L4: The Visual system: Retinal Processing Flashcards
What is the path of light through the human eye?
Into the eye, thriugh the lens, through the vitrous humor, onto the retina and to the optic nerve
Where does perception of visual stimulus happen?
The retina
What is accommodation?
Changing the shape of the lens to accommodate near vs far
What controls accomodation?
Ciliary muscles and zonule fibers
What happens to the lens during far vision?
The ciliary muscle relaxes, and zonule fibers (suspensory ligament) contracts which flattens the lens
What happens to the lens during near vision?
Ciliary muscle contracts, suspensory ligament relaxes which makes the lens globular.
What is:
1. Emmetropia?
2. Myopia?
3. hyperopia?
- Normal vison: lens can accomodate
- Nearsighted: lens brings image together too quickly
- Farsighted: lens cant bring images together
What is the region of highest visual accuity?
Fovea
Where is the blind spot?
Optic Disk
What is around the fovea?
The macula
What is the visual field?
What you’re actually looking at in space
What is the retinal field?
How the info is being projected onto the retina
What color is in the visual field of the left eye:
1. Superior temporal quadrant?
2. Inferior temporal Quadrant?
3. Superior Nasal quadrant?
4. Inferior Nasal quadrant?
- Green
- Purple
- Yellow
- orange
What color is in the retinal field of the left eye:
1. Superior temporal quadrant?
2. Inferior temporal Quadrant?
3. Superior Nasal quadrant?
4. Inferior Nasal quadrant?
- Orange
- Yellow
- Purple
- Green
What color is in the visual field of the right eye:
1. Superior temporal quadrant?
2. Inferior temporal Quadrant?
3. Superior Nasal quadrant?
4. Inferior Nasal quadrant?
- Yellow
- Orange
- Green
- Purple
What color is in the retinal field of the right eye:
1. Superior temporal quadrant?
2. Inferior temporal Quadrant?
3. Superior Nasal quadrant?
4. Inferior Nasal quadrant?
- Purple
- Green
- Orange
- Yellow
What is the binocular and monocular field of vision?
Binocular: Place where both eyes see
Monocular: Place where one eye sees (usually peripheral vison)
If the optic Nerve is damaged before the optic chiasm, what will happen to my visual field?
I will lose vision in one whole eye on the same side as the injury.
If the optic nerve is damaged after the optic chiasm where will I lose vision?
In one visual field in each eye.
Where does my left field of vision come from?
Left nasal and right temporal.
Where does my right field of vision come from?
My right nasal and left temporal.
What are the:
1. Two types of photoreceptors?
2. 4 types of retinal neurons?
- Cones and Rods
- Horizontal cells, bipolar cells, Amacrine cells and ganglion cells
What is the path of light into the retina?
- Into the retina to the photoreceptors
- from photoreceptors to ganglion cells
- Ganglion cells out of eye
Why are photoreceptors embedded into the epithelium?
So they can be taken up and recycled because they get damaged from light.
What is rhodoposin?
The chemical in rods that absorbs light
When do rods fire APs?
In darkness
What happens to rods in light?
Na channels are closed and rods hyperpolarize and glutamate is not released.
1 photon activates:
How many transducin molecules?
Which closes how many Na channels?
500
250
What is the role of vitamin A in vision? Where is it stored?
Vitamin A is used to help make new proteins so that the eyes can stay light-sensitive. It is stored as retinol in the liver.
What happens to kids in places where vitamin A-rich food is not available?
They have bad night vision.
What is the difference between rods and cones?
Rods have bigger photo optic disks to be more sensitive. But have only one opsin.
Cones have multiple opsins which allow them to be color sensitive.
What is the ganglion response of the bipolar cell to light?
During light, the cone cell is hyperpolarized and does not produce glutamate. This increases mGLU activity in the on-center bipolar cell which is activated.
What is the ganglion response of the bipolar cell to dark?
The AP is fired from the cone cell which activates the NMDA receptor with glutamate on the off-center bipolar cell which activates the off-center ganglion cell.
What type of receptor is an NMDA receptor? mGLU?
Ligand gated, GPCR
In on-center receptors, what is the result of light stimulation?
Increased firing rate
In off-center receptors, what is the result of light stimulation?
decreased firing rate
What type of photoreceptors are found closer to the fovea?
cones
What kind of photoreceptors are foud closer to the temporal and nasal eye?
Rods
What is spacial resolution (acuity)?
How close objects can be and youre still able to telll them apart. Small receptive field= more detail
What are the units of luminance and what is it measuring?
Candela/unit area
Amount of brightness
What is:
1. Scototopic vison
2. Mesotopic vison
3. Phototopic vison
- In the dark when only rods are used
- Moonlight when rods and cones are used
- Indoor lighting when mostly cones are used and when there is best visual acuity.
How do cones see color?
They have multiple opsins which compare wavelengths to each other when they absorb light to detect what color is being seen.
At what color do rods have the best acuity?
Blue/purple
What is:
1. Trichomat
2. Protanopia
3. Deutranopia
- Normal color vision with all 3 opsins (blue, green, red)
- Missing red opsin
- Missing green opsin
What is the purpose of electrical synapses in the retina?
To be sensitive to things moving quickly.
What type of NT do rods and cones release?
Glutamate
What type of NT do bipolar cells release?
Glutamate hich excites ganglion cells
What NT do horizontal cells release?
GABA
What is the purpose of horizontal cells?
When there is dark surround, the center cone is inhibited which enhances center response.
What is the purpose of horizontal cells?
When there is a dark surround, the center cone is inhibited which enhances the center response. When there is light in the surround, the center is inhibited.
What NT do amacrine cells release?
GABA, Glycine and dopamine (all inhib)
What is the role of connexin 36?
gets rid of lateral inhibitory gap junctions.
What cell controls information flow to the brain?
Retinal ganglion cells (RGC)
What is a retinal prosthetic lens and how does it work/
It’s a computer chip that is inserted into the lens to compensate for a bad retina and transmits signals to the optic nerve. Everything after that is processed as normal.
What is a retinal prosthetic retina and how does it work/
Its a battery operated wire that acts as a transmitter from the retina to the optic nerve.
What is a cortical prosthetic?
goes from the optic nerve and is an electrode array that does the work of the visual cortex to signal the rest of the brain.
What are some obstacles to eye prosthetics?
Regrowth of nerves and degeneration of devices.
