COGS 17 Lecture Notes - Lecture 6: Retinal Pigment Epithelium, Ganglion Cell, Pigment
19 May 2018
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Lec 4A - Vision
● The eye
○ Structure of the eye
○ Fovea → point of central focus
● The retina
○ Receptor cells - farthest back of all the cells. Outer segments of
receptors respond to light
○ Mostly bipolar cells
○ Ganglion cells
○ Axons from ganglion cells
● Comparing rods and cones → on class website
○ Visual receptors: rods and cones
■ Cone-shaped outer-segment, layered with photo pigment
■ Cell body
■ Rod’s outer segment much larger than cone’s
■ Rods, being larger have more photo pigment
○ Distribution of rods and cones across retina
■ Cones
■ Rods
● Visual receptors: rods and cones
○ Similarities
■ Molecules of photopigment embedded in outer segments
■ Outer segments embedded in “pigment epithelium”
■ Graded potentials
■ Release inhibitory neurotransmitters
○ Differences
■ Cones
● 3 kinds of photopigment (1 type per cone)
● codes colour
● poor for motion detection
● excellent acuity (detail discrimination)
● low sensitivity (require bright light)
● mainly ventral path (v1)
■ Rods
● 1 kind of photopigment
● do not process/code colour
● excellent for motion detection
● poor acuity
● high sensitivity (operate in dim light)
○ Active in the dark, turned off by light
■ Outer segment with molecules of photopigment (visual purple)
■ Typical distribution of ions in inactive cell: K+ concentration
inside, Na+ and Ca++ outside
■ Ion channels
■ The “dark current”
find more resources at oneclass.com
find more resources at oneclass.com
Document Summary
Receptor cells - farthest back of all the cells. Comparing rods and cones on class website. Rod"s outer segment much larger than cone"s. Rods, being larger have more photo pigment. Distribution of rods and cones across retina. Molecules of photopigment embedded in outer segments. 3 kinds of photopigment (1 type per cone) Mainly ventral path (v1) low sensitivity (require bright light) Active in the dark, turned off by light. Outer segment with molecules of photopigment (visual purple) Typical distribution of ions in inactive cell: k+ concentration inside, na+ and ca++ outside. As na+ accumulates in cell, na+ in, the change in polarity opens ca++ gate, ca++ enters, ca++ in, neurotransmitters release. As positive charges accumulate in cell, na+ exits, via electrostatic pressure. Ejection of ca++ should end nt release, but whole cycle starts again. Nt is repeatedly released as long as there is no.
