Lecture 7

Question 1

Photoreceptor signalling

Answer 1

Signal to bipolar cells via glutamate + photon decreases glutamate release

Question 2

OFF bipolar cells

Answer 2

• Dimming
• Ionotropic glutamate receptors
• Depolarized in the dark
• Upper inner plexiform layer (IPL)
• Connect to OFF ganglion cells, short
• AMPA & kainate receptors
• photoreceptor –(excitatory glutamate)→ OFF bp —(EG)→ OFF rgcs

Question 3

Where are bipolar cell bodies & axon terminals?

Answer 3

Bodies: inner nuclear layer
Axon terminal: inner plexiform layer

Question 4

ON bipolar cells

Answer 4

• Brightening
• Metabotropic
• Depolarized in light, hyperpolarized in dark
• Deeper IPL
• ON ganglion cells, longer
• mGIuRG receptors
• PR –(inhibitory glu.)→ ON bp –(EG)→ ON RGC

Question 5

AP frequency in RGCs

Answer 5

Corresponds to intensity
Related to the difference in stimulus/background
Proportional over ~ 2log units
ADAPTS, NEW BASELINE

Question 6

Receptive field firing rates

Answer 6

(see 7.11)

Question 6

Retinal path inside vs outside fovea

Answer 6

INSIDE fovea: cone = center of ON & OFF path

OUTSIDE fovea: more photoreceptors → single RGC

(see 7.6)

Question 6

Daytime vs nighttime circuits

Answer 6

DAYTIME: cone circuit, synapse directly w/ RGC

NIGHTTIME:cone + rod circuit!
Rods → own ON bipolar cell → glutaminergic synapses w/ all amacrine cells → gap junction (electrical) w/ on come bipolar cells → RGC
*RODS DO NOT generally wake direct synapses

Question 7

Tiling

Answer 7

Ganglion cells specific to visual features ‘tile’ retina:

a b c a b c a b c
d e d e d e

        a b c                  a b c
         d e                     d e

Question 7

ON & OFF receptive fields

Answer 7

ON-center:
excited by light in center
inhibited by light in periphery

OFF-center:
inhibited in center (field)
excited in periphery (surround)

Good for edge detection

Question 8

Horizontal cells

Answer 8

Negative feedback to photoreceptors
Hyperp. photoreceptor → hyperp. horizontal cell → slightly depolarized photoreceptor

Only center: depolarization too slight to matter
Center + surround: depolarization → less AP in RGCs

Question 9

Luminance vs. brightness

Answer 9

Luminance: physical measurement of light intensity

Brightness: sensation from light intensity

Good @ brightness, bad at luminance

Question 10

Direction sensitive cells

Answer 10

starburst amacrine cells inhibits dsRGCs
Preferred direction excites dsRGCs before amacrine
Null: amacrine cells inhibit before dsRGC excitation

• Required for optokinetic reflex

Question 10

Color example

Answer 10

Red ON + green OFF
maximizes red light response
minimizes green light reponse