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orbit
the bony opening in the skull that houses the eyeball
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blink
- rapid closing of eyelids
- corrlated with less activity in the prefrontal cortex
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sclera
- white outer covering of the eye
- helps the fuilid filled eyeball maintin its shape
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cornea
- the transparent outer layer of the eye
- bc it's curved, it begins the process of bending/refracting light rays to form an image in the back of eye
- clear, blood vessel-free extenseion of sclera (discouraged by proteins)
- greater density of pain receptors than nearly any other part of body
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anterior chamber/aqueous humor
area of eye located behind the cornea, contains AH
the fluid that gives the cornea its nutrients
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pupil
- the opening in the front of the eye controlled by iris
- diameter is affected by emotional state
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iris
- circular muscle in the front of eye that controls the opening of pupil
- color is influenced by amount of melanin pigment
- adjusts the opening of pupil in response to amount of light present in environment
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Lens
- directly behind IRIS
- helps focus the light on the retina in the back
- trasnparent due to fiber organization/lack of blood vessels
- depends on AQ
- muscles attached to lens allows us to accomodate
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Accomodation
the ability of lens to change shape to adjust to the distance of the visual stimulus
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Vitreous chamber/vitreous humor
- the major interior chamber of eye
- contains vitreous humor
- VH the same one you were born with
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Retina
- eleborate netowrk of photoreceptors and interneurons at the back of eye that is repsonsible for sensing light
- image that is projected on R is upside down and reversed relative to actual orientation of object viewed
- 3 layers of R
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Photoreceptors
- Specialized sensory cell in the retina that responds to light
- located in deepest layer of retina
- before light reaches PR it must pass through VH, blood vessels, and neural layers
- our visual system tunes out stimuli that remains constant (don't see vessels)
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Optic Nerve
fiber pathway that is formed by axons of ganglion cells as they leave the eye
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Optic disk
- area in retina where blood vessels and the optic nerve exit the eye
- does not contains any PR (blind spot)
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Macula
- a 6 mm round area in retina that is not covered by blood vessels and is specialized for detail version
- responsible for central vision, not peripheral vision
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Central vision
ability to perceive visual stimuli focused on the macula of the retina
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Peripheral vision
the ability to perceive visual stimuli that are off to the side while looking straight ahead
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Fovea
- center of macula, where the retina becomes thin and forms a pit (1.8mm)
- specialized for detailed vision and contains only one type of PR (cones: permit vision in bright lights, exlcusive to primates)
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Epithelium
- pigmented layer of cells that the retina is embedded in
- support the PR and absorb random light (why interior of eye looks black when seen thru pupil)
- camera flash: we see reflection of true red color of retina that results from rich blood supply, by reflecting light through eye a 2nd time, the odds of perceiving very dim lights at night are improved (white compound in nocturnal animals)
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Ganglion cell layer
- layer of retinal interneurons farthest from the PRs
- conains ganglion cells and gives rise to the optic nerve
- each GC has a single axon, which form the optic nerve as it leaves retina
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Inner plexiform layer
- dendrites of GCs form connections with the amacrine/bipolar cells OR
- contiains axons/dendrites that connect the ganglion, bipolar, and amacrine cells
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Amacrine cell
- retinal interneuron in the inner nuclear layer that integrates signals across adjacent segments of the retina
- forms connections with BPs, GCs, and other ACs
- processes movement
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Bipolar Cell
- cell in inner nuclear layer of the retina that forms part of the straight pathways between PRs and GCs
- receive input from PRs and HCs
- communicate with Amacrine and GCs
- produces graded potentials rather than action potentials
- idenitifes contrast with receptive field
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Inner Nuclear Layer
layer of retinal interneurons containing AMACRINE, BIPOLAR and HORIZONTAL cells
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Outer Plexiform Layer
retinal layer containing axons and dendrites forming form connections between BIPOLAR cells hnwith horizontal cells and PRs
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Horizontal cells
- retinal interneuron located in the inner nuclear lyaer that integrates signals from across the surface of the retina
- receive input from PRs and provide output to bipolar cell
- integrate info from PR that are close to one another
- communicates thru formation of graded potentials
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Outer Nuclear Area
in retina area that contains cell bodies of the PRs
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Rods/Scotopic vision
- a PR that responds to low levels of light but not to color
- SV: ability to see in dim light
- long cylinder shaped outer segment containing large # of disks (contains rhodopsin)
- no info on color, no sharp imges
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Outer segments
- portion of PR containing photopigemnts
- part of PR that absorbs light
- gives Cones and Rods the shape/name
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Photopigments
pigment contained in the PR of the eye that absorbs light
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Rhodopsin
- the photopigment found in rods
- allows rods to be 1000xs more sensitive to light than cones
- absorbs photons most effectively at wavelenths of 502 nm (blueish green)
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Cones/Photopic vision
- PR that operates in bright conditions and responds differentially to color
- 6 million cones in the eye
- PV: vision in bright light, sensitive to color and provides excellent clarity
- outersegment of cone is shorter and more pointed than rods
- stores 1 of 3 PHOTOPIGMENT in a folded membrance rather than in disks
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Transduction
process of translating a physical stimulus into electrical signals that can be understood/processed by the nervous system
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Opsin/Retinal
- Rhodopsin is made up of these 2 parts
- protein chain/ chemical made from vitamin A
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11-cis/all-trans
- when retinal is bound to opsin in abesnece of light
- form taken by retinal after ligth is absorbed by rod outer segment
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Dark Current
the steady depolarization maintained by PRs when no light is present
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cGMP
- 2nd messenger within PRs taht is responsible for maintaining the dark current by opening sodium channels
- when rhodopsin molcules break apart after light, enzymes that break down cGMP are released so fewer sodium channels stay open so it becomes hyperpolarized
- PRs release largest amounts of glutamate in the dark
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3 types of CONES
- blue/short WL: contains cyanolabe, 419 nm, violet
- green/middle WL: contains chlorolabe, 531 nm, green
- red/long WL: contains erythrolabe, 558 nm, yellow
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Receptive Field
location on retina at which light affects the activity of a particular visual interneuron
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Lateral Inhibition
- process in which active cells limit the activity of neighboring, less active cells
- PRs/HCs limit the activity
- produces sharpening/exaggeration of BPs responses to differences in light fallin on adjacent areas
- identifies boundaries/edge
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Ganglion Cells
- receives input from BP/ACs
- forms action potentials, not silent
- 1 million
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M cells
- large cells that respond to all WLs regardless of color, subtle differences in contrast and stimuli that come and go rapidly
- larger receptive fields
- provides info about large low contrast moving objects
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P Cells
- small and responds to high contrast and color
- responds to particular color
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K cells
- do not fit criterias for M and P cells
- respond to blue and yellow
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optic chiasm
area at base of brain where Optic nerves cross to from optic racts
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optic tracts
fiber pathways between OC and destinations in the forebrain and brainstem
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Superior colliculus
10% of axons in OT go to SC
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Lateral Geniculate Nucleus
- 90& of OT axons form synapses here
- 6 layers... first 2 are magnocellular layers: receive input from M cells
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Parvocellular laryers/Koniocellular layers
- 4 dorsal alyers of the LGN that receive input from P cells
- layers of small neurons between the larger 6 layers of LGN that receive input from K cells in ganglion layer
- 80% of input to LGN comes from striate cortex, braintem reticular formation
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primary visual cortex/striate crotex
occipital lobe for initial cortical analysis of visual input
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