Vision

Question 1

Retinal layers

Answer 1

-Retina is 0.3 mm thick - about the thickness of tissue paper
-The black pigment epithelium behind the retina. It nourishes photoreceptors and absorbs stray light
-The photoreceptors, rods and cones are in front of pigment epithelium
-Interneurons connect the photoreceptors to the ganglion cells
-Ganglion cells are the retina’s output neurons, closest to the lens and front of the eye
-therefore, light has to travel through the whole structure of the eye, then through the retina structure and then reach the photoreceptors and stimulate the photoreceptors to become activated

Question 2

Photoreceptors come in two types: Rods and Cones

Answer 2

-outer segment: part of the photoreceptor that contains rhodopsin molecules or molecules like that that can absorb light. More extensive in rods than cones

-Why rods are very good and are designed for dim light vision to detect very low levels of light

-if you are using your rods and only your rods then everything will be a grayscale, you wont be able to see any color. You also would not be able to read whats right in front of you because rods don’t have spatial resolution

Question 3

Components of rods and cones

Answer 3

-disks are within the rods and cones. Inside the disks are the rhodospin molecules that absorb light.
-rhodospin is made of retinal and opsin. Retinal absorbs the light and opsin is a protein
-In cones there are a variety of different opsins which is important because it allows cones to either be red sensitive, green sensitive, or blue sensitive

Question 4

Phototransduction

Answer 4

-transduction mechanism in a rod is that light is absorbed by rhodopsin molecule somewhere in the disks. That rhodopsin molecule, which is a G-protein coupled receptor, and the ligand is a photon of light. So that photon of light is absorbed by the rhodopsin which changes confirmation and activates a G-protein.

-Rods and cones typically have high levels of cGMP. But when light activates rhodopsin it activates this enzyme that breaks down cGMP
-When you break down cGMP youre not longer holding the sodium channel open.
-cGMP opens the sodium channel and sodium comes in and depolarizes the photoreceptor

Summary: photoreceptors are depolarized in the dark because of the constant influx of sodium. And when light hits the photoreceptor it closes the channel and the cell hyperpolarizes. Photoreceptors are depolarized in the dark and hyperpolarizes in the light.
when they are depolarized theyre most active and sending out neurotransmitter to the rest of the retina. In light that transmitter is shut off because of the turning off of this channel.