Vision

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28 Terms

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Cornea

Outer cover where light first passes through

  • helps focus light rays
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Pupil

Small adjustable opening in the iris

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Iris

muscles that dilate/restrict pupil

  • responds to light intensity or emotions
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Lens

focuses light into an image projected onto retina

  • image is reversed (but is later unreversed in the brain)
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Retina

  • the light-sensitive inner surface of eye
  • 3 layers of nerve cells (photoreceptors, interneurons, afferent cells)
  • transduces light into neural signals
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Fovea

Tiny pit filled with cones

  • responsible for sharp vision
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Optic Nerve

thick rope of intertwined ganglion axons

  • carries messages to brain
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Blind Spot

area without visual receptors because it's where blood vessels and nerves connect to eyeball

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1) Photoreceptor Cells

  • First layer of retina
  • rods and cones
  • transduces light (distal stimulus) into neural signal (proximal stimulus)
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Rods

  • a type of photoreceptor cell
  • detect black and white
  • peripheral vision
  • dim light (nighttime)
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Rods

What kind of photoreceptor cell works best at night?

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Rods

what kind of photoreceptor cell is responsible for peripheral vision?

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Cones

  • a type of photoreceptor cell
  • sensitive to red, green, or blue
  • works best in daytime
  • detailed vision
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Cones

What kind of photoreceptor cells work best at daytime/in bright light?

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Cones

What kind of photoreceptor cells are responsible for detailed vision?

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2) Bipolar Cells

  • Second layer of retina
  • specialized interneurons
  • connect photorecptors to ganglion cells
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3) Ganglion Cells

  • third layer of retina
  • specialized afferent neurons
  • have long axons that intertwine
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Visual Cortex in Occipital Lobe

Final Destination of visual neural message?

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Trichromatic Theory

“there are only 3 types of photoreceptors, so we can only see red, green, and blue”

BUT

“when combined, these photoreceptors allow us to see ALL colors of light”

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Opponent-Process Theory

“2 sets of firing neurons that work in opposite ways”

ex. see blue → blue cones fire → neurons connected to those blue cones fire (excitatory messages) while orange gets suppressed (inhibitory messages)

evidence: afterimage (seeing opposite colors after staring at a color for awhile)

when excitatory signal disappears, the inhibitory briefly overshoots (out of balance)

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Light Adaptation

adjusting to brighter light

  • squinting and our pupils constricting
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Dark Adaptation

adjusting to dimmer light

  • pupils dilate quickly
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Near-sightedness

people can only see what’s near their eyes

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Far-sightedness

distant objects are clearer and near objects are blurry

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Cataracts

cloudy lenses

  • easily removed with surgery
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Glaucoma

excess fluid in eye presses on optical nerve so it can’t fire

  • pressure
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Color blindness

  • usually in males
  • red-green
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blindness

can be result of damage to eye, neurons, or visual cortex