Sfs - Early Visual Processing

Front 1

Type of contast in which the light from the object is brighter than the surroundings.

Back 1

positive

Front 2

Type of contast in which the light from the object is dimmer than the surroundings.

Back 2

negative

Front 3

Above threshold, the retina is less concerned with the number of photons and more interested in what?

Back 3

The contrast between two objects

Front 4

Is the inner or outer layer:
1. Closest to the vitreous humor?
2. Clostest to sclera; photoreceptors are here

Back 4

1. inner
2. outer

Front 5

Photoreceptors synapse on what type of cells and where?

Back 5

bipolar cells in the outer plexiform layer

Front 6

Bipolar cells synpase on what?

Back 6

Ganglion cells

Front 7

Photoreceptors in retina.

Back 7

Rods and cones. Allows for expansion of the visual range of the perception of light.

Front 8

Ganglion cells typically synapse where?

Back 8

Lateral geniculate nucleus

Front 9

Circuit involving horizontal and amacrine cells allowing lateral inhibition and center-surround organization.

Back 9

Lateral circuit; important for sensing contrast (color and light/dark)

Front 10

Important in determining light intensity increases and decreases.

Back 10

On/Off pathways

Front 11

Visual pigment in rods

Back 11

rhodopsin

Front 12

Visual pigment in cones

Back 12

photopsin

Front 13

Photoreceptors ___________ in the light and ____________ in the dark.

Back 13

hyperpolarize; depolarize

Front 14

Area of retina with a high density of cones and allows viewing of fine detail. Damage here can be detrimental to vision

Back 14

fovea

Front 15

95% of photoreceptors in humans.

Back 15

rods

Front 16

Photoreceptors requiring only one photon to fire. High degree of spatial summation. Very sensitive with poor spatial localization.

Back 16

Rods

Front 17

What kind of photoreceptors have slow temporal resolution?

Back 17

Rods

Front 18

Photoreceptors with high temporal resolution but less sensitivity. Wide range of adaptation due to circuit and internal photoreceptor adaptation. Color vision.

Back 18

Cones

Front 19

Difference in rod and cone function is due to what?

Back 19

Differences in the signaling cascades.

Front 20

Rod signaling cascade pathway.

Back 20

11-cis-retinal (light>conf. change) -> activates rhodopsin (GPCR) -> activates g-protein transducin -> activates phosphodiesterase which degrades cGMP.

Front 21

What modulates the membrane potential?

Back 21

Concentration of cGMP. Cleavage of cGMP causes membrane channel to close preventing ions from entering and depolarizing.

Front 22

1. Activates transducin 500 fold. High sensitivity, slow recovery.
2. Activates transducin 50 fold. Faster recovery. Less sensitivity.

Back 22

1. Rhodopsin
2. Opsin

Front 23

Increasing the brightness beyond the threshold does what to channels?

Back 23

Prevents the channels from reopening for longer.

Front 24

Photoreceptors fire what type of responses?

Back 24

Graded and continuous, not spikes

Front 25

NT of photoreceptors released in the dark.

Back 25

Glutamate

Front 26

Photoreceptors that generate a faster response, but require more photons.

Back 26

Cones

Front 27

What location in the eye does each photoreceptor have its own bipolar cell and ganglion cell?

Back 27

Fovea

Front 28

1. Wiring pattern increasing SENSITIVITY.
2. Wiring pattern increasing CONTRAST.

Back 28

1. Convergent (several photorecptors to one photoreceptor). Low spatial res, but sensitive.
2. divergent. One photoreceptor to more than one bipolar cell. On/off pathways.

Front 29

Push-Pull system

Back 29

Depolarization will stimulate one ganglion cell, while hyperpolarization will stimulate another. Generates larger signal differential to maximize contrast.

Front 30

________ pathways formed by horizontal and amacrine cells. ______ inhibition important in determining edges of an object.

Back 30

Lateral; lateral. Active photoreceptor inhibits its neighbors for sharp border between activation/inactivation.

Front 31

On/off pathways require ______ wiring. Response is determined by ________.

Back 31

Divergent; receptor type (not the NT)

Front 32

Has an inverting synapse. A secondary transmitter actually closes channels (hyperpolarization). Bipolar cell in other pathway has receptor that responds by opening channels.

Back 32

ON cell.

Front 33

The only photorecptor in the fovea that the bipolar cell receives input from.

Back 33

Midget bipolar cells (small dendritic arbor)

Front 34

Off pathway.

Back 34

Light hyperpolarizes > less glutamate released > off bipolar cell hyperpol. since no longer stimulated by NT > ganglion cell hyperpolarizes decreasing spike frequency

Front 35

On pathway.

Back 35

Remember inverting synapse. Dark; photoreceptor depol., so releases glutamine causing hyperpol in bipolar cell > ganglion cell hyperpolarized - spike freq. decreases. When light hyperpolarizes photoreceptor, ceases to release NT > channels in bipolar cell open, depolarizes > stimulates ganglion cell increasing spike frequency.

Front 36

Requires amacrine and horizontal cells to mediate lateral inhibition.

Back 36

Center and surround organization.

Front 37

Response from light stimulation.

Back 37

Transient.

Front 38

Has an inverted synapse and feeds back to ganglion cell to cancel out stimulus from bipolar cell.

Back 38

Amacrine cell (bipolar cell stimulates ganglion cell and amacrine cell)

Front 39

Fields that involve a midget ganglion cell receiving a signal from one central bipolar cell.

Back 39

Center and surround receptive fields

Front 40

Bipolar cells around the central bipolar cell in 3D space stimulate ________ cells feeding onto the ganglion cell in a(n) ________ fashion.

Back 40

amacrine; inverted

Front 41

If bipolar cells around central bipolar cell are also stimulated by light, the signal to the ganglion would actually _________.

Back 41

Decrease

Front 42

In the fovea, ganglion cells are highly __________.

Back 42

dispersed (from fovea photoreceptors)

Front 43

Determines if cell is an On or Off bipolar cell.

Back 43

Where the bipolar cell dendrite resides in the sublamina

Front 44

On responses are in the __________ ring.
Off are in the __________ ring.

Back 44

outermost; innermost

Front 45

Identified by their small dendritic arbors.

Back 45

Midget ganglion cells

Front 46

Responds when blue light goes on or yellow light goes off.

Back 46

Bistratified ganglion cell.

Front 47

Do not have specific ganglions, but piggyback signals through the cone system using AII amacrine cells.

Back 47

Rods

Front 48

Lighting conditions when rods and cones are both active

Back 48

mesoptic

Front 49

Pathway of rod stimulation.

Back 49

Rod photoreceptor stimulates rod bipolar cell which transfers signal to A2 amacrine cell, stimulating the cone system.
Rod system has a high degree of spatial summation.

Front 50

Encode brightness of light by temporal frequency.

Back 50

Spikes

Front 51

Leads to centersurround receptive fields by lateral inhibition.

Back 51

Contrast