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Neuroscience I > Vision Lecture (Dr. Karius) TEST 2 > Flashcards

Vision Lecture (Dr. Karius) TEST 2 Flashcards

1
Q

Challenge: Focus the Image onto the Retina

A
  • If the OBJECT is FAR AWAY, the Light Rays HAVE DIVERGED Far Enough that ONLY PARALLEL Light rays ENTER the Eye. Therefore it doesn’t take much REFRACTION to MAKE the Parallel Rays FOCUS on the RETINA
  • If the OBJECT is NEARBY, the Light Rays are STILL DIVERGING! It takes MORE REFRACTION (Bending) to make the Diverging Rays FOCUS on the RETINA!
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2
Q

To Focus the Image on the Retina, the eye uses REFRACTION

A
  • The CORNEA is the FIRST SITE in the Eye where Refraction Occurs
  • It bends the LIGHT the MOST of any Structure in the Eye and ACCOUNTS for 2/3 of the ability of the Eye to BEND LIGHT
  • The amount of BENDING is FIXED (We cant control it)
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3
Q

The Lens adds a Variable Degree of Refraction

A
  • We need VARIABLE REFRACTION provided by the Lens because of the DIFFERENT DISTANCES of the Objects that the eye sees
  • The Lens can addict its SIZE and SHAPE depending on how FAR AWAY or CLOSE the Object is
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4
Q

Accommodation

A

REQUIRES:

1) Cilairy Muscle
2) Suspensory Ligaments
3) Lens Itself

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5
Q

Near Vision required CONTRACTION of the Ciliary Muscle

A

1) As the CILIARY MSUCLE CONTRACTS, the TENSION on the Suspensory Ligament is RELEASED!
2) The Suspensory Ligaments become SLACK
3) The Natural Elasticity of the LENS causes the LENS to become ROUNDER

4) The INCREASED CURVATURE of the Lens INCREASES the REFRACTIVE POWER of the LENS
- In Young Kids, this ADDS about 20 Diopters

  • In Young Adults, Loss of Elasticity results in a total Strength of about 10 Diopters
  • By the 50’s, the LOSS of Elasticity means that the Lens may only be able to ADD 1 Diopter

*** The INCREASED CURVATURE of the Lens allows the LIGHT RAYS from a Nearby OBJECT to be BENT sufficiently to Bring them INTO FOCUS on the RETINA!!!!! ****

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6
Q

FAR Vision required RELAXATION of the Ciliary Muscles

A

1) As the Ciliary Muscle RELAXES, the TENSION on the Suspensory Ligaments is INCREASED
2) The Suspensory Ligaments becomes TAUT
3) This PULLS the LENS into a FLAT POSITION
4) The Decreased Curvature of the lens DECREASES the REFRACTIVE POWER of the Lens!!!

**** If the Object is FAR AWAY, LESS Bending of the PARALLEL (or Nearly so) Light Rays is Required, the LENS needs to be FLATTER!!!!!!!!!!

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7
Q

Near Vision rewired TWO OTHER Changes

A

The NEAR RESPONSE Includes:
1) CONTRACTION of the Ciliary Muscles as Described

2) CONVERGENCE of the Eyes to the POINT of FOCUS

3) CONSTRICTION of the PUPIL!!!!!!!!!!!!
- By constricting the Pupil, we Reduce the Opening for LIGHT to ENTER
- This Eliminates some of the DIVERGING Light Rays
- Allows us to FOCUS BETTER

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8
Q

The Retina

A
  • There are MULTIPLE LAYERS of Cells in the Retina
  • There are MULTIPLE CELL Types
    a) Photoreceptors (Rods and Cones)
    b) Bipolar Cells
    c) Ganglion Cells
    d) HORIZONTAL CELLS
    e) AMACRINE CELLS

* Photoreceptors, Bipolar Cells, and Ganglion Cells make up the DIRECT PATHWAY from the Optic Nerve to the Brain ***

  • The Light must PASS THROUGH ALL of the Layers EXCEPT ONE before getting to the Photoreceptors
  • That creates some DISTORTION of the Iamge. The RETINA Itself will take care of most of that
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9
Q

Retina- Vertical PAthway

A
  • Composed of:
    a) Photoreceptor
    b) Bipolar Cell
    c) Ganglion Cell
  • This is the Pathway for RELAYING the VISUAL INFORMATION to the Brian
  • The CIRCUIT for the CONES seems to be the “BASE” for ALL VISION
  • The Photoreceptors (Rods or Cones) have a CONSTANT RELEASE of GLUTAMATE
    a) When it is DARK (No Stimulation): the release of GLUTAMATE is HIGH!!!

b) When a Photon activates the Photoreceptor (Light): the release of GLUTAMATE DECREASES!!!

Dark: INFLUX of Na+ (DEPOLARIZATION)

Light: Shuts Down Na+ Channel (HYPERPOLARIZATION)

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10
Q

The Vertical Pathway for Cones

A

STEP 1: Photoreceptors STRUCK by a PHOTON of Light

STEP 2: DECREASES Neurotransmitter RELEASE onto a BIPOLAR CELL!!!!!
- The Neurotransmitter is GLUTAMATE!!!!

