Midterm 1 - Vision Flashcards
Lobes of the Brain
3 Types of Neurons
Entire Spectrum of Electromagnetic Radiation
Visible Spectrum of Electromagnetic Radiation
Violet (400), Blue (450), Green (500), Yellow (550), Red (600)
Human Eye Anatomy
(Picture)
Fovea
- Retinal region of highest visual acuity.
- Color sensitive cones are the only type of photoreceptor in the fovea.
- There’s a round spot that the axons don’t go through so that there can be better signal transmission.
Choiroid (Eye)
Back of retina.
Optic Disk
- Exit point from the retina of fibers of ganglion cells that form the optic nerve.
- Produces a blind spot because no photoreceptors.
Cones vs. Rods
Cones
- Fovea
- Moderate/High Levels of Light
- Color Vision (hue)
- Acuity
Rods
- Peripheral retina
- Low Levels of Light
- Monochromatic Information
- Poor Acuity
- Greater # of rods than cones in retina overall
3 Varieties of Cones
- Short - Blue
- Medium - Green
- Long - Red
There’s more than 3 colors so there must be an overlap between the different wavelengths. Colors are produced by a combination of different short, medium and long cones firing.
Physical Structure of Human Retina
(Type and Order of Cells)
Back of retina –> photoreceptors (rods & cones) –> horizontal cells –> bipolar cells –> amarcrine cells –> ganglion cells
<————– LIGHT
Flow of Information From Photoreceptors
- Photoreceptor (Rod, Cone)
* Horizontal Cells - Bipolar Cells
* Amarcrine Cells - Ganglion Cells
–> Optic Nerve
Horizontal Cells
Interconnects adjacent photoreceptors and outer processes of bipolar cells.
Amacrine Cells
Interconnects adjacent ganglion cells and inner processes of bipolar cells.
What Happens When Light Hits Photoreceptors?
- Rhodopsin splits into opsin & retinal
- Phosphodiesterase degrades cyclic AMP
- Na+ channels close
- Hyperpolarization of photoreceptor
- Inhibition of release of glutamate onto bipolar cells
- Bipolar cells depolarized
- Bipolar cells release glutamate
- If enough glutamate is released, the ganglion cell will fire
Action Potentials: Photoreceptors, Bipolar & Ganglion Cells
Ganglion cells are the first cells to actually fire (i.e., have an action potential). Photoreceptors and bipolar cells merely have graded potentials.
What Happens to Photoreceptors in the Dark?
AKA, “Dark Current”
Photoreceptors are depolarized (active) and release glutamate, causing a hyperpolarization of the bipolar cell.
Vision Cranial Nerves
(4)
II. Optic (leaves eye)
III. Oculomotor (works iris, pupil)
IV. Trochlear (moves eyes up and down)
VI. Abducens (moves eyes side-to-side)
Optic Pathway
Visual of 12 Cranial Nerves
Visual Pathway
Diagram 2
Deficits to Visual Fields Caused by Cuts In Visual Pathways
Where is the LGN & What Eye Does it Receive Information From?
The LGN is located in the thalamus of each side of the brain and each LGN receives information from 2 different eyes!
Nasal Retinas
Cross
Temporal Retinas
Stay on same side.
6 Layers of the LGN
“See I? I see, I see”
Parvocellular Layers of the LGN
- “Small”
- 3, 4, 5, 6
- Form, color, fine details
- 1 cone feeds into 1 ganglion cell
- Fovea over-represented
Magnocellular Layers of the LGN
- “Big”
- 1, 2
- Many rods feeding into one ganglion cell
- Periphery
- Movement (larger visual field)
Retinotopic Organization in the LGN
More axons come from the fovea than from the periphery - that is why there are more parvocellular layers (i.e., the fovea is over-represented in terms of space).
Superior Colliculus
- Located in brainstem
- Allows for a “sampling of information”
- Visual information stops here before going to V1 from the LGN.
- Could be responsible for “blind sight” (a person can be blind due to an impairment in V1 and everything else can be intact - thus, they can move when a ball is thrown at their head).
Dorsal & Ventral Streams
(Visual Representation)
Dorsal Stream
- “WHERE”
- Goes up
- V1–>V2–>V5
- Movement
- Magnocellular
Ventral Stream
- “WHAT”
- Goes down
- V1–>V2–>V3–>V4
- Parvocellular
- Sends information of high acuity to the temporal cortex
3 Structures of Temporal Cortex Related to Vision
Receives information from the ventral stream and gets more refined as it moves along.
- Inferior Temporal - facial recognition
- Medial Temporal
- Medial Superior Temporal
Ice Cube Tray Model
(Class Drawing)
V1 (Striate Cortex)
V1 Simple Cells
Make out 180 degrees of orientation (e.g., horizontal line)
V2 Complex Cells
Orientation of a specific length
Top-Down Processing
“I’ve seen this before…”
Explains how the brain flips a visual scene (goggles experiment).
“Binding Problem”
Images in the brain are left-right reversed and top-bottom reversed. Somehow, it all straightens out and we don’t know how. Hence, the “binding problem.”
How Much of the Brain is Used to See?
HALF!!!
