Photoreceptor Bipolar Connections

Question 1

Horizontal cells in the OPL form synapses with __ and __ and communicate with ___.

Answer 1

They form synapses with rods and cones and communicate with bipolar cells.

Question 2

The rod spherule has ___ invagination with ____ synaptic ribbons with invaginating contacts.

Answer 2

One invagination with 1-2 ribbons.

Question 3

The cone pedicle has ___ synaptic ribbons with invalidating contacts. Each invagination contains __ horizontal cell processes and ___ or more bipolar cell processes.

Answer 3

many synaptic ribbons. 20 in fovea, 50 in periphery.
Each invagination contains 2 horizontal cell processes (each for different Horizontal cells) and 2 or more bipolar cell processes.

On the sides of the pedicle, there are flat contacts for flat midget bipolar cells. These are for synaptic transmission with bipolar cells. No ribbon here.

Question 4

Synaptic ribbons do what

Answer 4

Are organelles for NT release. Are able to elicit a graded depolarization when a high rate of SUSTAINED release of NT(glutamate) is required. Unsure how ribbons do this.

Question 5

What can bind to the single invagination of rod spherules?

Answer 5

2 Horizontal cell processes (different H cells) can bind on the right and left side.
In the center, there are processes from two or more rod bipolar cells.
No flat contacts.

Question 6

Which cells transmit visual info by graded potentials?

Answer 6

Photoreceptors, horizontal cells, bipolar cells and (most likely) amacrine cells

Question 7

Two types of graded potentials

Answer 7

While light is on- hyperpolarizing. Response change in the negative direction is considered inhibitory.
While light is on- Depolarizing. Response change in the positive direction is considered excitatory.

Information sent by varying the size/strength of the signal.

Question 8

Excitation vs inhibition of light

Answer 8

Excitation- the onset, or increase of light

Inhibition- The offset, or decrease of light

Question 9

Light on in the photoreceptor causes it to ____

Light off in the photoreceptor causes it to ___

Answer 9

Hyperpolarize 
Depolarize (relatively. The value does not become positive, but less negative)

Question 10

Light on in the horizontal cell causes it to ____

Light off in the horizontal cell causes it to ___

Answer 10

Hyperpolarize

Depolarize

Question 11

Receptive fields of horizontal cells vs photoreceptor filds

Answer 11

Horizontal cell has a larger receptive field. This is the area on the retina onto which presentation or removal of light will elicit a change in the response of that neuron.

Question 12

After photoreceptor cells are stimulated with light, they will hyperpolarize and stimulate Horizontal cells. How do horizontal cells respond?

Answer 12

The H cell responds to the light with the same change in polarity as the photoreceptors feeding it. Sign Conserving synapse. The H cell will hyper polarize since the PR did.

The H cells hyper polarization FEEDS BACK onto to cones, resulting in a depolarizing influence. (Sign inverting feedback)

Question 13

How do H cells influence bipolar cells?

Answer 13

H cells make a sign inverting SYNAPSE onto bipolar cells (feed forward)

Ex: if the bipolar cell is depolarizing, the H cell feed forward influence causes the bipolar cell to depolarize less.

Question 14

How do H cells influence cones?

Answer 14

They make a sign inverting FEEDBACK onto cones.

Question 15

In the dark, H cells are relatively ____ by glutamate transmission from photoreceptors onto the H-cell inotropic glutamate receptors.

Answer 15

depolarized.

Question 16

With white light stimulation, photoreceptors hyper polarize and release (more or less) glutamate, resulting in a relative H cell hyper polarization.

Answer 16

Less

Question 17

What is the “neural effect, synapse” that horizontal cells have on photoreceptor cells? How does this control the magnitude of the photoreceptors effects?

Answer 17

When a horizontal cell hyper polarizes, it feeds back onto the photoreceptor cell, resulting in a depolarizing influence on the photoreceptor. This is called the neural effect synapse.

Prevents PR from sending too powerful of a signal. Horizontal cells tell PR cells to calm down.

Question 18

Glutamate release of cones when in dark and when activated by light

Answer 18

When in the dark, the photoreceptor cell is relatively depolarized and releasing a lot of glutamate.

When in the light, the photoreceptor cell hyper polarizes and releases less glutamate. This causes the H cells and bipolar cells to also hyper polarize.

The H cell in turn, causes the PR cells and bipolar cells to relatively depolarize. Basically calm their signal.

