
What is photoreception?
Light detection that lead to vision and depends on photoreceptors
What is scoptopic vision?
Dim light and motion detection
What is photopic vision?
Color and detail
Rods are apart of which type of vision?
Scoptopic vision
Rods are good for..
Dim illumination, very sensitive
Cones are apart of which type of vision?
Photopic vision
Cones are for..
-specialized for color and detail
-less sensitive to motion detection
Where do the rods reach peak density?
-18% away from fovea
-4.5 mm outside the fovea
Where do cones reach their peak density?
Fovea
-blind spot
How many rods are there?
92-120 million rods
Peak absorption of rods?
500-510 nm
Many rods gather information onto ___ rod bipolar cell
One
The convergence of the rods to one bipolar cell increases…
Sensitivity
How many cones are there?
5-6 million
The cone photopigments are stored in the
Disc membrane
What are the 3 photopigments that cones could have?
S cones
M cones
L cones
S cones are sensitive to what wavelength?
420 nm
What wavelength are M cones sensitive to?
531-534 nm
What wavelengths are L cones sensitive to?
564-588 nm
Is there convergence of cones to one bipolar cell?
NOPE
What is the peak absorption spectral sensitivity of rod photoreceptors?
498-510 nm
What is the photopigments of rods?
Rhodopsin
What is the photopigment used by cones?
Conopsin
Rhodopsin = _____+ ________
Opsin + 11-cis-retinal
Iodopsins= ______ + ________
Photopsin+ 11-cis-retinal
What is phototransduction?
Is the series of biochemical events that lead from photo capture by a photoreceptor cell
Is the transformation of light into electrical and chemical signals that produces the perception of light
What do Cyclic-GMP-Gated(CNG) Cation channels do?
-Allow Na+ and K+ and Ca2+ to enter the cell
-causes the cells to be partially depolarized
What is the resting membrane potential of the rod photoreceptors in the dark?
-50mV
During the dark current in what state are the rod photoreceptors?
Partially depolarized
Describe the movement of cations during dark current.
-net flux of cations during flow out of the inner segment
-net flux of cations flow into the outer segment plasma membrane
What does the flux of cations cause during dark current?
The opening of CNG on the outersegment so they can enter
The opening of the CNG it’s important because?
It keeps the dark current and the rods partially depolarized by keeping the Na+ channels open in the dark
Are CNG channels of photoreceptors open or closed in the dark?
OPEN
Are CNG channels of photoreceptors are open or closed in light?
Closed
Is glutamate release by photoreceptors higher or lower in the dark?
higher
Is glutamate release by photoreceptors higher or lower in the light?
Lower
What happens to 11-cis-retinal when rhodopsin is photoisomerized?
It becomes all-trans retinol
The classical visual cycle involves the cycling of ________ between the rod outer segments and RPE.
11-cis-retinal
Where does the reduction of all-trans-retinol occur?
Outer segments of photoreceptors
Reisomerization of all-transretinol into 11-cis-retinal occurs in the ?
RPE
What does transducin stimulate?
cGMP-phosphodiesterase(PDE-6)
What does PDE6 do?
Converts cGMP to 5’-GMP
How does photoisomerization of rhodopsin change intracellular concentration level of cGMP?
Rhodopsin conformationally changes to metarhodopsin (MII)and stimulates transducin to produce cGMP PDE6
Na+ channels are kept open by high concentrations of cGMP and are therefore open or closed in the dark?
Open
When light hits, transducin is released and causes what? what happens to Na+ channels?
Transducin changes cGMP to 5’-GMP, so Na+ channels are forced to close
What is electronic spread?
In the dark, Na+ is flowing from OS to IS which causes continual depolarization of the membrane and release of neurotransmitters
Why does glutamate release form photoreceptors decrease when stimulated by light/
When the photoreceptors hyperpolarizes in response to light, it stops releasing glutamate
