Basic Anatomy and Physiology of the Visual System Flashcards
1
Q
laminar organization of the retina
A
- photo receptors
- rods and cones
- horizontal
- bipolar
- amacrine
- ganglion cells
2
Q
layers of the retina
A
3
Q
Retinal output to __________
A
CNS
4
Q
how do photo receptors in the retina work?
A
- Hyperpolarize when stimulated by light
- Depolarize when exposed to dark or shadow
- Release neurotransmitter (glutamate) when DEPOLARIZED (i.e., exposed to dark such as shadow)
- COUNTER INTUITIVE: Photo Receptors release more glutamate by dark than by light
5
Q
regional differences in retinal structure
A
Periphery of Retina:
- Higher ratio of rods to cones
- Higher ratio of photoreceptors to ganglion cells
- More sensitive to light
6
Q
When center receptors are depolarized (dark) the Bipolar Cell is __________ via horizontal cell connections.
A
hyperpolarized
7
Q
Photo Receptors, Horizontal Cells and Bipolar Cells:
The Big Picture
A
8
Q
what are ganglion cells?
A
- Ganglion Cells Receive input from Bipolar cells
- Connected laterally by Amacrine cells (similar to horizontal cells)
- Ganglion Cells have a similar Center-Surround organization as Bipolar Cells
- On-Center Off-surround or Off-Center On-surround
- Uniform illumination: surround cancels out signal from center and averages out signal
- Ganglion Cells are Responsive to differences in illumination at EDGES
9
Q
__________ is only electromagnetic radiation that we can see.
A
- Wavelength/frequency, amplitude
- Hot colors: Orange, red
- Cool colors: blue, violet
10
Q
Color is constructed in the __________.
A
mind
11
Q
Do rods or cones see color?
A
cones
- Color is perceived through mixing of signals from 3 cone types: blue, green, and red cones
- Each type has a special spectral sensitivity
- Young-Helmholtz trichromacy theory of color vision
12
Q
how do we see all the colors?
A
Opponent Process Theory of Color Vision was developed to account for G-R B-Y oppositions
13
Q
how do color opponent ganglion cells work?
A
[AFTER EFFECT: When one color is saturated the surround opposition color is activated and leads to perception of the opposite color]
14
Q
three types of LGN cells
A
- P-type X ganglion cells (parvocellular [small])
- M-type Y ganglion cells (magnocellular [big])
- W ganglion cells (koniocellular [tiny])
15
Q
P-type ganglion cells
A
- Parvocellular = “small”
- Form & color
- Narrow band
- Selective response to wavelength and fine detail
- Sustained response
16
Q
M-type Y ganglion cells
A
- Magnocellular = “big”
- Gross features & movement
- Broad band: Optimal response to large objects and rapid changes in stimulus
- Transient response
17
Q
W ganglion cells
A
- Koniocellular = “dust/tiny”
- Color
- Visual Attention
18
Q
retinofugal projection
A
19
Q
Visual Pathways - Lateral Geniculate Nucleus
(parts of the brain)
A
- Primary projections to the Lateral Geniculate Nucleus (LGN) in the Thalamus prior to visual cortex
- geniculate = “elbow”
20
Q
Visual Pathways - Lateral Geniculate Nucleus
(visual field)
A
21
Q
non-thalamic targets of the optic tract
A
- Hypothalamus: Biological rhythms, including sleep and wakefulness
- Pretectum: Determines pupil size; certain types of eye movement
- Superior Colliculus: Orients the eyes in response to new stimuli
22
Q
possible problems in
primary area of the visual cortex
(unimodal)
A
- Cortical blindness
- Anton’s syndrome (denial of blindness)
- Blindsight (unconscious perception)
- Anopia Hemianopia (visual field deficit)
- Scotomas
23
Q
possible problems in
secondary area of the visual cortex
(unimodal)
A
- Visual agnosias
- Object agnosia
- Apperceptive: Disruption of basic processes; cannot discriminate or copy simple forms, such as a square or triangle
- Associative: Can perceive and copy an object, but cannot discern meaning (what is it?)
