Ocular Physiology Flashcards
Order this in the correct sequence:
- All-trans retinol is transported to the RPE cells
- Light is absorbed by the photoreceptor
- All-trans retinal is reduced to all-trans retinol
- 11-cis retinal is converted to all-trans retinal
- 11-cis retinal is shuttled back to the photoreceptors to be incorporated into the photopigments in the disc outer segment
- All-trans retinal moves from the disc lumen into the cytoplasm
- All- trans retinol is converted to 11-cis retinol in the RPE
2 –> 4 –> 6 –> 3 –> 1 –> 7 –> 5
Photoreceptors have approx what electrical charge in the dark?
-50 mV
The Na/K ATPase pump pumps Na (in/out) while moving K (in/out) in the inner segment?
Na OUT
K in
NOTE: Na reenters inner segment iva Na+ channels located in the OUTER segment
When PR are depolarized what NT do they release and onto what cell (“ON” cells)?
They release GLUTAMATE onto BIPOLAR CELLS
Which enzyme keeps Na+ channels open to promote depolarization with regard to the retina and PR?
cGMP
keeps Na+ channels open to promote depolarization
What is unique about PR, horizontal cells and OFF-center cone bipolar cells?
they HYPERPOLARIZE to LIGHT
What is the key event during phototransduction?
CLOSURE of Na+ channels & effectively “shutting off” the PR by DEC their release of glutamate
Dissociation of which protein triggers the activation of G proteins, TRANSDUCIN, which leads to a cascade that unltimatel results in a DEC in [cGMP] when light is absorbed?
Rhodopsin
This triggers phototransduction
What does DEC in cGMP result in?
Closure of Na+ channels thus INCREASING negative charge in the cell to -65 mV –> AKA hyperpolarization –> DEC glutamate to bipolar cells
Which retinal NT is excitatory and released by ALL rods, cones, bipolar cells & MOST ganglion cells?
Glutamate
Which retinal NT is inhibitory and released by horizontal and amacrine cells?
GABA & glycine
What happen to ON-center bipolar cells in the light?
They depolarize due to less glutamate being released which results in depolarization
RECALL that this type of bipolar cell is inhibited by glutamate
What happens to OFF-center bipolar cells in the light?
They hyperpolarize due to a DEC in glutamate which results in hyperpolarization
RECALL that this type of bipolar cell is EXCITED by glutamate
Which bipolar cell always depolarizes in response to light?
ROD bipolar cells
True or False. Horizontal cells do not have a center surround receptive field.
True
Horizontal cells hyperpolarize or depolarize in the presence of light?
Hyperpolarize
NOTE: they also respond w graded potentials the same way off-center bipolar cells and PR do in light.
True or False. Amacrine cells have center/surround receptive fields & respond with graded potentials.
FALSE.
They do have a center/surround receptive field; however, respond w ACTION POTENTIALS
Amacrine cells always depolarize or hyperpolarize in response to light?
DEPOLARIZE
NOTE; amacrine cells fine-tune the signal btwn bipolar and ganglion cells
ON-center/OFF-surround ganglion cells do what in the presence of light (de or hyper polarize?)
DEPOLARIZE
ON-center = depolarize in light (less glutamate which inhibits)
NOTE: ON-center/OFF-surround also synapse w ON-center bipolar cells
OFF-center/ON-surround ganglion cells do what in light?
HYPERPOLARIZE
NOTE: OFF-center/ON-surround synapse w OFF-center bipolar cells
Outer plexiform layer has axons of which 3 cells?
- Bipolar
- Photoreceptors
- Horizontal
“BPH”
All from the INL
Inner plexiform layer has axons from which 3 cells?
- Bipolar
- Amacrine
- Ganglion
in the “BAG”
What causes the foveal reflex to dim with age?
Thickening of the ILM
Rod density decreases with age. Does that mean the scotopic function declines as well?
NO
