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Neurophysiology > Neurophysiology: Lecture 4 > Flashcards

Neurophysiology: Lecture 4 Flashcards

1
Q
  1. What are the 4 Major Functions of the Retina?
A
  1. Detecting Motion
  2. Detecting Local changes in illumination
  3. Discriminating Color
  4. Responding to Ambient Light
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2
Q

Detecting Local Changes in Illumination (1)

Receptive Fields

  1. What is a Receptive Field?
    a. Cells can become 1 of 2 things.
  2. What are small receptive fields needed for?
  3. Large receptive fields needed for?
  4. What does a Receptive Field of a given cell depend on?
  5. How are complex receptive fields built up?
A
  1. an Area of the ENTIRE Visual Field to which a Cell Responds.
    a. Excited or Inhibited
  2. High Acuity Vision. (Midget Ganglion Cells)
  3. Better for Light Capture (Rod Vision) and Detection of Motion. (These are Parasol Ganglion Cells)
  4. Depends on the Connections it Makes with other cells…aka, the “Circuitry”
  5. By Combining Simpler Receptive Fields
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3
Q

Detecting Local Changes in Illumination (2)

Receptive Fields of Ganglion Cells

  1. Center Surround Organization
    a. Light in the center of a receptive field will produce what type of response?
    b. And light in the Surrounding ANNULUS will produce what type of Response?
    c. This is used by what cells?
  2. Stimulation of the Center can produce what 2 things?
  3. This organization is produced through what process?
A
  1. a. 1 type of response (like Stimulation)
    b. Produce the opposite response
    c. Mainly Ganglion Cells: either Midget or Parasol
  2. Excitation (ON-Center) or Inhibition (OFF-Center)
  3. Lateral Inhibition
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4
Q

Detecting Local Changes in Illumination (3)

Lateral Inhibition

  1. Define
  2. Purpose?
  3. What cells are mainly responsible for mediating Lateral Inhibition in the Retina?
  4. What other cells may help in this process?
A
  1. Attenuation of the response to a Local Stimulus when the areas adjacent to it are also stimulated
  2. to allow detection of LOCAL VARIATIONS in Illumination
  3. Horizontal Cells
  4. Amacrine Cells
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5
Q

Detecting Local Changes in Illumination (4)

Cellular Basis of Lateral Inhibition

  1. Light comes in and does what to the Photoreceptor?
    a. This leads to Decreased Release of what molecule?
  2. This decreased release causes what to occur in the cell?
    a. Occurs thru what Receptor?
  3. What does this lead to?
  4. Decreased release of this molecule will do what?
  5. Stimulation of a Bipolar cell by a Photoreceptor will be LESS EFFECTIVE when what happens?
A
  1. Repolarizes the Photoreceptor
    a. Decreased Glutamate Release
  2. Causes Hyperpolarization of Horizontal Cell Arbor
    a. Thru the IONOTROPIC Glutamate Receptor
  3. Hyperpolarization of a Horizontal Cell Arbor Causes Decreased release of GABA
  4. Decreased GABA release DISINHIBITS (Depolarizes) ALL other Photoreceptors contacted by that Arbor
  5. if the Horizontal cells that are part of the synapse have also been stimulated.
    a. Juxtaposition of their processes in the cleft makes inhibition more effective.
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6
Q

Detecting Local Changes in Illumination (5)

Lateral Inhibition Example

  1. A Narrow beam of light will do what to the Highlighted rod?
  2. A Wider beam of light will stimulate what exactly?
    a. Stimulating the SURROUND RODS will do what?
  3. So the Net Output due to Stimulation of the Highlighted rod will become what, with the Wider Beam?
A
  1. Will Stimulate the Highlighted Rod.
  2. Both the Highlighted rod and the other rods around it.
    a. Will DECREASE Activity in the Horizontal Cell Arborization
  3. Will be Reduced with the Wider Beam due to LATERAL INHIBITION
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7
Q

Detecting Local Changes in Illumination (6)

Key Elements of Response

  1. Response has what 2 types of components?
  2. Response reflects what exactly?
  3. Poor response in what kind of lighting?
A
  1. Transient and Sustained Components
  2. The Difference in Illumination in “Center” Relative to that in the “surround”
  3. In Diffuse Illumination: Simultaneous Stimulation of Center and Surround
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8
Q

Detecting Local Changes in Illumination (7)

Function of Center-Surround Organization

  1. What does it detect?
    a. Most responsive to Stimuli Restricted to what area of the receptor field?
    b. Less responsive to what?
    c. When is it at its HIGHEST RESPONSE?

d. Troxler Phenomenon: Define
2. Information on Local Changes will be used where?

