Eye structures Flashcards
Where does object procession happen?
In the ventral “what” stream. This passes through the temporal lobe
Where does spatial processing happen?
In the dorsal “where” stream through the parietal lobe.
Where to both the spacail and object processing stream come from and go to?
Both come from occipital lobe that recieves visual input and they take their individual streams to the frontal lobe.
What do sensory receptors sample?
small amounts of energy from the environment
How does CNS do with sensory info?
processes and forms an internal representation of external and internal world.
Why would CNS use feedback to regulate receptors and sensory activity at all levels?
To maintain a tolerable range of sensory stimulation
Three coats of eyeball
fibrous coat, vascular coat, nervous coat
What parts make up fibrous coat of eye?
Sclera, dense white CT and Cornea which is transparent
What part of epithelium reduces spread of infection?
Bowmans basment membrane
What makes up outerlayer of cornea?
stratified squamous epi
what is the corneal stroma?
Below the epithelium, it has fibroblast that make lamellae of collagen fibers
what is the basement membrane of corenal epithelium called?
descemets membrane
what is on the inner surface of cornea?
Simple squamous endothelium that transfers nutrients from aqueous humor to cornea
Where do corneal epithelial cells come from?
adjacent corneosclera limbus
how is the DNA in the cornea protected from UV?
nuclear ferritin
what the corneal epithelia stem cells called?
transient amplifying cells, TAC
What holds lense in place?
suspensory ligaments
what are the fibers called that attach and hold lense in place?
Zonule fibers
Where do zonule fibers extend from?
ciliary body
What maintains the resting convexity of lense?
outward pull of suspensory ligaments from ciliary body when muscle is relaxed with intrinsic elastic fibers
What do intrinsic elastic fibers of lens cause?
inherent tendency to bulge or increase the convexity of lense
what is the outer capsule of lenes made of?
elastic collagen IV and glycoproteins
what produces new lens cells?
germinal zone around outer edge of lens
what happens to new lens cells as they migrate away from germinal zone?
they lose their nuclei so that they are transparent
presbyopia
far sightedness, can see clearly far away
what causes presbyopia
loss of elasticity in lense, not weak eye muscles
what is implicated in cataracts?
oxidative damage may be causeing lense to become obaque
what type of vision does lense need to be the most convex?
for close up vision
What is it called when ciliary muscle changes convexity of lens?
accomidation
How does ciliary muscle relax tension on suspensory ligaments?
By contracting they relax ligaments enabeling close up vision
does close or far light diverge more?
nearby light diverges more and requires greater refraction to hit the right spot on retina
what determines ultimately where the lense focuses light?
the length of the eyeball,
long eyeball causes what?
Myopia, near sightedness, retina
short eyeball causes what?
Hyperopia, far sightedness
Where is light focused in hyperopia?
light is focused beyond retina
Where is light focused in myopia
light is focused before retina
Where is aqueous humor located?
anterior and posterior chamber
What absorbs humor into venous system?
schlemms canal , ouside edge of cornea
What can cause glaucoma?
poor schlemms canal drainage or over production of humor
What can block flow out of schlemms canal?
adherence of iris to lense that blocks flow
What structures does iris contain?
pigmented striations of CT, blood vessels and smooth muscle
What is the stroma of the iris?
CT with melanocytes
What type of muscles does iris have? 2
constrictor and dilator pupillae
Where is pigment epithelium located in iris
continuous on posterior surface of iris, it doesn’t allow any light in.
what light gets scattered more red or blue?
Blue gets scattered more (atmosphere, eye bits)
what determines color of eye if all pigment is brown?
the pattern of light refraction by melanin
What causes blue eyes?
Deep pigment scattered by the stromal layer refraction of blue light
Why is melanin brown?
it absorbs blue grean and reflects black yellow and red
What system controls the sphincter pupillae?
parasympathetic - it constricts pupil
What system controls the dialator pupillae?
syspathetic, opens pupil to allow more light
what does pupil size determine in addition to regulating light intensity?
determines focal range,
What does smaller pupil do to range of focus?
small pupil increases range of focul
Where does the parasympathetic neurons to eye travel from?
CN III the ocular motor nerve
Where is the ciliary ganglion for eye?
near posterior surface of eyeball
Where does sympathetic nerves for eye come from?
superior cervical ganglion that has postganglionic neeurons that project axons along arteries to iris
what does parasympathetics do to eye?
constrict pupil and contract lense
where are the preganglionic neurons located for parasympathetics to eye?
Edinger whestphal nucleus
What do the post ganglionic neurons in the ciliary ganglion activate? 2
sphincter pupillae and ciliary muscle to contract lense (relax fibers)
What is the purpose of the pupillary light reflex?
maintain homeostatic levels of light entering eye
what cells in retina respond to ambient light?
melanopsin ganglion cells
what do the melanopsin ganglion cells activate?
pretectum and edinger Westphal nuclei in brain
What coordinates both eyes?
Pretectal nucleus of midbrain
What does the pupillary light reflex look like?
reflexive constriction of both pupils in response to light shone in eyes.
path of pupillary light relfex?
light, melanopsin ganglion cells, pretectal n. EW nucleus, ciliary ganglion, pupil constricion
Preganglionic neurons from where innervate superior cervical ganglion cells
Preganglionic neurons are from T1 and T2
What two things do the postganglionic neurons activate?
Dilatory pupillae and tarsal muscle to raise eyelid
the postganglionic neurons that innervate superior cervical ganglion are from what system?
sympathetic
What type of reflexes control iris and upper eyelid?
local sympathetic reflexes with influence from limbic system
when would limbic system and hypothalamus influence local reflexes of iris?
during emotional state.
what is the function of the tarsal muscle
to raise eyelid in emotional states - sympathetic
what would damage to part of sympathetic NS cause to happen to eye area
drooping eyelid, horners syndrome.
what causes floaters?
age related, collagen fiber bundles that cast shadows
what is vitreous body made of>
hyauronic acid and type II collagen, 99% water
what is the eyeball derived from?
the embryonic brain
what forms lens placode?
ectoderm from the neural tube, not neural tissue
What are the neural and pigmented layers of retina derived from?
optic vesicle
neural layer
neruons and photoreceptors
pigment layer
retinal pigment epithelium RPE
What is outer layer of eye derived from?
meningeal tissue
what nourishes vitreous body and lense in embryo?
hyaloid artery
