Center Surround (M1)

Question 1

Where must a spot of light be shown on an OFF bipolar cell in order to get it to hyperpolarize?

Answer 1

center of its receptive field

Question 2

What happens when an annulus of light is shown on an OFF bipolar cell?

Answer 2

depolarize

Question 3

What is the idea that if both center an surround of a bipolar cell is stimulated at the same time then the resulting response is the sum of the two?

Answer 3

center-surround antagonism

Question 4

What is the center component in the center-surround antagonism due to? 1. What is the surround component due to? 2

Answer 4

1. direct input from photoreceptors

2. interaction between horizontal cells and either PRs or bipolars

Question 5

What neurotransmitters do horizontal cells use onto photoreceptors? 1. What channels do these open and where do the ions flow? 2. What is this process called? 3

Answer 5

1. GABA and glycine
2. chloride into the neuron (hyperpolarize)
3. lateral inhibition

Question 6

In the dark, if a PR is removed from its connection with horizontal cells would the PR be more depolarized or hyperpolarized?

Answer 6

depolarized

Question 7

What is the process when a neighboring photoreceptor is stimulated but not the one in question?

Answer 7

1. horizontal cell hyperpolarizes
2. LESS release of inhibitory compound (GABA) on PR in question
3. PR disinhibited and glutamate release increased
4. OFF bipolar further depolarizes
5. ON bipolar further hyperpolarize

Question 8

What does the center-surround antagonism provide for?

Answer 8

enhanced edge that separates highlights and shadows

Question 9

What does center-surround antagonism lead to in terms of our absolute sense of intensity?

Answer 9

makes it very poor

Question 10

What is the idea that apparent brightness of an object is inversely related to the luminance of its surroundings called?

Answer 10

simultaneous contrast

Question 11

What is the human visual system especially good at?

Answer 11

contrast detection

Question 12

What is the idea that objects have a similar appearance regardless if viewed under bright or dim lighting conditions called?

Answer 12

lightness constancy

Question 13

Where is the axon terminal of bipolar cells?

Answer 13

inner plexiform layer

Question 14

What is the neurotransmitter released by bipolar cells? 1. When is this releases (depolarized or hyperpolarized)? 2. What is the release dependent on? 3

Answer 14

1. glutamate
2. depolarized
3. Ca2+

Question 15

How many postsynaptic processes are along the active zone of a bipolar cell (and what are the cells in these positions)? 1. What is in the middle of these? 2. What is this arrangement called? 3

Answer 15

1. two (one amacrine and one ganglion cell)
2. ribbon
3. dyad synapse

Question 16

What kind of receptors are found on retinal ganglion cell dendrites?

Answer 16

1. AMPA/kinate-type glutamate receptors

2. NMDA-type glutamate receptors

Question 17

Is the synapse between bipolar cells and ganglion cells sign-conserving or sign-inverting?

Answer 17

sign-conserving

Question 18

Where are the dendrites of OFF RGC cells located? 1. ON RGC cells? 2

Answer 18

1. inner portion of IPL

2. outer portion of IPL

Question 19

Do retinal ganglion cells have graded potentials or action potentials when depolarized?

Answer 19

action potentials

Question 20

With increased depolarization, what happens to the retinal ganglion potentials?

Answer 20

increase in action potential spike frequency

Question 21

What do extracellular recordings of RGCs detect? 1. What can they be used to monitor? 2

Answer 21

1. detect action potentials

2. light-induced changes in spiking frequency

Question 22

What is the light-induced increase in activity of ON RGCs and ON-OFF RGCs primarily driven by? 1. In light, do the bipolar cells hyperpolarize or depolarize (and do they release more or less glutamate)? 2

Answer 22

1. ON bipolar cells

2. depolarize (more)

Question 23

What is the light-induced decrease in activity of OFF RGCs and ON-OFF RGCs primarily driven by? 1. In light, do the bipolar cells hyperpolarize or depolarize (and do they release more or less glutamate)? 2

Answer 23

1. OFF bipolar cells

2. hyperpolarize (less)

Question 24

What are the surround responses of RGCs driven by?

Answer 24

1. bipolar cells (mainly)

2. inhibitory input from amacrines