Visual Part 2 Flashcards
What is the fovea centralis? What are two properties of it?
Central focal point of the retina. Has only cones and high acuity
What structures doe light pass through before it hits the retina?
Cornea, aq. Humor, lens, vitreous body
What is the macula lutea? Why is it yellow?
Yellow area surrounding the fovea. Pigments from carotenoids and lutein and zeaxanthins absorb UV light, protecting the retina from oxidative damage
Where does the central artery of the retina come from?
The internal carotid artery
What are the four retinal layers- from outer to inner layers
Pigmented epithelium, photoreceptors, neural cells, ganglion cells
What are three types of neural cells?
Bipolar, horizontal and amacrine cells
What pigment is in cones?
Iodopsin
What pigment is in rods?
Rhodopsin
What part of the neural layer releases glutamate?
Inner segment of the photoreceptors
Where are pigments located within the photoreceptors?
Vesicular discs
How does light affect a photoreceptor cell?
11cis retinal –> trans retinal–>opsin activates PDE–> PDE reduces cGMO activity –> cell hyperpolarized–> less glutamate is released
What does photopic mean? Which photoreceptors are photopic?
Vision in bright light/ low sensitivity (cones)
What is scotopic? What photoreceptors are scotopic?
Vision in dim light/ low sensitivity (rods)
Which photoreceptors are chromatic? Which photoreceptors are achromatic?
Cones are chromatic, rods are achromatic
Which photoreceptors are better to detect visual motion?
Rods
Which photoreceptors are high acuity, sensitive to direct light and impart good spatial resolution?
Cones
Which photoreceptors have low acuity, are sensitive to scattered light and impart poor spatial resolution?
Rods
What photoreceptors are primarily in the periphery of the retina? Which are primarily in the fovea?
Rods are primarily in the periphery. Cones are primarily in the fovea, but can be spread out thinly in the periphery for general color vision
What is one way that cones increase vision acuity in the fovea centralis?
Each cones activates a single ganglion
Why is the choroid layer of blood vessels behind the retina?
Because light cant pass through blood vessels well
How is it that light can pass through the ganglion and bipolar cells before hitting the retina?
They have the same refractive index as the vitreous humor
What are six functions of the retinal pigmented epithelium?
- visual acuity (limit reflection of light) 2. pigments absorb blue/UV light, as antioxidants 3. recycling of 11-cis retinal to maintain photoreceptor excitability 4. transportation of nutrients/waste from photoreceptors and choroid 5. phagocytosis of UV damaged photoreceptors 6. secretion of PEDF and VEGF
What can happen if the RPE no longer phagocytoses photoreceptor fragments?
fragments accumulate and separate from the choroid, causing anoxia and cell death. retinitis pigmentosa
How do cells in the fovea centralis get their nutrients?
its avascular, but nutrients are acquired by active transport to and from the choroid- transporters are in the RPE
