Vision Flashcards
What is comprised of the fibrous tunic?
cornea
sclera
What is part of the vascular part of the eye? “uvea”
choroid
ciliary body
iris
What is the nervous tunic of the eye called?
retina
What is the blind spot of the eye called?
optic disc
What is the densest part of the retina?
fovea centralis
What 2 things comprises the retina?
optic disc
horizontal visual streak
Light is _____ as it passes through the cornea and lens
refracted
The [cornea/retina] refracts more light than the lens
cornea
What fine-tunes the image?
lens
When the lens becomes [rounder/thinner], it increases refraction for near vision
rounder
What is the accommodation of the lens?
refracting more or less in the lens to see near of far
When the lens becomes [rounder/thinner], it increases refraction for distance vision
thinner
List the layers of the retina from superficial to deep
pigment cell layer
photoreceptor layer
outer nuclear layer
outer plexiform layer
inner nuclear layer
inner plexiform layer
ganglion cell layer
optic nerve layer
What is the pigment cell layer of the retina?
absorbs light
prevents light from scattering between photoreceptors
convert TRANS-retinal to CIS-retinal needed by photoreceptors
What is the photoreceptor layer?
outer portion of rods and cones that contain light-sensitive components
What is the outer nuclear layer?
cell bodies and nuclei of rods and cones
What is the outer plexiform layer?
synapses of photoreceptor cell axon terminals with dendrites of retinal interneurons (bipolar and horizontal cells)
What is the inner nuclear layer?
cell bodies of retinal interneurons
- Bipolar cells (B)
- Horizontal cells (H)
- Amacrine cells (A)
What is the inner plexiform layer?
synapses of retinal interneuron axon terminals with dendrites of ganglion cells
What are the output cells of the retina?
ganglion (G) cells
What is the ganglion cell layer?
cell bodies of ganglion cells
output cells of the retina
What is the optic nerve layer?
axons of ganglion cells traversing the inner retina on their way to the optic disc —> optic nerve
Where is the tapetum lucidum found?
choroid
What is the tapetum lucidum?
reflective layer in the choroid that increases light detection in dark conditions
T/F: Retinal pigment epithelium lacks melanin overlying tapetum
true - allows light to pass through and reflect back to stimulate photoreceptors
may decrease acuity
[Rods/Cones] are used in scotopic vision.
rods
What do the outer segment of rods contain?
contains photopigments specialized to absorb light
What is rhodopsin? It has a [high/low] threshold
absorbs light
low
What does rhodopsin contain in combination with opsin, a G-protein coupled receptor?
retinal (vitamin A derivative)
What does the outer segment of cone cells do?
tapers
Cones have ______ and _____ which have a higher threshold.
photopsins
lodopsins
Many domestic animals have ____ types of cones, which are composed of ______ in combination with a different type of opsin.
2
retinal
What is phototransduction?
light converted to electric signal
cis —> trans, changes shape of G-protein
PDE degrades cGMP
cGMP gated Na+ channels close
hyper polarize the cell and decrease glutamate release
In the dark, rhodopsin contains [cis/trans]-retinal, but with light absorption, it causes transformation to [cis/trans]-retinal which dissociates from opsin aka a “________”
cis
trans
bleaching reaction
After bleaching ____ must be rebuilt for the rod to function
rhodopsin
T/F: Rods function well in bright light
FALSE
What is the first order neuron for the retinal pathway?
bipolar cell
List the interneurons of the retinal pathway
bipolar cell
amacrine cell
horizontal cell processing
List the 2nd order neuron
ganglion cells
_____ work best in dim light/dark conditions
Rods
Many _____ converge on one bipolar cell
rods
What is MORE likely to be activated by low levels of light due to convergence of rods
bipolar cells
What is the 3rd order neuron for the pathway for conscious perception of vision?
lateral geniculate nucleus in thalamus
“sub-cortical”
Where do axons for the LGN go?
visual cortex in occipital lon
visual association areas parietal and temporal lobes
Each visual field represented in the [ipsilateral/contralateral] optic tract
contralateral
The closer together the eyes are, the [more/less] input each eye gets from BOTH visual fields
more
Horses have [more/less] decussation which allows for a greater field of vision
more
Increased medial eye placement —> increased binocular vision overlap —> [increased/decreased] decussation at optic chiasm
decreased
T/F: Visual input that crosses the midline before entering the eye does NOT need to cross the midline again
TRUE
What is the pupillary light response? What percentage of fibers of to the midbrain protextal nucleus and so on?
moves to rostral colliculus —> accessory oculomotor nucleus —> ciliary ganglion —> pupillary sphincter (parasympathetic)
BYPASSES the LGN
20%
PLR is a ______ reflex inducing [sympathetic/parasympathetic]-induced pupil constriction
subcortical (midbrain)
parasympathetic
Does having a pupillary light response mean you have conscious perception of vision?
NO - you could be blind in one eye and still have a pupillary light response
What is anisocoria?
having different sized pupils
Trace the menace response pathway
retina —> optic nerve —> optic disc —> optic tract —> visual cortex (lateral geniculus and rostral colliculus) —> facial motor nucleus —> facial n. in medulla —> auriculopalpebral n.
What does subcortical mean?
midbrain
doesn’t go all the way to the cortex
What does cortical mean?
goes all the way to the cortex
The menace response is a [cortical/subcortical] response pathway
cortical
What is the vestibulo-ocular reflex?
initiates compensating eye movement to keep vision fixed when head turns
What nerves are involved in the vestibulo-ocular reflex?
CN 3, 4, 6
Where is the vestibulo-ocular reflex found?
medial longitudinal fasciculus
What is the visual startle reflex?
rostral colliculus (tectum) in midbrain
decussates
descends cord in tectospinal tract
contraction of neck muscles to turn toward stimulus
