Ch. 12: Retinal Physiology

Question 1

where is an extracellular recording taken and what does it measure?

Answer 1

placed in extremely close proximity to a neuron, records action potentials generated by the neuron

Question 2

where is the intracellular recording taken and what does it measure?

Answer 2

microelectrode pierces the neurons membrane and records the membrane potential

Question 3

what is a receptive field?

Answer 3

an area that influences neural activity

Question 4

what is spontaneous activity/ maintained discharge of a neuron?

Answer 4

action potentials which occur in the absence of a stimulus

Question 5

how is center-surround organization described?

Answer 5

light falling on the receptive fields center has the opposite effect of light falling on the surrounding area of the receptive field

Question 6

if light falls on the the receptive field surround, is the cell excited or inhibited? what happens to the action potential?

Answer 6

inhibits the cell and there is a reduction in action potential frequency

Question 7

is spatial grating a strong stimulus for a ganglion cell?

Answer 7

yes because of the contrast of the excitatory center and inhibitory surround

Question 8

why must intracellular recording techniques be used to measure the potentials of photoreceptors?

Answer 8

because photoreceptors only generate graded (slow) potentials not action potentials

Question 9

what are the 2 retinal cells that generate action potentials?

Answer 9

amacrine and ganglion cells

Question 10

what happens to a photoreceptor when it is exposed to light?

Answer 10

the potential goes from -50mV to a value closer to -70mV (hyperpolarize)

Question 11

in dark conditions (dark current), in which direction does Na+ flow (into or out) through the rod outersegment?

Answer 11

into the rod outersegment to allow depolarization, but as soon as light is flashed the Na+ pore is blocked leading to hyperpolarization

Question 12

what are the two portions of rhodopsin?

Answer 12

opsin and chromophore

Question 13

what does opsin determine?

Answer 13

the absorption profile of the photopigment

Question 14

what allows chromophore to be responsive to light?

Answer 14

retinal

Question 15

once light strikes an unbleached rod, what happens?

Answer 15

the 11-cis retinal is converted to 11-trans retinal, which initiates the hyperpolarization cascade in rods

Question 16

what are the classes of horizontal cells?

Answer 16

H1 and H2

Question 17

which horizontal cell receives primary input from M and L cones?

Answer 17

H1

Question 18

which horizontal cell receives strong connectivity from the S-cone?

Answer 18

H2

Question 19

what are the first retinal cells to display spatial antagonism?

Answer 19

bipolar cells

Question 20

how are on-center bipolar cells described?

Answer 20

invaginating synapse that they make with photoreceptors in the outer plexiform layer

Question 21

how are off-center bipolar cells characterized synaptically?

Answer 21

conventional flat synapse with photoreceptors

Question 22

how does a horizontal cell sum up input from large area of the retina?

Answer 22

high degree of spatial summation

Question 23

what do bipolar cells synapse with? and where do they synapse?

Answer 23

with ganglion cells in the inner plexiform layer

Question 24

what neurotransmitter is responsible for causing on-bipolar cells and off-bipolar cells in the outer plexiform layer?

Answer 24

glutamate

Question 25

how does glutamate affect an on-bipolar cell?

Answer 25

inhibitory, so when the on-bipolar cell is excited there is a reduction of glutamate on the bipolar cell

Question 26

under what conditions is neurotransmitter released?

Answer 26

dark conditions

Question 27

do diffuse bipolar cells have smaller soma and less extensive extensive dendritic trees?

Answer 27

no midget cells do

Question 28

how many M or L cones occupy the receptive field center of a midget cell in the central/midperipheral retina?

Answer 28

one

Question 29

which type of bipolar cell (midget or diffuse) is responsible for color opponency?

Answer 29

midget

Question 30

how many cones occupy the receptive field of a diffuse bipolar cell?

Answer 30

5-10

Question 31

what 2 things do midget cells manifest?

Answer 31

color opponency and high spatial resolution

Question 32

how do amacrine cells respond to stimulus?

Answer 32

briefly (transiently) at the stimulus onset and offset. makes them important in coding movement

Question 33

do amacrine cells express graded potentials?

Answer 33

no. action potentials

Question 34

what are midget ganglion cells referred to as?

Answer 34

parvo cells (70% of foveal and non foveal ganglion cells)

Question 35

what does an on-center diffuse bipolar cell synapse with?

Answer 35

on-center parasol ganglion cell

Question 36

what is another term for parasol ganglion cell?

Answer 36

magno cells

Question 37

what do S-cone bipolar cells synapse onto?

Answer 37

small bistratified cells

Question 38

in the fovea, how many midget bipolar cells synapse onto a midget ganglion cell?

Answer 38

one (limited spatial summation but they have high spatial resolution)

Question 39

do parasol ganglion cells have large dendritic trees and synapse with more than one diffuse bipolar cell?

Answer 39

yes

Question 40

what is the primary destination for an action potential fired from a ganglion cell?

Answer 40

LGN

Question 41

when do the axons of ganglion cells become myelinated?

Answer 41

as they leave the eye at the disc to form the optic nerve

Question 42

how do parasol ganglion cells respond to a flash of light?

Answer 42

transiently

Question 43

how do midget ganglion cells respond to a flash of light?

Answer 43

sustained response

Question 44

what leads to the formation of the konio pathway?

Answer 44

axons of the bistratified ganglion cells