Download What happens in hereditary color deficiency? Red or green cone

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sensory transduction
◦ - conversion of physical energy from the
environment into changes in electrical potential
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sensory coding◦ Making sense of that input
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vision - light waves -
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taste – chemicals in fluid –
hearing – sound wavestouch- pressure, temperature changes,
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smell- chemical in air
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vision
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taste hearing -
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touch
smell
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Receptors show adaptation
◦ most sensitive to changes rather than constant
stimulation
◦ why is this important?
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General pathway for most sensory
information:
◦ sensory neurons – sensory nerves
 spinal tracts –
 thalamus –
 primary cortex –
 higher association cortex
Certain sensory neurons have a
spontaneous firing rate.
For these cells any change in their firing
rate will convey important info (i.e. color
vision)
Different rhythms of firing also can convey
different information
* most highly developed sense in humans
optic nerve for one eye - 1,000,000 axons
auditory nerve contains about 30,000
axons
adaptability and plasticity of visual system
- make sense out of nonsense
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iris
◦ largely a muscle that expands and contracts pupil
in response to light
◦ phenotypically unique –
 iris scan
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sclera
◦ tough opaque tissue
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pupil
◦ often used to determine neurological function
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light waves along the visual spectrum
1.
2.
inverted image on retina
region important for transduction is at very
back of the eye
retina - structure of eye important for
transduction
- retina contains neurons, glial cells and two
types of photoreceptors
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responsible for transduction
numerous differences between rods and
cones
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rods
shaped like a rod
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cones
shaped like a cone
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a low ratio of synaptic connections between
neurons ensures higher definition and
sharpness compared to a higher ratio
less sharp focused
visual input
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rods
shaped like a rod
insensitive to color
work well under low
illumination
20,000,000/eye
location: found around the
periphery of the retina
requires extended time until
optimal function
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cones
shaped like a cone
sensitive to color
work best in bright light
5,000,000/eye
location – found around
the fovea of the retina
responsible for sharp
images and vision
works optimally very
quickly
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there are at least two levels of communication
within the neural cells of the eye
◦ rods and cones – bipolar cells – ganglion cells
(axons make up the optic nerve) to CNS
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there are at least two levels of communication
within the neural cells of the eye
◦ rods and cones – bipolar cells – ganglion cells
(axons make up the optic nerve) to CNS
◦ across a single layer (rods and cones communicate
with each other; bipolar cells communicate with
each other; etc)
optic nerve (ganglion cell axons) – make a
blind spot on each eye!
8 inches
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component (trichromatic ) or YoungHelmholz
◦ occurs at level of cones
 3 different cones more sensitive to different
wavelengths (ie colors)
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trichromatic or Young-Helmholz
◦ occurs at level of cones
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explains major type of color blindness
◦ deficits in certain types of cones can explain major
type of color blindness
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At level of cones- GREAT!
◦ there are different cones that produce greater changes in
electrical potentials depending on the color (wave)
◦ abnormalities in cones can explain red/green color
blindness
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Very rare to see complete color blindness - only
usually seen with brain injury
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~ 7% of US males (10,000,000) compared to 0.4%
women - red/green
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X-linked phenomenon
X
X
b
X
Y
XX
XY
XX
b
b
X Y
What happens in hereditary
color deficiency?
 Red or green cone peak sensitivity is shifted.
 Red or green cones absent.
35
437 nm
B
533 nm
564 nm
G
R
36
5% of
Males
437 nm
B
564 nm
G
R
(green shifted toward red)
37
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At level of cones- GREAT!
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negative afterimage –
◦ phenomenon that occurs as a result of overactivity
or inhibition of neurons (due to color stimulation)
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opponent process theory
◦ occurs at level of bipolar cells and higher
 black/white, red/green; yellow/blue; one color excites
bipolar cell; other color inhibits it
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says nothing about complexity as information
reaches occipital lobe –
prestriate – primary occipital cortex; multiple
layers of higher association cortex
Copyright © 2006 by Allyn and
Bacon