Lecture 3: Retinal Anatomy and Physiology Flashcards
1
Q
- % of Ganglion cells axons project to what structures? Purpose?
- Convergence: How many Photoreceptors?
a. Converge onto how many Ganglion Cells?
b. What does the retina have to do?
A
- 10%. To Subthalamic Structures. For NON VISUAL PROCESSES like PUPILLARY REFLEX!!
- 126 million
a. 1 million
b. condense and reorganize info from photoreceptors into something that can be transmitted thru the OPTIC NERVE!!!
2
Q
- Humans have 3 kinds of cones. What are they and what do each respond to?
A
- L Cone: Long Wavelengths: Reddish color.
- M Cone: Green Color
- S Cone: Bluish Color
3
Q
- How is Extracellular Recording done?
- Intracellular Recording?
- Graded neurons: Channels are what?
A
- Microelectrode placed REALLY CLOSE to the Neuron and records the APs
- Microelectrode pierces the NEURON’s Membrane and records the MEMBRANE POTENTIAL!! (IMportant when studying Neurons that produce GRADED POTENTIALS!!)
- VOLTAGE SENSITIVE: the opening and Closing is triggered by the MEMBRANE POTENTIAL
4
Q
Bipolar Cells
- 2 Classes: What do they do?
- ON Ganglion Cells: What do they do?
- OFF Ganglion Cells: What do they do?
A
- Those connected to cones: 2 basic classes: ones that depolarize in response to light, and ones that hyperpolarize!
- Depolarizing bipolar cells EXCITE ganglion: Increase firing rate in response to light
- Hyperpolarizing Bipolar Cells Excite Ganglion cells: DECREASE FIRING RATE when LIGHT is ON, and INCREASE FIRING RATE after light is TURNED OFF
5
Q
Inner Plexiform Layer
- To keep ON and OFF channels Separate, there are 2 discrete Sublaminae here: What are they?
A
- A (2 strata below the Amacrine Cell Bodies) (S1 and S2) (Hyperpolarizing Bipolar cells and OFF Ganglion Cells connect to the “A” sublamina)
and
- B (the other 3 strata stretching to Ganglion Cell Bodies) (S3-S5): Depolarizing Bipolar Cells and ON Ganglion Cells Connect in the “b” Sublamina
6
Q
Bipolar IPL: Interactions allowed b/w Basal Contacting Cone bipolar types and 1 set of Ganglion cells in Sublamina a
A
Invaginating contacting cone bipolar cells can only interact w/another set of ganglion cells branching in Sublamina b
7
Q
Ganglion Cells
- Each ganglion cell has a Receptive Field: What does it consist of? (CENTER of the field formed by what)
- What about Indirect input?
(What forms the SURROUND)
A
- Direct Input form Photoreceptors near the Ganglion cell thru Bipolar cells to form the CENTER of the RECEPTIVE FIELD
- thru HORIZONTAL cells to the Bipolar cell to the Ganglion Cell; Also other indirect input from bipolar cells further away thru AMACRINE Cells FORM the SURROUND of the receptive field
8
Q
Ganglion Cells (2)
- Direct input tends to do what?
- Indirect input tends to do what?
- Ganglion cells respond to what INSTEAD of INTENSITY of Light?
A
- Excite ganglion cells
- Inhibit them
- to Contrast
9
Q
Ganglion Cells (3)
- Ganglion cells fall into more than a dozen classes. Each looks at the retinal image thru a unique combo of what 3 things?
- Each class of ganglion cell then delivers the filtered neural image via the OPTIC NERVE to what?
A
- Spatial, Temporal, and Chromatic Filters
- to a specific Nucleus of Cells w/in the Brain that take care of some aspect of the Visually controlled motor behavior or visual perception
10
Q
Receptive Field of Ganglion Cells
- Finest Spatial pattern for Contrast being detectable depends on what?
- Ganglion cell receptive fields can’t be small than those of the individual cones, so the Retinal limit on Contrast detection is set by what?
- What about in the PERIPHERAL RETINA?
A
- on Size of the Largest receptive fields in the neurons that support contrast perception
- the Spatial filtering characteristics of Ganglion cell Receptive Fields
- The ganglion cell’s receptive field may be the UNION of SEVERAL DISJOINTED, WIDELY SPACED, Cone Receptive Fields
11
Q
- How do we get a MAXIMAL Response in an ON-Center Ganglion Cell?
- What if the SURROUND only is ILLUMINATED?
- What if Center and Surround are BOTH Illuminated?
A
- When the ENTIRE CENTER of the RECEPTIVE FIELD is ILLUMINATED!!!
- Then we get MAXIMAL INHIBITION
- Response is just ABOVE BASELINE (center effects are slightly stronger than the surround)
12
Q
Ganglion Receptive Fields
- Which type is less effective. Uniform illumination or a well placed small spot/line or edge passing thru the center of the cell’s receptive field?
A
- Uniform illumination of VF is less effective in activating a ganglion cell.
* The Orientation makes the Ganglion cells SENSITIVE to differences in the Level of Illumination across the receptive field or Luminance Contrast
13
Q
Ganglion cells
- What other roles do they have?
- Parvo Cells Show inhibition for what?
- Parvo cells show Excitation for what?
A
- Color and Luminance Processing
- (Decreased AP) for Short Wavelengths
- (INCREASED AP rate) for Long Wavelengths.
This is COLOR OPPONENCY
14
Q
Ganglion Cells: Receptive fields
- There can also be Input from what cones to the Center?
a. This is Antagonized by input from what cones?
b. Majority of Such cells are what? - Color-coded cells may have what?
A
- S-Cones to the center
a. From L and M Cones
b. Are Blue ON CENTER - May have excitatory Input from L Cones in the CENTER of the receptive Fields, and Inhibitory INput from M Cones in the Surround (RED ON CENTER); or vice versa (RED OFF Center)
15
Q
Ganglions: Other Roles
- Cells concerned with LUMINANCE PROCESSING may have what 2 types of responses?
- A Minority of Cells respond to what?
- Most Ganglion cells respond to what input?
A
- Sustained or Transient Responses
- to Overall Brightness rather than Contrast, w/a Very sustained Response
- to ROD input and Cone Input, and thus are activated in BOTH DAYTIME and NIGHTTIME CONDITIONS!!!
* Not every ganglion cell codes for brightness or color at the same time.
* Loss of Ganglion cell function w/age and time is GLAUCOMA
