Flashcards in Absolute Threshold of Vision (M1) Deck (16)
How many photons does it take to activate one rhodopsin molecule? 1. How many transducins are activated by a active rhodopsin? 2. How many PDE are activated by a transducin? 3. How many cGMP can be hydrolyzed per second by an active PDE? 4. Therefore, how many cGMP can be hydrolyzed by a single photon? 5
What percentage of photons get back to the retina? 1. What percentage pass through the retina or are absorbed by cones? 2. What percentage of photons of the original light flash are absorbed by cones? 3
What happens as a result of spontaneous isomerization of 11-cis retinal to all-trans retinal? 1. What causes an increase in this? 2
2. higher temperatures
How often does spontaneous photoisomerization occur for a given molecule?
every 500 to 1000 years
What are the reasons rods are more sensitive than cones?
1. Stiles-Crawford effect reduces sensitivity to off-axis rays
2. cones are noisier
3. less signal amplification in cones
4. voltage response to 1 photon in cone only 1/10 or rod
5. rods more spatial and temporal summation
What is the adding together of responses that occur in different photoreceptors called?
Do rods or cones sum up more information over space? 1. What is the reason for this difference? 2
2. organization of synaptic connections between rods, bipolar cells, and ganglion cells
What is the law that states up to the critical spot diameter, threshold is independent of spot size if quanta in spot remains constant?
What is the adding together of events that occur at slightly different times?
Do rods or cones sum up more info over time? 1. What is the reason for this difference? 2
2. cones inactivate faster after photon absorption
What is the temporal summation period for the scotopic system?
What is the law that states up to the critical time duration, as long as the threshold number of quanta are delivered during this period, it does not matter how they are delivered?
How many rods in close spatial proximity must be stimulated within a short time period for perception to occur?
What does each number in the 100:10:1 rule stand for?
100: photons on the cornea
10: photons absorbed at retina
1: photon needed to get detectable response of rod
What is the absolute threshold of number of photons in a small, brief flash for a response in scotopic conditions? 1. Photopic conditions? 2