BIO448-Vision II

rods

higher density of ___ in retina except in the fovea

reasons visual acuity/resolution is better in fovea

• high density of cones

• 1:1 relationship of cones to bipolar cell

• avascular zones, which leads to less optical distortion

color vision

___ is due to higher order processing within the visual system

color blind

cones are ___ they absorb photons at all wavelengths, even though they are more sensitive to a specific one.

hyperpolarization

A large number of photons is needed at wavelengths further from ideal one to get the same ___ as few photons do at ideal wavelength.

further from ideal wavelength = more efforts/more work required for same response

RGC

retinal ganglion cells

output cells of the retina

axons carrying output to the brain through optic nerve

2 types of cells behaviors

• one fires more when the central region on retina is illuminated. then goes back to spontaneous activity

• the other is inhibited from firing when central region of retina is illuminated, but fires more after illumination period

on center

increases discharge rate to luminance increases

off center

increase discharge rate to luminance decreases

2

each cone photoreceptor synapses on ___ different bipolar cells and each of these synapses on their respective ganglion cell

ON bipolar cell

• receive GLU from cone

• GLU binds to metabotropic/G-protein receptor mGluR6

• ___ depolarizes

• releases GLU onto respective ganglion cells

OFF bipolar cell

• GLU released from cone

• GLU bonds to AMPA and kainate receptor (both ionotropic)

• ___ hyperpolarizes

decreased luminance in OFF center cells

• cone releases GLU

• GLU binds to AMPA

• depolarization of bipolar cell

• more GLU released from bipolar cell

• depolarization of associated ganglion cell which increases activity

increased luminance in OFF center cells

• cone releases less GLU

• less GLU means less binding and less depolarization which causes a hyperpolarization of bipolar cell

• less GLU released from bipolar cell which inhibits activity

mGluR6

metabotropic glutamate receptor

activate second messenger when bound to GLU which closes cGMP-gated Na+ channels