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36 Cards in this Set

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General Structure of Rods and Cones

"pigmented base" of retina
outer segment (pigmented discs)
connecting stalk
inner segment (mitochondria)
outer fiber
cell body (nucleus)
inner fiber
synaptic ending
General Structure of Rods and Cones

"neural layer"
bipolar cell

ganglion cell (axons carried to brain by optic nerve)
outer segment
contain membrane-bound discs with pigments that absorb and react to light
rods
pigment discs stacked like pennies all the way to the base, membranes are DISTINCT from the plasma membrane
1. sensitive to dim light (night vision)
2. respond to ALL wavelengths (colors)
3. only "grey" information to the brain
4. 100 rods per ganglion cell to brain
5. widely spread throughout the retina
6. not good for visual acuity
rods
cones
pigment discs taper off toward the base, membranes are CONTINUOUS with the plasma membrane
1. require bright light for stimulation
2. different cones have different pigments specific for certain wavelengths (colors)
3. can convey color information to brain
4. 1-3 cones per ganglion cell to brain
5. primarily concentrated in fovea (center)
6. essential for visual acuity
cones
opsin
transmembrane protein in the membrane of pigmented discs of rods and cones
retinal
light absorbing molecule that changes shape when struck by a photon of light
precursor to retinal (eat your carrots!!!!!!)
vitamin A
non-activated form of retinal, prior to absorption of photon energy; has a "kinked" double bond
11-cis isomer of retinal
activated form of retinal, after struck by photon of light; double bond straightens out
all trans isomer of retinal
visual pigment in rods; in membranes of pigmented discs of outer segment
rhodopsin
breakdown of rhodopsin after the absorption of light
bleaching of pigment

11-cis retinal + scotopsin ~
rhodopsin + light ~ all-trans retinal + scotopsin
causes HYPERPOLARIZATION of rod
all-trans retinal
all-trans retinal
a. Na+ channels (open in dark) are closed
b. rod is hyperpolarized (increased negativity)
c. Ca++ channels in synapse close
d. less neurotransmitter released by the rod
3 distinct pigments in cones are sensitive to 3 different parts of visible spectrum
photopsins
maximum sensitivity at 455 nm
blue cones
maximum sensitivity at 530 nm
green cones
maximum sensitivity at 625 nm
red cones
differential activation of each of the three different cones
different colors
inherit gene for one of the photon proteins that is deficient (mainly male), most common are red and green mutations
color blindness
a. rhodopsin in rods is quickly bleached out
b. sensitivity to shallow light disappears
c. rods are inhibited by other retinal cells
d. cones are activated to take over (5 mins.)
e. consensual pupil reflex - constriction
Light and Dark Adaptation of Rhodopsin

1. light adaptation - very dark ~ very bright
a. cones are gradually cease to be stimulated
b. "bleached out" rods can produce rhodopsin
c. rods eventually take over in the dim light
d. pupillary dilation - pupils increase size
dark adaptation - very bright ~ very dark
deficiency in function of rods during dim-light situations
nyctalopia (night blindness)
nyctalopia (night blindness) - deficiency in function of rods during dim-light situations

general cause
vitamin A deficiency
The Visual Pathway: Photoreceptors to Occipital Cortex

photoreceptors (rods & cones) ->
bipolar cells ->
ganglion cells (axons = optic nerve) ->
RETINA path
The Visual Pathway: Photoreceptors to Occipital Cortex

optic nerves (from each eye retina)->
optic chiasma (medial fibers X over)->
optic tracts (opposite visual field)->
AXON PATH
The Visual Pathway: Photoreceptors to Occipital Cortex

lateral geniculate body of thalamus ->
THALAMUS
The Visual Pathway: Photoreceptors to Occipital Cortex

optic radiation (fibers to cortex)
AXON PATH
The Visual Pathway: Photoreceptors to Occipital Cortex

occipital lobe - primary visual cortex
CEREBRAL CORTEX
other brain areas that receive visual information:

for control of extrinsic eye muscles
superior colliculi
other brain areas that receive visual information:

mediate pupillary light reflexes
pretectal nuclei
other brain areas that receive visual information:

circadian rhythm
suprachiasmatic nucleus of hypothalamus
two eyes have overlapping regions of the visual field, so that the same point is seen from slightly different angles
binocular vision
a result of binocular vision in which person can perceive relative distances based on information gathered in both eyes
depth perception