Photoreceptor Bipolar Connections Flashcards
Horizontal cells in the OPL form synapses with __ and __ and communicate with ___.
They form synapses with rods and cones and communicate with bipolar cells.
The rod spherule has ___ invagination with ____ synaptic ribbons with invaginating contacts.
One invagination with 1-2 ribbons.
The cone pedicle has ___ synaptic ribbons with invalidating contacts. Each invagination contains __ horizontal cell processes and ___ or more bipolar cell processes.
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.
Synaptic ribbons do what
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.
What can bind to the single invagination of rod spherules?
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.
Which cells transmit visual info by graded potentials?
Photoreceptors, horizontal cells, bipolar cells and (most likely) amacrine cells
Two types of graded potentials
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.
Excitation vs inhibition of light
Excitation- the onset, or increase of light
Inhibition- The offset, or decrease of light
Light on in the photoreceptor causes it to ____
Light off in the photoreceptor causes it to ___
Hyperpolarize Depolarize (relatively. The value does not become positive, but less negative)
Light on in the horizontal cell causes it to ____
Light off in the horizontal cell causes it to ___
Hyperpolarize
Depolarize
Receptive fields of horizontal cells vs photoreceptor filds
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.
After photoreceptor cells are stimulated with light, they will hyperpolarize and stimulate Horizontal cells. How do horizontal cells respond?
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)
How do H cells influence bipolar cells?
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.
How do H cells influence cones?
They make a sign inverting FEEDBACK onto cones.
In the dark, H cells are relatively ____ by glutamate transmission from photoreceptors onto the H-cell inotropic glutamate receptors.
depolarized.
With white light stimulation, photoreceptors hyper polarize and release (more or less) glutamate, resulting in a relative H cell hyper polarization.
Less
What is the “neural effect, synapse” that horizontal cells have on photoreceptor cells? How does this control the magnitude of the photoreceptors effects?
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.
Glutamate release of cones when in dark and when activated by light
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.
____ are the most numbers bipolar cell types
Rod Bipolars. This is likely because rods are way more numerous than cones.
List the 6 bipolar cell types, their receptor channel type, and how many inputs they receive
- Rod bipolar: most common. Metabotropic. Input from many cells.
- Invaginating midget. Metabotropic. Input from 1 cone.
- Flat midget. Ionotopic. Input from 1 cone.
- Diffuse bipolar. Metabotropic and inotropic. Input from 5-20 cones.
- Blue bipolar. Metabotropic. 1 strongly, 1 weakly.
There are at least __ different subtypes of diffuse bipolar cells.
6
Metabotropic channels cause
Cause ion channels to close. “on” center pathway. Less glutamate released. (results in hyper polarizing nearby cells, activating them)
Ionotropic channels cause
Cause ion channels to open. “off” center pathway. More glutamate released. (results in depolarizing nearby cells)
On bipolar cells. Are they hyper polarized or depolarized in the dark vs light.
On bipolar cells are opposite of a lot of others.
In the dark, they are hyper polarized. In the light, they become depolarized.
Off bipolar cells. Are they hyper polarized or depolarized in the dark vs light?
Dark- depolarized
Light- hyper polarized
Each rod-bipolar cell makes contact with how many rods?
30-50
Lateral inhibition
The influence of each rod that contacts a given bipolar is reduced by an amount that depends on the activity of the surrounding rods.
are rod-bipolars at type of on bipolar or off bipolar?
On bipolar.
In the dark, they are hyper polarized.
In the light, they depolarize by graded response.
Connection between rod and ganglion cell
Rod- rod bipolar- A II amacrine- cone bipolar- ganglion cell
How do A II respond to changes in light?
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.
What hormone decreases A II coupling?
Dopamine. Therefore, dopamine is necessary to see in photopic light conditions. Allows cone system to work better.
Parkinsons
Why does Parkinsons affect vision?
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
Dendrites of diffuse bipolar spread out laterally to receive from about ___ L and M cones
5-10 M and L cones
Where are midget bipolar located and how many cones does their dendrites come in contact with?
Located in central retina. Receives info from 1 cone.
S cone off midget bipolar cells make ___ contacts with ___ pedicles
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
Bipolar type differs depending on to which photoreceptors they connect and upon where in the ___ that they synapse
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)
Which two cell types demonstrate a center-surround receptive field?
Bipolar cells and ganglion cells.
What does center-surround receptive field mean?
Stimulation of the center of the receptive field generates one response and stimulation of the surround of the same cell generates the opposite response.
Another name for Center-surround receptive field
Difference of Gaussian (DOG), lateral inhibition
