Download Vision

Vision
Eyes, Optic Nerves, Ganglion
Cells, Occipital Lobe… Its got it
all!
I CAN
• Explain the sensation process as it applies
to sight using the anatomically correct
terms
Anatomy
Key Elements: Pupil, Lens, Retina, Fovea,
Photoreceptors- Rods and Cones, Optic
Nerve, Occipital Lobe
Visual Transduction
• Begins when light waves enter the eye
• Photoreceptors (rods and cones) on the retina
interpret the waves
– Rods work in the dark and are found all over the
retina (nearly 18X more rods than cones)
– Cones measure color and are found only on the
fovea (area of most focus on the retina)
• Bipolar cells take info from rods and cones to
the GANGLION CELLS (sense/afferent
neurons)
– GC AXONS ARE the Optic Nerve.
– So… TRANSDUCTION occurs in the retina.!
Brightness Explained
• How much light reaches the retina?
–Controlled by the PUPIL
• Dilated Pupil=DARK
• Contracted Pupil=LIGHT
–Pupil Dilates in the Dark to expose
more light waves to the
photoreceptors
»Many drugs can interfere with this by acting
as agonists (replicating the
neurotransmitters) involved in determining
Pupil dilation and Contraction! (Primarily
Dopamine and Endorphin)
How does the Visual System
Create Color?
• Color does not exist in the world, only in
the mind---WHOA!
– color is a sensation created when light waves
are transduced (I have no idea if this is the
correct past tense of transduction) and then
processed in our visual cortex
–Only CONES (visual receptor cells) can
detect color. These are only found in
the FOVEA
The Nature of Light
• Electromagnetic spectrum- range of
electromagnetic energy
– Visible spectrum- part of the electromagnetic
field that our brain can interpret in color
• To interpret energy outside of the visible
spectrum, we employ devices- radio’s,
TVs, etc
–Long waves- red
–Medium waves- yellows/greens
–Short waves- blues
Electromagnetic Spectrum
2 Theories for How we Sense
Colors
1. Trichomatic Theory: explains the initial stages
of color vision- 3 types of cones sense the
visible light- red, green, and blue
2. Opponent-Process Theory: explains vision
from the bipolar cells on- upon the sensation
of 1 color, your brain will inhibit its
compliment- red/green; yellow/blue, etc
• This explains the negative afterimage on p
121
Color Blindness
• Color weakness- shades and pale
colors are difficult to distinguish
• Color blindness- cannot see specific
colors
–Most red/green
–Rarely blue/yellow
–Only 500 ever have reported
complete color blindness
CAN I?
• Explain the sensation process as it applies
to sight using the anatomically correct
terms