PSYCH 454 Lecture Notes - Lecture 9: Visual Acuity, Rhodopsin, Retina
24 May 2018
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Lecture 9: Eye- Photoreceptors (2)
Photoreceptors
● Different pigments contain different proteins called “opsins” giving rise to differences in
color sensitivity
● 2 types of photoreceptors: each contain light sensitive photopigment
○ Rods → all have same photopigment “rhodopsin”
■ Larger of the two
○ Cones → 1 of 3 types of photopigments (short
medium or long)
● Rods/Cones similarities
○ Outer segments: contain photopigment in disc like
structures, inside cones too
○ Inner segments: cell bodies, nucleus
○ Synaptic terminals- make connection with next
chain of cells
● Rods/Cones Differences
○ Shape of outer segment
■ Rods have rod like outer segment
■ cone= conical type
● Rods and cones differ in light sensitivity
○ rods= sensitive to dim light → useful for
dark/nighttime
○ cones= need much brighter light → useful for
daytime
■ Higher acuity vision
Different across the Retina
● Highest density of cones at fovea
○ Fewest cones in retinal periphery (further away from fovea)
○ # of cones decreases as you move away from the fovea
● Rods = more numerous retinal periphery
○ Few (no) rods in fovea (most sensitive part of eye)\
● Also NO rods @ optic disk
● Rod pathway
○ # of rods provides converging input to bipolar cells
○ This arrangement amplifies the visual input to ganglion cells under low light
conditions
(but reduces visual acuity)
○ Multiple bipolar cells provide input to a single ganglion cell
○ Find this in peripheral retinal because thats where rods are
● Cone Pathway → day
○ Cones in fovea may provide one to one input to bipolar cells
Document Summary
Different pigments contain different proteins called opsins giving rise to differences in. 2 types of photoreceptors: each contain light sensitive photopigment color sensitivity. Rods all have same photopigment rhodopsin . Cones 1 of 3 types of photopigments (short. Outer segments: contain photopigment in disc like structures, inside cones too. Synaptic terminals- make connection with next chain of cells. Rods and cones differ in light sensitivity. Rods= sensitive to dim light useful for dark/nighttime. Cones= need much brighter light useful for daytime. Fewest cones in retinal periphery (further away from fovea) # of cones decreases as you move away from the fovea. Few (no) rods in fovea (most sensitive part of eye)\ # of rods provides converging input to bipolar cells. This arrangement amplifies the visual input to ganglion cells under low light. Multiple bipolar cells provide input to a single ganglion cell. Find this in peripheral retinal because thats where rods are conditions (but reduces visual acuity)
