Neu 330 Mod 3: ON/OFF pathways, receptive fields, and colors

convergence and ganglion cells

• each ganglion surveys different amount of photoreceptors

  • different amount of input

  • size determines amount of photoreceptors they receive

Which has larger receptive fields: rods and cones?

• rods

  • a lot of convergence onto ganglion cells

if we increase # of photoreceptors

• need larger receptive field

• lower usual resolution

Scotopic, mesotopic, photopic range graph

Rods

• more sensitive to light

• more rods

• low resolution

• peripheral

cones

• high resolution, center

• WIDER RANGE of activity

bleaching properties

• opsins stop working circumstantially

  • dark → sunny

    • bleach cones

  • sunny —> dark

    • bleach rods

horizontal cell function (center-surround)

• allows bipolar cell to be stimulated by surround photoreceptors

horizontal cells release

GABA

in dark are horizontal cells depolarized or hyperpolarized

depolarized

• AMPA receptors are going to be deactivated and let in sodium

depolarized HC

increase GABA → decrease glutamate

How do horizontal cells inhibit photoreceptors (on cells)

1. in darkness, glutamate released and triggers horizontal cell action

2. in darkness, hc release GABA to surround

   1. lateral inhibition

on bipolar respond to light in center

• in light, photoreceptor hyperpolarizes

• on-bipolar → depolarize

• on ganglion → depolarize

in darkness what do h-cells do

• make GABA

in darkness, what will h-cells do to on pathway of cells in surround

• GABA inhibits glutamate release

• depolarize

M Cells vs p cells

• m cells larger

• m cells

  • transient increase in AP but rapid decrease

• p cells

  • transient increase but prolonged

input and information for m cells vs. p cells

M Cells

• rods

  • movement

  • depth

  • subtle light diff

p cells

• Cones

  • color

  • fine details

L cones encode

red

M cones encode

green

S cones encode

blue

+L-M

• activated/excited by red L cones, inhibited by green M cones