Intro and Duplex (Midterm I) Flashcards
What are the main reasons that the optic nerve is more like a tract of the CNS than PNS?
- development from diencephalon
- myelin produced by oligodendrocytes
- vasculature with blood-retinal barrier
- narrow and completely ensheathed retinal synapses
- regeneration is rare
What are the three principle functions of the retina?
- transduce visual images to electrochemical signals
- perform initial processing of signal
- convert signal into signal to be sent and interpreted by brain
What is the order of layers in the retina from anterior to posterior?
- inner limiting membrane
- nerve fiber layer
- ganglion cell layer
- inner plexiform layer
- inner nuclear layer
- outer plexiform layer
- outer nuclear layer
- outer limiting membrane
- photoreceptors (rods and cones)
- retinal pigment epithelium (RPE)
What are specialized glial cells that span nearly all of the retinal layers? 1. What do they form? 2
- muller cells
2. OLM and ILM
What cells convert light energy into an electrical signal?
photoreceptors
What cells receive visual info from photoreceptors and transmit this signal to retinal ganglion cells?
bipolar cells
What cell are the output neurons of the retina?
ganglion cells
What are the retinal neuron cells that modulate the transmission between the photoreceptors, bipolar cells, and ganglion cells?
horizontal and amacrine cells
Why does the optic nerve have a white look?
RGC axons become myelinated as they pass the lamina cribosa
What is it called when RGCs become myelinated before reaching the ONH? 1. What is the effect on vision? 2
- MRNF
2. none
Where do ganglion cells from the retina project to? 1. What is this collection of axons called? 2
- lateral geniculate nucleus (in thalamus)
2. optic nerve (before optic chiasm) and optic tract (after optic chiasm)
Where do cells of the lateral geniculate nucleus project to? 1. What is this collection of axons called? 2
- primary visual cortex
2. optic radiations
What portion of the axons from the retina cross at the optic chiasm?
the axons from the nasal retina
What is the name for the optic radiations that loop temporally around the lateral ventricle and synapse below the calcarine fissure? 1. What area of the visual field are these from? 2.
- Meyer’s loop
2. superior visual field (inferior retina)
Does the superior or inferior visual field have a more direct route to synapse from the LGN to the primary visual cortex?
inferior field (superior retina)
What is the detection of a stationary light target displayed on uniform white background called?
static perimetry
What is the main indication of a prechiasm lesion?
visual field defect that crosses the midline
What kind of visual field defect is associated with damage to Meyer’s loop radiations?
superior quadrantanopia
What kind of visual field defect is associated with damage to non-Meyer’s loop radiations?
inferior quadrantanopia
Where is the lesion locate is there is a homonymous hemianopia with macular sparing?
at the calcarine fissure or striae cortex
What anatomical finding is responsible for a junctional scotoma when there is a pituitary adenoma?
knee of Willebrand
What is a clear sign in a visual field that a lesion has occurred prechiasmally?
defect crosses the midline
Where do the thermal and chemical injuries occur on the retina with intense sun exposure?
outer retina (bilateral)
For scotopic vision: what are the photoreceptors that mediate this? 1. Are threshold detection levels high or low? 2. Is it associated with good or poor visual acuity? 3. Is there a high or low amount of saturation? 4
- rods
- low (more sensitive)
- poor VA
- high saturation at high luminances
For photopic vision: what are the photoreceptors that mediate this? 1. Are threshold detection levels high or low? 2. Is it associated with good or poor visual acuity? 3. Is there a high or low amount of saturation? 4
- cones
- high (less sensitive)
- good VA
- little saturation
What are the photoreceptors that mediate mesopic vision?
rods and cones
Where does visual pigment reside in the photoreceptor? 1. What is its responsibility? 2
- discs in outer segment
2. capturing photons
Do cones or rods have encapsulated discs in the outer segment?
rods
Where is visual pigment first formed? 1. What area does the pigment pass to end up in its final location? 2
- inner segment
2. cilium
About how many rods are there in a human retina? 1. How many cones? 2
- 120 million
2. 6 million
What is the cause of the foveal light reflex?
concave shape of fovea
What is the location of the axon terminals of the pushed aside cones in the fovea called?
Henle fiber layer
What is the retinal vasculature found in the fovea?
there is none
Human vision is capable of operating over a large range of light intensities. Of the roughly 11 log units that this range encompasses, how much range of adaptation is due to pupil constriction?
1 log unit