- Integrative: Similar to associative but difficult with details & wholes
- Prosopagnosia
- Color agnosia (achromatopsia)
- Object agnosia
- Akinetopsia– deficit in motion processing
- Dorsal simultaneous agnosia: Can copy objects in a piecemeal fashion but cannot integrate parts of objects into a whole, especially with many parts\
- Optic ataxia: Deficit in visually-guided reaching
- Ocular apraxia: Cannot shift gaze at will with shifts of attention
24
Q
possible problems in
tertiary area of visual cortex
(multimodal)
A
- Object anomia; color anomia
- Alexia (word blindness)
- Disruption of body orientation in extrapersonal space based on visual cues
- Constructional apraxia (based on visual cues) & dressing apraxia
- Disruption of geographic knowledge including environmental agnosia
25
retinotopic and columnar organization of
V1 (striate cortex) BA 17
* Retinotopic organization
* Cellular layers: Wide layer IV, receptive layer
* Columnar organization
* Layer IV - simple cells (location & orientation)
* Complex cells (orientation & movement)
* Hypercomplex (orientation & movement plus other features e.g. width)
* Ocular dominance columns
* Blobs (color) & interblobs (orientation)
26
form perception in the visual cortex
* How does the visual system take an array of varying luminence levels of light impinging on the retina and create representations of objects in space?
* The Gestalt problem of figure-ground
* Hubel & Weisel discovered simple and complex cells in visual cortex for detecting lines, orientations and motion
27
Orientation Sensitivity of Simple Cells in V1
28
Movement / Directional Sensitivity of Complex Cells in V1
29
Visual Cortext Cytochrome Oxidase Blobs
* Blobs cut across ocular dominance columns
* Believed to carry color information
* Recently discovered
30
secondary visual areas of cortex:
dorsal vs. ventral streams
* Ventral stream (“what system”): Color, objects, & faces
* Dorsal stream (“where system”): Spatial orientation, location, object motion, exproprioception (navigation)
31
Secondary visual areas of cortex:
Unimodal Association Areas
Note the Middle Temporal Cortex (MT):
* Involved in motion processing (dorsal stream) yet shows up in ventral stream in some diagrams
* Problem is that MT is not well defined anatomically and differs between species
* Considered part of Dorsal Stream, but not so dorsal!
32
Tertiary visual areas of cortex:
Multimodal/Crossmodal Association Areas
* Angular Gyrus (reading)
* Supramaginal Gyrus (integration of somatosensory auditory and visual info); project into language areas
33
damage of Primary Projection Area:
cortical blindness
* Anton's syndrome (denial of blindness)
* Blindsight (unconscious perception)
* Anopia Hemianopia (visual field deficit)
* Scotomas
34
damage of Secondary Association Areas (Dorsal Stream)
* Middle Temporal Cortex (V5) & adjacent areas: Akinetopsia-- deficit in motion processing
* Dorsal simultaneous agnosia: Can copy objects in a piecemeal fashion but cannot integrate parts of objects into a whole, especially with many parts
* Optic ataxia: Deficit in visually-guided reaching
* Ocular apraxia: Cannot shift gaze at will with shifts of attention
35
damage of Secondary Association Areas (Ventral Stream)
* Visual agnosias
* Object agnosia
* Apperceptive: Disruption of basic processes; cannot discriminate or copy simple forms, such as, a square or triangle
* Associative: Can perceive and copy an object, but cannot discern meaning (what is it?)
* Integrative: Similar to associative but difficult with details & wholes
* Prosopagnosia
* Color agnosia (achromatopsia)
36
damage of Tertiary visual areas of cortex
* Object anomia; color anomia
* Alexia (word blindness)
* Disruption of body orientation in extrapersonal space based on visual cues
* Constructional apraxia (based on visual cues) & dressing apraxia
* Disruption of geographic knowledge including environmental agnosia