A
  1. Changes in Light
    a. to the CENTER of Receptive Field
    b. to Concurrent Stimuli in BOTH CENTER and SURROUND or a stimulus that covers BOTH
    c. At Onset and/or Offset
    d. Image Stabilized on Retina Fades in a few seconds
  2. At HIGHER LEVELS of the VISUAL SYSTEM for MORE COMPLEX PROCESSING
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9
Q

Detecting Local Changes in Illumination (8)

Hermann Grid Illusion

  1. White Lines appear Less bright at what location?
  2. Why does this happen?
A
  1. Where they CROSS

2. Because more of the Surround Region is STIMULATED at CROSSING, so the RESPONSE is MORE INHIBITED There.

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10
Q

Discriminating Color (1)

The Principle of Univariance

  1. What is it?
  2. Photoreceptors have a Higher Probability of being stimulated by what?
  3. the only way to detect color (different wavelengths of light) is to KEEP TRACK of what?
A
  1. ANY Photon that causes the Isomerization of a Photopigment Induces the SAME response REGARDLESS of its WAVELENGTH
  2. by Light of Certain Wavelengths (L, M, and S)
  3. of the Relative Stimulation of Photoreceptors with different response characteristics
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11
Q

Discriminating Color (2)

Rods and Cones

  1. Similar processes are involved in what 2 things?
  2. Rods contain what molecule?
    a. What is it exactly?
  3. Cones contain what?
A
  1. In Phototransduction in Rods and Cones
  2. Rhodopsin
    a. Retinal linked to an Opsin (OPN2)
  3. Retinal Linked to Other Opsins (All OPN1 with either LW, MW, or SW)
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12
Q

Discriminating Color (3)

Color Opponency Theory

  1. Formulated by whom?
    a. Based on what?
  2. What 4 colors are SPECIAL COLORS?
    a. All other colors are made from what?
    b. But, one doesn’t experience what 2 things?
  3. What colors are opponent colors?
  4. The Neural Circuitry for Color Opponency Requires the ability to distinguish b/w what 4 things?
A
  1. Hering in 1892
    a. on Subjective Experience
  2. Red, Green, Yellow, Blue
    a. from mixtures of these colors
    b. Red-greens or Yellow-blues
  3. Red and Green are opponent colors; Yellow and blue are as well
  4. Red, Green, Yellow, Blue
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13
Q

Discriminating Color (4)

Blue-Yellow Circuitry

  1. What ganglion cells have an ON Center and an OFF Center?
    a. S Cone Bipolar Cells receive inputs only from what?
    b. Midget and Diffuse Bipolar Cells receive input from what 2 cones?
  2. What light ALONE provides Max stimulation of these Ganglion cells?
    a. Presence of OTHER Wavelengths Produces what kind of stimulation?
A
  1. Small Bistratified Ganglion Cells. ON CENTER (S Cone BIPOLAR cell driven) and OFF Center (Diffuse Bipolar Cell Driven)
    a. Only from S Cones
    b. From L and M Cones
  2. Blue Light ALONE
    a. Produces OFF Center Stimulation
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14
Q

Discriminating Color (5)

Detecting Red-Green (L-M) Light

  1. Midget Ganglion cells receive input from what cells?
    a. And those cells receive input from what?
  2. Determination of what Type of Cone it is has to be made where?
  3. Yellow light can be detected as what?
A
  1. from Midget Bipolar Cells
    a. From a SINGLE L or M Cone
  2. At a Higher Level in the Visual System, possibly by Visual Experience. (L or M cone…which is it.)
  3. As an Equivalent Stimulation of L and M Ganglion Cells
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15
Q

