Light Detection- Signal Averaging

Question 1

Are gap junctions restricted to photoreceptors of the same class?

Answer 1

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

Question 2

Only ___ cones appear to remain electrically isolated from other receptor types

Answer 2

S

Question 3

Gap junctions increase sensitivity by

Answer 3

Signal averaging

Question 4

What does signal averaging do?

Answer 4

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.

Question 5

Dark adapted cones are about 100 times __ sensitive than dark adapted rods

Answer 5

less

Reason is unknown

Question 6

When sufficient light is present, ___ respond more quickly and also recover faster.

Answer 6

Cones respond and recover quicker than rods.

Question 7

Scotopic, mesonic, and photopic

Answer 7

Scotopic- night vision. Rods. No color vision, poor acuity.
Mesonic- Changing from photopic to scotopic.
Photopic- Light vision. Cones. Best acuity.

Question 8

The photochemical hypothesis: The eyes sensitivity to light depends upon the proportions of unbleached retinal photopigment available to absorb light at any moment.

Thoughts

Answer 8

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.

Question 9

Saturation of rod responses occurs when ___% of their rhodopsin is bleached

Answer 9

10%

Question 10

Rod saturation occurs when

Answer 10

When most of the cGMP-gated ion channels are closed. As luminance increases, the rods cannot continue to increase their response.

Question 11

Saturation graph comparing rods and cones

Answer 11

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.