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Eye: Black and White
Transcript of Eye: Black and White
"New Function for Rods in Daylight"
Friedrich Miescher Institute of Biomedical Research
By: Botond Roska
19 November 2014
Botond Roska and his group have identified an unique function for rod receptors cells during daylight. Rods help increase contrast information at times when they are not directly sensing light. During times of bright light, the rods meditate a so called surround inhibition. This is an important feature because it allows the retina not only to transmit information about exposed light, but also about contrast. It just shows how the brain repurposes the function of the rods when they are not directly sensing light.
Anatomy of Rod Photoreceptors
120 million rods in the human retina
slim rod-shaped structures
inner portion of rods filled with mitochondria
they are photoreceptors, so they respond to light
more sensitive than cones, but respond slower to light stimulation
activated once light reaches the retina
How Do We See Black and White?
Our eyes can detect light. The rods and cones of our eyes stimulate light and send signals to the brain.
When the cones of our eyes are at the same level of stimulation the brain perceives the color as white. Black is perceived when none of the cones are stimulated.
We see the color white and black through our rods. Rods detect light at a lower level than cones, this is why we see black and white in dimly lit rooms or at night.
Black & White Vision
Pathway to the Brain
The optic nerve leaves the eyeballs posteriorly.
The optic nerve enters the optic chiasm through the optic canal.
90% of the left nerve fibers of each eye goes to the left side of the brain, and the right nerve fibers of each eye goes to the right side of the brain.
The signals have to pass through the sensory relay nucleus, called the
lateral geniculate body
(LGB), in the thalamus before entering into the brain.
The other 10% enter the midbrain medially to reach the superior colliculus.
The LGB axons sends an electrical signal to the cell bodies of neurons, forming "optic radiation".
Axons of the optic radiation transmit the impulses from the LGB to the visual cortex in the occipital lobe of the brain.
The visual cortex is the last step in the optic pathway.
It processes the information sent from the retina
Loss of vision due to pressure build in the fluid of the eye.
Puts pressure on optic nerve.
Open-angle: Slower rate of progress; patients may not notice they have lost vision until the disease has progressed significantly.
Closed-angle: Appears suddenly and is often painful; vision loss can progress quickly, patients often seek medical attention before permanent damage occurs.
Second leading cause of vision loss worldwide.
Usually occurs in older adults.
Results in loss of vision in the center of the visual field and spread of the outer side of the eye.
Symptoms: Blurred vision, optical hemorrhages, shadows or missing areas of vision, slow recovering of vision after exposure to bright light.
Clouding of the lens leads to a decrease in vision.
Lens obstructs light from passing and being focused on the retina.
Most common cause of blindness.
Treated with surgery.
Commonly due to aging.
Can also be an effect of trauma, radiation such as UV light, genetics, skin diseases, and drug use.
Reduction of vision.
A glare in their vision.
Why and How We See What We See
Why Does This Happen?
This grayscale image is processed through your rods. The illusion is created because of your out-of-consciousness processing system at work.
Your eyes automatically sharpens the contrast of the edges of surfaces to make it easier to divide objects from their backgrounds.
The illusion of black dots was created in an effort for your eyes to simply separate the white lines from the black background.
How Rods Respond To Light
3 Main Parts:
Rhodopsin- Contains the proteins opsin and cis-retinol.
Transducin- Made up of 3 subunits.
Phosphodieterase = PDE. Has 2 inactivated alpha units attached to it. You want them to be detached so that PDE can activate.
Light hits Rhodoposin.
When light touches Rhodopsin, Cis-Retinol changes into Trans-Retinol, a different form of the molecule.
This causes Trans-Retinol to lose its attraction for the Opsin molecule, and once that connection breaks, the Retinol leaves and it exposes a binding site on the Opsin.
*Pay close attention to the GDP and you'll notice something different in the next step.
Opsin then goes over to Transducin, since the binding site is exposed it can catalyze a reaction. Transducin converts its GDP to GTP.
GDP- 2 Phosphate Groups.
GTP- 3 Phosphate Groups
The GTP subunit is activated and leaves the other two subunits behind. It goes over to the alpha subunit of the PDE.
When GTP attaches to one of the alpha units it is removed from the PDE. This process has to happen a second time for the other alpha unit to be removed.
*After both alpha units are removed PDE can do its job which is to convert cyclic GMP to GMP. This leads to vision and how we are able to detect light.
Are tile A and B the same color?
How is that possible?
When your brain attempts to determine the color of an object, it knows that shadows will make an object appear darker than it actually is.
To compensate, our brains interpret the image as being lighter than how they appear to the rods in your eye.
Therefore, tile B appears lighter to you because it is under a shadow while tile A is not.
Are the horizontal lines parallel to one another?
Different types of neurons react to how we see dark and light colors.
Parts of the gout lines (the lines in-between the tiles) are dimmed or brightened in your retina.
The gradient creates an illusion that the black and white tiles are moving towards each other, almost as if they were moving.
2) 120 million
6) lateral geniculate body
7) the visual cortex
8) occipital lobe of brain
9) glaucoma, macular degeneration, cataracts
Historic First Images of Rod Photoreceptors in the Living Human Eye
The Optical Society
By: Lyndsay Meyer
08 June 2014
Tiny light-sensing cells known as rods have been clearly and directly imaged in the living eye for the first time. Scientist can now see through the murky outer layer of the eye, making it so they can now see the cellular structure of the eye. Being able to see the eye more clearly will help doctors diagnose degenerative eye disorders faster with quicker symptom detection and give more effective treatments treatments. This new breakthrough of a non-invasive adaptive optics imaging system allows scientists to see down to just one rod in the eye. This allows us to study a whole new class of blinding disorders on the retina.
cGMP-gated channels will close.
Sodium does not enter into the rod.
Neurotransmitters are not released.
Receptor potential becomes negate until it reaches equilibrium potential for potassium ions. It goes back up to its level when there is no more stimulus.
Depolarization cGMP to GMP
*When there's no stimulation(light) the opposite happens.
The Visual Cortex
The cells of the magnocellular and parvocellular layers project all the way to the back of the brain to the primary visual cortex (V1).
V1 cells are organized in different ways:
First they are arranged retinotopically, which means that a point-to-point map exists between the retina and primary visual cortex, and neighboring areas in the retina correspond to neighboring areas in V1.
This allows V1 to position objects in 2D of the visual world.
In V1 by comparing the signals from both eyes the 3D depth is mapped out. Those signals are processed in a stack of cells called Ocular Dominance Columns. A slight discrepancy in the position of an object relative to each eye allows depth to be calculated by triangulation.
Finally, V1 is organized into orientation columns, stacks of cells. They can detect the edges of objects in the visual world, so they have the task of visual recognition.