Light Detection- Signal Averaging Flashcards
Are gap junctions restricted to photoreceptors of the same class?
NO. Rod: cone junctions are fairly common.
Gap junctions also occur between M and L cones.
Only S cones appear to remain electrically isolated from other receptor types
Only ___ cones appear to remain electrically isolated from other receptor types
S
Gap junctions increase sensitivity by
Signal averaging
What does signal averaging do?
It reduces random noise by the inverse of the square root of the number of signals averaged
Ex: 4 signals.
square root of (1/4)= 50%
so 4 random waveforms decreases their mean nose amplitude to 50%.
A rod-bipolar cell may receive input from 15 rods. Signal averaging makes it easier for rod bipolar cells to detect the signal from a lone hyper polarized rod.
Dark adapted cones are about 100 times __ sensitive than dark adapted rods
less
Reason is unknown
When sufficient light is present, ___ respond more quickly and also recover faster.
Cones respond and recover quicker than rods.
Scotopic, mesonic, and photopic
Scotopic- night vision. Rods. No color vision, poor acuity.
Mesonic- Changing from photopic to scotopic.
Photopic- Light vision. Cones. Best acuity.
The photochemical hypothesis: The eyes sensitivity to light depends upon the proportions of unbleached retinal photopigment available to absorb light at any moment.
Thoughts
If true, then light sensitivity should be halved when 50% of the retinal rhodopsin is bleached. So this is WRONG. Bleaching 50% of the retinal rhodopsin decreases light sensitivity by nearly 10^10 log units. Happens because we have thousands fewer cation channels in this situation. If you close the channels, the cell cannot change its voltage any further.
Saturation of rod responses occurs when ___% of their rhodopsin is bleached
10%
Rod saturation occurs when
When most of the cGMP-gated ion channels are closed. As luminance increases, the rods cannot continue to increase their response.
Saturation graph comparing rods and cones
Y axis is V/Vmax, which is voltage at any given time divided by the maximum voltage that the photoreceptor could reach.
X axis is quanta per flash.
Rods are activated sooner on the X axis, but level out around 10^9 quanta per flash.
Cones are activated later on the X axis, but don’t max out until closer to 10^11.