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11
Q

All Bipolar Cells are NOT the Same

A

1) ON Center Bipolar Cells

2) OFF Center Bipolar Cells

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12
Q

ON-Center Bipolar Cells

A
  • Activation of Photoreceptor in the CENTER of the Bipolar Cell’s Receptive Field causes DEPOLARIZATION of the Bipolar Cell
  • Activation of the Photoreceptor in the SURROUNDING Region causes HYPERPOLARIZATION of the Bipolar Cell
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13
Q

OFF-Center Bipolar Cells

A
  • Activation of a Photoreceptor in the CENTER of the Bipolar Cell’s Receptive Field causes HYPERPOLARIZATION of the Bipolar Cell
  • Activation of a Photoreceptor in the SURROUNDING REGION causes DEPOLARIZATION of the Bipolar Cell
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14
Q

Vertical Pathway for CONES

ON-Center Bipolar Cell

A

If the Photoreceptor activates an ON-Center Bipolar Cell:

  • ** METABOTROPIC RECEPTOR is ACTIVATED!!!!!!
  • Neurotransmitter release causes a DECREASE in Cation Influx!!!!!!!!!!!!!!!!!!!!!!!!!
    a) Remember: Activation of the Photoreceptor DECREASES Neurotransmitter Release

b) So in the DARK, the ON-Center Cell is HYPERPOLARIZED!!!!!!!!
c) With LIGHT, the release of GLUTAMATE from the Photoreceptor DECREASES, so the CATION current INCREASES and the ON-Center Cell is DEPOLARIZED!!!!!!!!!!!!

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15
Q

Vertical Pathway for CONES

OFF-Center Bipolar Cell

A

If the Photoreceptor activates an OFF Center Bipolar Cell:

  • ** AN AMPA RECEPTOR is activated!!!!***
  • Neurotransmitter Release causes an INCREASE in CATION INFLUX!!!!!!!!!!!!!!!!!!!!!!
    a) Remember: Activation of the Photoreceptor DECREASES Neurotransmitter Release

b) So in the DARK, the OFF-Center Cell is DEPOLARIZED
c) With LIGHT, Glutamate release from the Photoreceptors DECREASES, the AMPA Receptor is NOT Activated and the OFF-CEnter Cell is Hyperpolarized!

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16
Q

Vertical Pathway for CONES

A

Ganglion Cells are also ON-Center or OFF-Center (Whatever the Connecting Bipolar Cell is)
- The BIPOLAR Cell release GLUTAMATE to Excite the Ganglion Cell

  • Ganglion Cell AXONS become the Fibers on the OPTIC NERVE

ACTION POTENTIALS**

  • Relies on GLUTAMATE as Neurotransmitter
17
Q

The Vertical PATHWAY for RODS

A

Composed of the:
- Many RODS

  • Converge on One ON-CENTER BIPOLAR CELL!!!!!!!!
  • Which then Synapses on an A11 AMACRINE CELL!!!!!!!
  • Which Synapses on a CONE ON-CENTER BIPOLAR Cell!!!!!!!
  • Which then activates a GANGLION CELL!!!!!

** Remember that RODS do Vision in LOW-LIGHT Situations, we need MANY Rods to Converge on a Bipolar Cell to INCREASE our Chances of seeing what we need to see!**

18
Q

Refining the Signal in the Retina

A
  • Role of ON and OFF-Center Cells
    a) These Two Types of Cells help us INCREASE the ability to DETECT EDGES and so they SHARPEN our VISION

b) The ON-Center Cell tells us where something is
c) The OFF-Center Cell tells us where it ends
- The AMACRINE and HORIZONTAL Cells ADD to that by providing INHIBITORY Signals that Modify the activity of Neighboring Photoreceptors, Bipolar Cells, or Ganglion Cells (Depending on what Amacrine or Horizontal cell you’re talking about)

19
Q

Sending the Signal to the Brain

A
  • Action Potentials OCCUR in GANGLION CELLS
  • The Axons from the Ganglion Cells will become the Fibers of the OPTIC NERVES

***The RETINA from EACH EYE sees TWO DIFFERENT Visual Fields!!!!!

20
Q

Reconstructing the Visual Image

A

1) LEFT TEMPORAL RETINA:
- Activated by Light coming from the RIGHT VISUAL FIELD!!!!

2) RIGHT NASAL RETINA:
- Activated by Light coming from the RIGHT VISIAL FIELD!!!!

3) RIGHT TEMPORAL RETINA:
- Activated by Light coming from the LEFT VISUAL FIELD!!!!

4) LEFT NASAL RETINA:
- Activated by Light coming from the LEFT VISUAL FIELD!!!

