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9.2 VS functional Anatomy (9.2.3 Types of retinal neurons (cone (bipolar…
9.2 VS functional Anatomy
9.2.1 Structure of the retina
Light through the pupil into the eye
light interacts with light-sensitive retina
photoreceptor cells are stimulated
construction of visual world begins
and neurons have multiple functions
convert light into action potential
allow discrimmination between colors
allow discrimmination between light intensities
image projected onto retina is upside down and backwards
Center of the retina is the fovea, there the image is sharpest
Blind spot on the retina has no photoreceptor, therefore no conversion of light, thus no vision
9.2.2 Photoreceptors
light interacts with the photoreceptors
changed into chemical energy
changed into neural activity
eventually leads to a difference in release of neurotransmitters
Two types of photoreceptors
rods
very sensitive to dim light/low levels of brightness
function for night vision
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cones
sensitive to bright light
function for color vision and fine detail
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fovea only has cones
rest of the retina, the cones are much less dense
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9.2.3 Types of retinal neurons
cone
bipolar cells
cone
horizontal cells
thy bridge between the cones and give signal to the bipolar cells
determine how much signal from the receptor goes to the RGC
activated by color
rod
bipolar cells
retinal ganglion cells
the only output of the eye
axons meeat and leave through optic nerve
optic nerve is also the blind spot
Parvocellular cells (P-cells)
sensitive to color, but not light
most information through cones
found in the fovea
Magnocellular cells (M-cells)
sensitive to light, but not color
most information through rods
found in the retina
connect the receptors to the ganglion cells
activated by black and white
9.2.4 Visual Pathways
many RGCs are photosensitive, aka pRGCs
play a role in circadian rythms and expansion/contraction of pupil in response to light
act as photoreceptors
partly form the RETINOHYPOTHALAMIC TRACT
RGC axons seperate whhen they enter the brain
remaining M axons form a pathway
TECTOPULVINAR SYSTEM
starts in the eye
through midbrain tectum to the pulvinar
function is to bypass the occipital visual regions and send connections to parietal and temporal
all P axons and some M axons form a pathway
GENICULOSTRIATE SYSTEM
Both systems end in either temporal or parietal lobe
to temporal lobe is dorsal stream
AKA the how stream as it controls movements to or from the stimulus
to parietal lobe is called ventral stream
AKA what stream as it identifies a stimulus
Starts in the retina
crosses the lateral geniculate nucleus in the thalamus
travels to layer IV of the primary visual cortex in occipital lobe
forms a bride between thalamus and striate cortex
one route to temporal lobe
one route to parietal lobe