Lecture 8 - Vision Flashcards
Where is the 3rd order neuron located along the visual pathway?
lateral geniculate nucleus of the thalamus
What are the 3 layers of the eyeball?
- sclera
- choroid
- retina
The sclera is continuous to the _____ _________
dura mater
What is the choroid?
a deep plexus of blood vessels like the choroid plexus deep to the sclera
What is the most inside part of the eye?
the retina
What does the conjunctive do?
fixes eyeball against our eyelid, part of the sclera
- is a connective tissue
What is the limbus?
boundary of cornea and sclera
What is the ora serrata?
the end of the retina, not smooth
- about 2/3 of the eyeball posteriorly
What is the lens?
a transparent layer of proteins, divides eyeball into anterior and posterior chambers
What is in the anterior chamber of the lens?
pigmented cells, secrete fluid drains into anterior chamber = aqueous humor
What is in the posterior chamber of the lens?
like glass, vitreous humor secreted by non-pigmented epithelia in the cell body
What happens when aqueous humor drainage is blocked?
glaucoma (other causes too)
What eye structures work on focusing and refraction of light?
cornea and lens
What eye structures work on brightness and quality?
iris and retina
What is the shape of the cornea?
convex anteriorly
What is the cornea for?
gross adjustment
What shape is the lens?
biconvex
- anterior convexity is adjustable
What is the job of the lens?
fine adjustment
What is a cataract?
layers of proteins that are transparent degrade with age so the transparency compromised
What happens with ciliary muscle contraction?
increases anterior convexity
- with CLOSE objects
- zonula fibers pull the lens out, build up biconvexity
What happens with ciliary muscle relaxation?
the anterior convexity is decreased
- with FAR AWAY objects
- relaxes ciliary muscles, pulls zonula fibers, stretches the anterior part of the lens
- more flat not so convex
What gives the pinhole effect?
the PUPIL
What two muscles control the dilation of the pupil?
- pupillary dilator/dilator pupillae
- pupillary sphincter/constrictor pupillae
What innervates the pupillary dilator?
sympathetic: superior cervical ganglia
What innervates the pupillary sphincter/constrictor?
CN III: ciliary ganglion
What does the retina do with strayed light?
absorbs it!
- reflection goes into the vitreous body, too much can cause you to not be able to see anything
- this absorbs light to get a clear image
What are photoreceptors?
rods and cones
NOT NEURONS
What do rods see?
black and white
What do cones see?
blue, red, and green
What is unique about the projection direction and processing direction of light?
opposite
What are bipolar neurons?
1st order neurons!
What is the ration of rods to bipolar neurons? Why is this important?
15~30:1
- helps with gross image
What is the ratio of cones to bipolar neurons? Why is this important?
1:1
- acuity!
What are ganglion cells?
2nd order neurons
What do cones/rods release?
glutamate
INHIBITORY!!!
What do pyramidal cells release in the cerebral cortex?
glutamate/aspartate
EXCITATORY
What happens when glutamate is released in the eyes?
it inhibits functions of the bipolar neuron
What is the macula?
part of the retina
- lateral to the optic disc
- around 5.5 mm diameter
What can happen in the macula that can cause legally blindedness?
macular deceneration
- cones died, acuity lost
- can see things just without detail
What is the fovea?
center of the macula in the retina
1.5mm diameter
What is the foveola?
part of the fovea, very small 0.15mm diameter
What is unique about the foveola?
- cones only, highest visual acuity
What is foveation?
fixes the fovea on the target objects
What does the ganglion cell axon bundle form?
the optic nerve
What is the blind spot?
has no photoreceptors
- happens worse with a retina injury/stroke
What is the visual pathway to the V1?
left optic nerve to optic chiasm to left optic tract to left latearl geniculate
What axons form the left optic nerve?
both nasal and temporal
What happens with the axons at the optic chiasm?
crosses over (axons)
What are the axons doing at the left optic tract?
temporal and nasal axons run together
What is the lateral geniculate?
3rd order neuron in the thalamus, projects to V1
What is the parallel process?
pathway through thalamus mainly for us to not see something but still perform
- such as reaching for a bottle you know is there but not looking up to grab it
What is the geniculostriate pathway?
lateral geniculate nucleus to V1
- STRIPED, the mitochondria show up as stripes with staining
What makes up the 2 parts of the geniculostriate pathway?
- superior projection fibers in the parietal lobe for the inferior quadrant
- inferior projection fibers in the temporal lobe, Meyer’s loop for the superior quadrant
What projects to 60% of posterior V1?
Macula
What is the retinotopy?
spatial information conserved
- presentation of the world in your mind
How is the iris controlled by visceral motors when sunlight is too strong?
sphincter pupillae activated by CNII, decreases light into the eyeball
What are the visual hemifields?
each eye has a right and left component
Where is the temporal space?
in the nasal retina
Where is the nasal space?
in the temporal retina
What is the binocular field?
crossover of the left and right hemifields when looking forward
What is the optic nerve responsible for?
the vision of the eye, ipsilateral nasal and temporal retinas
What happens at the optic chiasm?
decussation or crossover of bilateral nasal retina tracts
What happens at the optic tract?
vision of both visual hemifields
- ipsilateral temporal and contralateral nasal retina
If there is an impairment at the optic nerve what happens?
blind of the eye: CN II
What happens if there is an impairment at the optic chiasm?
tunnel view: optic chiasm
What happens if there is an imparment at the optic tract?
homonymous hemianopia
What happens if there is an impairment on the optic radiation?
superior quadrantoanopia: Myer’s loop
What happens if there is an impairment at the geniculostriate pathway?
homonymous hemianopia
Where do the parallel projection pathways go through?
not through the thalamus
What are parts of the tectopulvinar pathway?
- pretectal area and superior colliculus
- pupillary light reflex
- visual association area: dorsal stream
What happens if there are issues with the dorsal stream?
blindsight/riddoch’s phenomena
- pts with an occipital stroke cant see one side
What is in the hypothalamus in the parallel projection pathway?
suprachiasmatic nuclei
What does the suprachiasmatic nuclei do?
relay for circadian rhythm
Is CNII afferent or efferent? Where does it go in the pupillary light reflex pathway?
afferent, specific ganglion cells, NO PHOTORECEPTORS
- to bilateral CNIII parasympathetic nucleus
Is CNIII efferent or afferent? What does it do?
efferent
- constricts bilateral pupils
What happens if you shine a flashlight in one eye and it constricts but the other does not?
the CN III on the side that doesnt constrict is nonfunctional
What happens when one the flashlight is shined into one eye and both pupils constrict, then into the other and they dilate?
on the side that the flashlight causes to dilate CN II is nonfunctional
Axon bundles from which side of the nasal and temporal retina are in the left optic nerve, optic chiasm, and right optic tract?
- left optic nerve: both left nasal and temporal retina
- optic chiasm: bilateral nasal retina ganglia axons
- right optic tract: right temporal and left nasal retina ganglion axons