21
Q

Reconstructing the Visual Image Diagram

A
  • At the OPTIC CHIASM, the Axons from the NASAL RETINA on each side will CROSS and join the Axons from the TEMPORAL RETINA!!!
  • This was ALL the Information fro the RIGHT VISUAL FIELD is Sent to the SAME PART of the BRAIN (IN Case of the Right Visual Field, the LEFT SIDE of the Brain!!!!)
22
Q

Reconstructing the Visual Image: The LATERAL GENICULATE BODY

A
  • The Axons then TRAVEL to and SYNAPSE in the LATERAL GENICULATE BODY
  • ON and OFF-CENTER Cells exist in the LGN as well
  • FUNCTIONS of the LGN:
    1) CONTROL the MOTION of the EYES:
  • So they converge on the DESIRED Point of Interest (CONVERGENCE/ DIVERGENCE)

2) CONTROL FOCUSING:
- So that the Image we are Interested in is in the BEST FOCUS POSSIBLE

  • *** 3) IDENTIFY Major Elements WITHIN OUR VISUAL IMAGE:
  • And send that Identification to the Cortex *****

4) Identify MOTION:
- Identify Motion WITHIN OUR VISUAL Image (MUSCLE RESPONSES!!!!!!!!!!)

23
Q

Reconstructing the Visual Image: The PRIMARY Visual Cortex (V1)

A
  • The NEOCORTEX is divided into 6 Layers of Cells (Some of which have SUB-LAYERS)
  • Layers 1, 2, and 3 allow NETWORKING between V1 and the Other Parts of the Cortex
  • Layer 4 RECEIVES INPUTS from the LGN
  • Layer 5 and 6 send Information BACK to the LGN
24
Q

Reconstructing the Visual Image: The PRIMARY Visual Cortex (V1) Cont

A
  • From a FUNCTIONAL Standpoint, the Cortex is composed of Columns that start from the Surface of the Cortex and EXTEND through ALL 6 Layers of Cells
  • Each Column does a DIFFERENT JOB
    a) If One Column Detects Horizontal Edges, a Neighboring Column Detects EDGES Oriented at 30 Degrees!!!

******* The MAJOR Job of V1 is to IDENTIFY THE EDGES/ CONTOURS of the Components in Our Visual Image!!!!!!!!!!!!!!!**

25
Q

Reconstructing the Visual Image: The PRIMARY Visual Cortex (V1) Cont

MACULA

A
  • There are a lot of Columns in the V1 that RECEIVE INPUT from Photoreceptors in the MACULA (In part, because that is the Place where Receptor Density is the GREATEST)
  • The PERIPHERAL Regions of the Retina have MUCH LESS AREA in V1 devoted to them (few Receptors, many of which CONVERGE onto the SAME BIPOLAR CELLS)
26
Q

Reconstructing the Visual Image:

V2

A
  • The MAJOR Job of V2 is to IDENTIFY DISPARITIES in the VISUAL IMAGES PRESENTED by the TWO EYES!!!!!!!!!
  • Disparities between what the two eyes detect are USED for DEPTH PERCEPTION!!!!!
27
Q

Reconstructing the Visual Image: Color Vision - the Role of V1

A
  • Within the Columns, there are COLLECTIONS of Neurons known as “BLOBS” that ENABLE COLOR DETECTION!!!!
  • Accurate Color Detection depends on the INPUT from all THREE SETS of CONES!!!!
  • Because of the OVERLAP in the Sensitivities of the OPSINS
    (The ONE EXCEPTION is once we get to the RED, there is very little BLUE Light Activated!!!!!)
  • The Brain uses that OVERLAPPING Activity to arrive at a COLOR PERCEPTION
28
Q

Reconstruction of the Visual Image: Color Perception- Role of V4

A
  • The Major Job of V4 appears to be COMPLETE PROCESSING OF THE COLOR INPUTS!!!!!!
29
Q

Higher Processing of the Visual Image

A
  • Although we’ve done a lot of Processing of the Visual Image, based on what the Cortex has accomplished so far, we COULD NOT:
    1) Name the Image
    2) Copy the Image
    3) Aim at the Object in the Image
    4) Recognize your Husband/ Wife/ Mother/ Father

** We must rely on other areas of CORTEX to Interpret what the PRIMARY VISUAL CORTEX and associated areas have done so far!!!

DORSAL PATHWAY:
- Leaving the OCCIPITAL Coetex RELAYS Visual Information to the MOTOR CORTICES and enables us to COMPLETE MOTOR ACTS based on Visual Inputs!!!!!!

  • This Path allows you to Play Catch with you Friends…

VENTRAL PATHWAY:
- Relays VISUAL INFORMATION to areas of the Brain involved in HIGHER Processing of SENSORY INPUTS!!!!!!! The Integration of the Visual Input with other Sensory Inputs allows us to use that Visual Image to accomplish HIGHER ORDER FUNCTIONS, including Naming the Object and Copying the Object

30
Q

Higher Processing of Visual Inputs

A

Some details about this Processing:
1) Copying an OBJECT and Naming/ Recognizing it are SEPARATE FUNCTIONS and DAMAGE to the TEMPORAL LOBE can SELECTIVELY IMPAIR one WITHOUT HINDERING THE OTHER!!!!

2) Similar or Related Objects are ALL CODED for in LOCALIZED REGIONS of the Temporal Lobe
3) There is a SPECIALIZED AREA for Recognizing FACES!!!!

Neuroscience I (18 decks)

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