Discriminating Color (6)

Higher Order Color Opponent Cells

  1. Center-Surround Receptive Field: Does what?
  2. Color Opponent Receptive Field: Does what?
    a. What else does it detect?
A
  1. Responds to Light in the CENTER of the FIELD and in the Surround in an ANTAGONISTIC FASHION
  2. Center and Surround respond to DIFFERENT Wavelengths in an ANTAGONISTIC FASHION
    a. Allows us to DETECT Color “Edges”
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16
Q

Discriminating Color (7)

Color “Edge” Detection

  1. What hits on center?
  2. What hits surround?
A
  1. Green (M On)

2. Red (L Off)

17
Q

Discriminating Color (8)

Cone Distribution in Retina

  1. How do we see it?
    a. Why is it Pseudocolored? (Based off of what)
    b. Distribution type?
  2. How do Ratios vary?
    a. Do they Affect Color Discrimination?
  3. What may help in Identifying Similar Photoreceptor Types?
A
  1. Using Adaptive Optics
    a. Its based of off Densitometry
    b. Non-Random Distribution of L and M Cone Types
  2. Vary Greatly
    a. No.
  3. Clumping
18
Q

Discriminating Color (9)

Kollner’s Rule

  1. What disease types result in BLUE-YELLOW Color Defects?
  2. Disease Types that Result in RED-GREEN Defects?
  3. Detection of what wavelengths is a RETINAL PROCESS?
  4. Other wavelength detection depends on what?
  5. Is this detection Absolute?
  6. What can be used to Detect Blue-Yellow Field Deficits?
A
  1. Outer Retinal Diseases (and media changes)
  2. Diseases of the Inner Retina, Optic Nerve, Visual Pathway, and Visual Cortex
  3. Of Blue (S) Wavelengths (More easily disturbed by Retinal Pathology)
  4. Red (L) and Green (M) detection carried out at a HIGHER LEVEL (Visual Cortex): More easily disturbed by Pathology that Effects TRANSMISSION of Info out of the Retina
  5. No. It isn’t. It doesn’t Apply in Glaucoma
  6. Short-Wavelength Automated Perimetry (SWAP)
19
Q

Motion Sensitivity (1)

  1. What cells have been studied most in the Rabbit?
    a. What cells and where are they found, can respond to ON and OFF Stimuli?
    b. What about Dark or Light Stimulus?
  2. Somewhere in the system, there must be what?
    a. Inhibition follows stimulus in what direction?
    b. Inhibition proceeds the Stimulus in what direction?
  3. Motion sensitivity may be provided by what cells?
A
  1. On-Off Direction-sensitive Ganglion cells
    a. Bistratified Dendritic Arbor in Inner Plexiform Layer
    b. Same directionally Sensitive Response to Dark or Light Stimulus moving anywhere in the Receptive Field
  2. Asymmetry so that inhibition is displaced laterally relative to the stimulus
    a. in the Positive direction
    b. In the null Direction
  3. Starburst Amacrine Cells
20
Q

Response to Ambient Light

  1. What cells receive inputs DIRECTLY from RODS and CONES?
  2. What are they activated by?
  3. They’re not influenced by what 2 cells?
    a. What does this mean?
  4. What 2 things might they control?
A
  1. Biplexiform Ganglion Cells
  2. By Light
  3. Not influenced by Bipolar or Amacrine Cells
    a. Less Processing of Signal
  4. Pupil Diameter and the Periodicity of Diurnal Rhythms
21
Q

Retinal Function Overview

  1. Retina is Largely a Feature Detector Rather than a Light detector. What 3 things?
  2. Feature detection Relies PRIMARILY on what?
  3. Detection of what light is LARGELY a RETINAL FUNCTION and can be used Diagnostically?
A
  1. a. Local Variations in illumination
    b. Color
    c. Movement
  2. on Lateral Inhibition
  3. Blue Light

Neurophysiology (4 decks)

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