Light Detection- HSP/Absolute Threshold and Phototransduction Flashcards
HS&P’s Experiment
Measured the eye’s absolute light detection threshold under optimal conditions.
Complete dark adaptation. Used red target to maintain dark adaption since neither rods or cones are very sensitive to red light. (red light is not easily absorbed under photopic or scotopic conditions).
Maxwellian View Presentation: Sets up certain optical arrangement so you can get max retinal illuminance on the eye without it being affected by the pupil size. Made it possible to compare test subjects with different pupil sizes.
Results: With 60% reliability. In ideal conditions, the human eye only needs one photon of light to be able to recognize that there’s light present.
Poisson Distribution
When trying to deliver a small number of photons in a “flash” of light, it is impossibly to get the exact number you want every time. The number of photons fluctuates. Ex: If you try to present 500 photons in a flash, each flash of light will be slightly off that of 500 goal.
X: Number of quanta
Y: Relative probability
Bell curve with peak at 500 number of quanta
Rhodopsin
Visual pigment of rods. Molecules imbedded in disc membranes.
Seven transmembrane receptor.
Made of chromophore or retinal and opsin.
Chromophore AKA retinal is derived from
Vitamin A, which is made fro ingested beta carotene. Eat carrots.
Vitamin A is synthesized in the liver
Your liver uses beta carotenes from diet to make
All trans retinOl. AKA vitamin A
All trans retinol travels through your bloodstream, to the choriocapillaris, and then into the RPE. In the RPE, it gets broken down into
II-cis retinAl. This travels through the inter photoreceptor matrix to get to the rod outer segment, where it joins opsin to make rhodopsin.
Rhodopsin gets broken back down during the visual cycle. The broken down rhodopsin _____
Separates back into the all trans retinOl and goes back to the RPE to help w the cycle all over again.