Question 19

____ are the most numbers bipolar cell types

Answer 19

Rod Bipolars. This is likely because rods are way more numerous than cones.

Question 20

List the 6 bipolar cell types, their receptor channel type, and how many inputs they receive

Answer 20

1. Rod bipolar: most common. Metabotropic. Input from many cells.
2. Invaginating midget. Metabotropic. Input from 1 cone.
3. Flat midget. Ionotopic. Input from 1 cone.
4. Diffuse bipolar. Metabotropic and inotropic. Input from 5-20 cones.
5. Blue bipolar. Metabotropic. 1 strongly, 1 weakly.

Question 21

There are at least __ different subtypes of diffuse bipolar cells.

Answer 21

6

Question 22

Metabotropic channels cause

Answer 22

Cause ion channels to close. “on” center pathway. Less glutamate released. (results in hyper polarizing nearby cells, activating them)

Question 23

Ionotropic channels cause

Answer 23

Cause ion channels to open. “off” center pathway. More glutamate released. (results in depolarizing nearby cells)

Question 24

On bipolar cells. Are they hyper polarized or depolarized in the dark vs light.

Answer 24

On bipolar cells are opposite of a lot of others.

In the dark, they are hyper polarized. In the light, they become depolarized.

Question 25

Off bipolar cells. Are they hyper polarized or depolarized in the dark vs light?

Answer 25

Dark- depolarized

Light- hyper polarized

Question 26

Each rod-bipolar cell makes contact with how many rods?

Answer 26

30-50

Question 27

Lateral inhibition

Answer 27

The influence of each rod that contacts a given bipolar is reduced by an amount that depends on the activity of the surrounding rods.

Question 28

are rod-bipolars at type of on bipolar or off bipolar?

Answer 28

On bipolar.
In the dark, they are hyper polarized.
In the light, they depolarize by graded response.

Question 29

Connection between rod and ganglion cell

Answer 29

Rod- rod bipolar- A II amacrine- cone bipolar- ganglion cell

Question 30

How do A II respond to changes in light?

Answer 30

They are involved in transferring rod information to the ganglion cells through the cone bipolar cell.

Therefore, they are most active as light increases from total darkness to mesonic levels.

Once photopic light levels are reached, they have to get out of the way so cones can connect to the ganglion cells. Therefore, they decrease again to scotopic levels.

Question 31

What hormone decreases A II coupling?

Answer 31

Dopamine. Therefore, dopamine is necessary to see in photopic light conditions. Allows cone system to work better.

Parkinsons

Question 32

Why does Parkinsons affect vision?

Answer 32

Parkinsons occurs because the body does not produce/release enough dopamine. Dopamine is needed to reduce the levels of Amacrine II coupling.

A II coupling is used to transfer rod info to the ganglion cells when it is dark- mesopic lighting. When it becomes bright out, they need to decrease the coupling so the cones can be in contact with the ganglion cells. If dopamine isn’t released, A II coupling levels will not change. Therefore, cones will not be able to interact with the ganglion cells= bad photopic vision

Question 33

Dendrites of diffuse bipolar spread out laterally to receive from about ___ L and M cones

Answer 33

5-10 M and L cones

Question 34

Where are midget bipolar located and how many cones does their dendrites come in contact with?

Answer 34

Located in central retina. Receives info from 1 cone.

Question 35

S cone off midget bipolar cells make ___ contacts with ___ pedicles

Answer 35

Make flat contacts with S cone pedicles.

Morphology similar to M and L midget bipolar.

Dark- depol
light- hyperpolarization

No S cone ON midget bipolar cells have been identified in primates

Question 36

Bipolar type differs depending on to which photoreceptors they connect and upon where in the ___ that they synapse

Answer 36

IPL (Between INL and Ganglion cell layer)

Bipolar cells that synapse closer to the ganglion cell layer within the IPL are considered “on.”

Bipolar cells that synapse further from the ganglion cell layer within the iPL are considered “off.”

(Rod bipolar axons are located even closer to the ganglion cell layer than the on bipolar cells)

Question 37

Which two cell types demonstrate a center-surround receptive field?

Answer 37

Bipolar cells and ganglion cells.

Question 38

What does center-surround receptive field mean?

Answer 38

Stimulation of the center of the receptive field generates one response and stimulation of the surround of the same cell generates the opposite response.

Question 39

Another name for Center-surround receptive field

Answer 39

Difference of Gaussian (DOG), lateral inhibition