Amacrine, RGCs, and their Functional Properties

Question 1

How many types of amacrine cell types are there?

Answer 1

Over 40 types.

Question 2

Why are amacrine cells important?

Answer 2

They integrate info coming from different areas of the retina.

They modulate info before it leaves the retina.

They have the ability to process information about time (Temporal domain) Ex; how the luminance is changing over time and space.

Transient or graded responses to light.

Question 3

How to categorize amacrine cells?

Answer 3

Can be described by the horizontal extent of their dendritic fields within the same layer. Ex: Narrow, small, medium, or wide field.

Can be described by the vertical extent of the dendritic fields. Monosaturated, bisaturated, or multi saturated (diffuse)

Question 4

Rod amacrine cells: 
1. What is their horizontal field extent? 
2 What is their vertical field extent? 
3. input
4. Output
5. Receptive field 
6. NT

Answer 4

Major carrier of rod signal to ganglion cells.

1. Narrow field.
2. Bistratified.
3. Input mostly from rod bipolar and other amacrine cells from sublmina B in the IPL (on)
4. Output to off-center ganglion cells whose dendrites are in the sublamina A (off)
5. On center, off surround.
6. Glyceine, inhibitory.

Question 5

A17 
1. What is their horizontal field extent? 
2 What is their vertical field extent? 
3. input
4. Output
5. Receptive field 
6. NT

Answer 5

Role is to increase light sensitivity at scotopic light levels. They collect signals from several thousand rod bipolar for amplification.

1. Wide- makes sense so they can contact the most rods.
2. Diffuse (multistratified)- makes sense. more contacts = more amplification
3. Input with reciprocal Rod bipolar from sublamina B (on). Some input from dopaminergic amacrines (A18)
4. Output with reciprocal rod bipolars in sublamina b (on)
5. On center, no surround. No region where you can take light away and cause the cell to respond differently.
6. GABA inhibitory.

Question 6

A18 role

Answer 6

Many connections to A II amacrine cells. Thought to control IPL gap junctions through dopamine release.

Question 7

Starburst amacrine cell. 
1. What is their horizontal field extent? 
2 What is their vertical field extent? 
3. input
4. Output
5. Receptive field 
6. NT

Answer 7

Responsive to motion. Foundation for directional tuning of motion sensitive neurons.

Occurs in mirror symmetric pairs of Ach-a and Ach-b:

Ach-a: Cell body found in INL. Dendrites stratify subliminal A (off)

Ach-b: Cell body found in GCL (weird, displaced). Dendrites stratify subliminal b (on)

1. Medium with tremendous overlap in dendritic trees.
2. vertical field ?
3. Cone bipolars and amacrines.
4. Output ?
5. A is off center/on surround. B is on center/off surround
6. Ach, excitatory

Question 8

Interplexiform Cells (IPCs)

1. Location
2. Input to IPL is from?
3. Output to OPL is to?
4. NT

Answer 8

1. Extends from inner to outer plexiform layer
2. Input to IPL is from amacrines
3. Output to OPL is to rod and cone bipolar cell bodies.
4. Gaba, inhib.

Question 9

How many ganglion cells are there

Answer 9

20 morphological different types identified

Question 10

2 main types of ganglion cells. Describe them based on morphological and physiological classification

Answer 10

1. Midget cells/P cells/Parvocellular system.

2. Parasol cells/M cells/Magnocellular system

Question 11

Which type of GC makes up 70% of the total GCs in the retina?

Answer 11

Midget (Make up 95% of the foveal GC and 45% of peripheral GC)

Question 12

How does the midget/P cell GC dendritic field and level of convergence change from the fovea, 2-6mm from fovea, and periphery?

Answer 12

• Projects to the parvocellular pathway of the LGN.
  1. Fovea. Extremely small dendritic fields. Allows for better spatial resolution. No convergence. 1 GC connects to 1 midget bipolar, which connects to 1 cone.
  2. 2-6mm from the fovea. Dendritic field becomes 10x larger. Contacts 2-3 midget bipolars, each of which is hooked up to a single cone.
  3. Periphery. very large dendritic field. Contacts 2-3 midget bipolars, each of which is hooked up to 2-3 cones.

Question 13

What is the dendritic field and convergence of Parasol/M GC?

Answer 13

Projects to the magnocellular pathway in LGN.

Parasol GC have lots of convergence. Mainly get input from aamcrine cells that are diffuse/multistriated. They receive 10-15x more input from rods compared to midget GCs.

Parasol cells are the only GCs that are active at low light levels. Therefore, they need a lot of convergence to get info.

Question 14

Are midget ganglion cells active at low light levels? Are parasol cells?

Answer 14

Midget ganglion cells are NOT active at low light levels.
Parasol cells are the only class of GC that remain active at low light levels.

Question 15

Koniocellular pathway in the LGN is related to the perception of

Answer 15

Color vision.

Question 16

Characteristics of the koniocellular pathway?

Answer 16

• related to the perception of color vision. have on center/off surround fields. Can be:
  +B/-Y, +R/-G, or +G/-R.
• Poor spatial resolution. Will not help detect 20/20
• Slow axons
• Intermediate contrast sensitivity and temporal resolution (not good at detecting fast flicker)
• Either sustained or transient responses

Question 17

Spatial linearity

Answer 17

When a neurons response to a complex stimulus within its receptive field is the sum of its responses to every part of that stimulus.

Question 18

How to test for spatial linearity

Answer 18

Make sure the bruins receptive field is filled by the stimulus. Use contrast reverse grating (switch back and forth). The measure the cells response while the grating is changing.

If at any phase, the neuron ceases to respond, it is called a null response which means the neuron is spatially linear. The cell does not detect the stimulus since it is cancelled out.

If the neuron continues to respond, and does not have a null position, it is spatially non linear.

Question 19

If a cell has a null response, what does that mean?

Answer 19

Means that while testing for spatial linearity, the cell stopped responding due to the stimuli cancelling each other out. The cell no longer can detect the stimuli.

Therefore, this cell is spatially linear.

Question 20

If a cell does not have a null response, what does that mean?

Answer 20

It means that the cell is spatially non linear.

Question 21

Examples of spatially linear cells and their field and response characteristics

Answer 21

Midget bipolar cells/P cells (parvocellular pathway)

has antagonistic receptive fields and has sustained responses

Question 22

Examples of spatially non linear cells and their field and response characteristics

Answer 22

parasol cells/ M cells (magnocellular pathway)

Lacks antagonistic field, transient responses

Question 23

All neurons with concentric, center/surround spatial antagonism function as __ filters

Answer 23

Band pass.

Ex: Bipolars, GCs, and LGN.

Question 24

Good contrast sensitivity and good visual acuity is mediated by what pathway

Answer 24

The midget/parvocellular pathway.
(An individual parasol cell is more sensitive to contrast than an individual midget cell, but midget cells outnumber parasols by 8:1) and contrast sensitivity is determined by pooled functions.