PSYA01H3 Lecture Notes - Ganglion Cell Layer, Aqueous Humour, Optic Disc

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24 Nov 2012
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PSYAO1 Notes:
VISION
Eye and its Functions
Means of Protection
- enclosed within bony slot
- eyelid - cover from dust and dirt
- eyebrow - inhibiting sweat from exposing open eye
- reflex mchsms
- upon obj. hitting face or surface of eye, they activate
- cause eyelid to close automatically, head withdrawl
Eye Anatomy
- Cornea: eye tissue; transparent, covers eye's front side
- "bulge" that allows in light
- fixed shape
- Sclera: outer eye layer; tough, "whiteness" of eye
- rest of eye covered by this
- Iris: muscle; shows a pigment phenotype, controls pupil size
- double muscle band that controls amt of light allowed in
- adjustment thro. dilation/constriction depending on light conditions in
environmt.
- dark (=dim): dilate (stretch) eye
- bright: constrict (tighten) eye
- Aqueous humour: fluid that fills region right behind cornea
- tissue behind cornea constantly prod. this
- removes the fluid from blood & gets it to this eye region
- provides nutrients for cornea and other frontal parts of eye
- circulation and renewal key for using this fluid effectively (ex. cornea req.
it for it to remain transparent)
Diagnosed with Glaucoma!
Why? Eye disorder (vision dmged) by
a) rapid prod. of aqueous humour
b) clogging of passageway that returns aqueous humour to blood
=> exposed to too much pressure by high [] of aq. humour w/in eye.
- Lens: transparent organ behind iris; facilitates img focus on retina
- way in which lens and cornea curved makes imgs focus on inner surface
at eye's back region (=retina)
- incoming imgs reversed in both up/down and left/right, but brain able to
make up for this and interpret info. properly.
- right behind iris
- comprised of no blood vessels b/c must remain transparent
- dead tissue
- Lens:
- flexible
- thus able to accomodate: special group of muscles able to
alter its shape to make it compatible for eye to obtain imgs of
those obj's either near or close
Vision Problems
- Normal conditions:
- matching of eye length w/ bending of light rays created by
cornea & lens
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- allows for incoming img to focus sharply on retina
- Problem?
- immatching of eye length w/ bending of light rays
- retina = out of focus
-> Sightedness problems
[eye status; artifical lens req. to refocus img]
- NOTE: artifical lens
(ex. eyeglasses, contact lenses)
- farsightedness
- too long
- concave lens
- nearsightedness
- too short
- convex lens
- natural (coming from aging)
- lens losing flexibility
- harder to focus on imgs closeby
- reading glasses + convex lenses
OR bifocals + glasses
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- Retina - tissue; loc. at back internal eye surface, holds the photoreceptors
(receptive cells) & other neuron groups that assoc. w/ them.
- performs sensory fcns of eye
- holds >130mil photoreceptors
- Photoreceptor - visual receptor cell in retina (=rod/cone)
- special neuron group doing transduction
[light -> neural.E]
- send info to neurons that fire their axons towards optic disc
- Optic Disc - circle-shaped structure; back of eye
- one end of eye from retina where axons depart from eye and join
up w/ optic nerve
- optic nerve sends info to brain
Blind spot
- apparent b/c no photoreceptors placed directly at optic disc's front end
Early Views about Eye
- Pre 17th century: lens are structure for sensing coming of light
- Kepler: Brought forth evidence that it was retina, not lens that sensed light
using photoreceptors
- Schiener: lens was focusing device
Retinal Layers
- 3 main layers
[1] ganglion cell layer (frontal)
[2] bipolar cell layer (mid-region)
[3] photoreceptor layer (back, at deepest part of retina)
- Incoming light passes thro - [1] -- > [2] --> [3]
- Transparent cells above photoreceptors
Photoreceptor Response and Three-Cell Chain
- respond to light and pass info via transmission,
photoreceptor cell -> bipolar cell --> ganglion cell --> brain (via optic
nerve)
- \ bipolar cells: retinal neuron that picks up info from photoreceptors &
passes it to ganglion cells
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