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Survey of the Senses > 2.6 The Visual System > Flashcards

2.6 The Visual System Flashcards

1
Q

The Visual Stimulus

A

Light (electromagnetic Radiation)

Wavelength: distance light travels / cycle
Hue (nanometer)
Amplitude: Height of light wave
brightness candles/m^2
Purity (amount of achromatic light contained in stim)
saturation (colour vision)

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2
Q

Sclera

A

White external membrane of eye

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3
Q

Cornea

A

clear membrane that joins sclera and bulges out.

involved in the focusing of light onto rear surface of eyeball

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4
Q

Astigmatism

A

misshaped cornea results in blurring of some light

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5
Q

Aqueous Humour

A

Waterly liquid (similar to cerebrospinal fluid) that fills anterior chamber

is constantly recycled

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6
Q

Glaucoma

A

increase of pressure in anterior chamber that produces damage to cells at the back of the eye

can be cause when aqueous humour canal for recycling is blocked

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7
Q

Scotopic

A

Dim light conditions

have to get maximal light

Rods

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8
Q

Photopic

A

Bright conditions

have to get optimal energy

Cones

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9
Q

Iris

A

ring of pigmented muscles around eye

mechanism for adjusting light allowed to enter pupil

closed: photopic
open: scotopic

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10
Q

Pupil

A

hole in middle of iris

where light passes through

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11
Q

Lens

A

Changes shape to bring light waves focused on the back of the eye

it accomodations: focus light ways from both nearby and faraway objects

when lens is round (thicker): object is near
- muscles are contracting
when lens is flat (thinner) object is far
- muscles are relaxed

Muscles: zonules and ciliary muscles

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12
Q

cataract

A

when cloudy leans due to injury or disease

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13
Q

retina

A

layer of photoreceptors and nerve cells at rear of eye

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14
Q

optic disk

A

region of retina where optic nerve leaves the eye

No photoreceptors = blind spot

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15
Q

fovea

A

area that produces clearest vision

Macula = direct vision

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16
Q

order of cells that get light in retina

A

light -> ganglion cells (amacrine cells) -> bipolar cells (amacrine cells)-> cones and rods (horizontal cells) -> back of eye

goes through all layers, hits the cone and rods, then works backwards to ganglion cells

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17
Q

Optic Nerve

A

axons of ganglion cells take information out of eye to rest of visual system

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18
Q

Horizontal Cells

A

communication between photoreceptors (cones and rods)

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19
Q

Amacrine Cells

A

communication between ganglion and bipolar cells

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20
Q

@ Fovea (Cell layers)

A

thinner
larger photoreceptors
allows more light to pass through all the layers

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21
Q

Transduction of light

A

happens in photoreceptors

transforming light into neural impulses

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22
Q

Structure of photoreceptors

A 
Cones and Rods 
Outer Segment (where stored/used photopigment) like a stack, the top one is oldest and the one that is used

inner segment (where photopigment is produced) and goes to bottom of outer segment

synaptic terminal where it continues off to bipolar cells

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23
Q

components of photopigment

A

opsin (varies) example: rhodopsin in rods

retinal (vitamin a derivative)

24
Q

4 types of photopigments

A

each one absorbs more light in portion of light spectrum than in any other portion

25
phototansduction
light is first registered by light sensitive molecules in the photoreceptors when photon is absorbed by molecule of rhodospin, it changes the chemical state of photopigment this leads to retinal molecule splitting from opsin (isomerization of the photopigment) isomerization sets off chain reaction that leads to electrical current flowing across the membrane the isomerization means it is no longer the same chemical it has undergone CHEMICAL BLEACHING chemical bleaching leads to changes in electric current in exposure to light
26
Transduction in rods (6 steps)
1. light hits photoreceptor 2. Molecule becomes unstable after absorption 3. retinal and opsin separate 4. retina isomerizes (transformed) 5. transmitter released and blocks Na channels 6. Hyperpolarizes cell (signal that light has hit)
27
Duplicity Theory
Rods and Cones are two different system s different functions with different characteristics
28
Fovea Vision
Central Vision
29
Convergence
the relative number of receptors for each ganglion Cone: 7:1 (1:1 in fovea) Rods: up to 125
30
Total rods and cones vs ganglion
132 million rods and cones | 1 million ganglion cells
31
Disc Shedding
regeneration of photoreceptor (new layer of photopigment on top) cones - at night (dont need it at night) rods - in morning (dont need it during daylight)
32
Rods (sensitivity, acuity, convergence)
High convergence High Sensitivity Low acuity
33
Cones (Sensitivity, acuity, convergence)
Low Convergence Low Sensitivity High Acuity
34
Pigment Sensitivity
rods are sensitive to green, cones it depends
35
Adaptation of photoreceptors
change in sensitivity after exposure to stimular of particular sensitivity dark adaptation: increase in sensitivity as eyes remain in dark light adaptation: decrease in sensitivity as eyes remain in light
36
How is adaptation of photoreceptors measured
Present adaptation stimulus (dark) Present spot of light measure detections threshold for test -- through ascending trials to minimize light adaptation Red Light: Cones adapt in 5 min (High threshold) Green Light: Rods adapt in 30 min (Low threshold)
37
Promotion of dark adaptation
- Change in pupil size - dark adapted eyes have higher conc. of rhodopsin - unknown higher level processes (Cognition)
38
Types of Ganglion Cell Receptive Fields
1. On center - Off Surround 2. Off Center - On Surround Activation is based on retina activation through light stimulus (+) : excitatory connection (on ) (-): inhibitory connection (off) example of this: human grid illusion (inhibitory effect)
39
How to measure receptive fields of photoreceptors
- Used animals and electrode in exact location of visual system (cats or fish) - stereotaxis instument (single cell recording) - - use fish to measure ganglion cells (easy to find) - - use cats to measure higher up in system trial and error by moving light until cell chosen lights up electrode (measures activity through oscilloscope) * size location and direction of movement all important
40
Types of ganglion cells
Magnocellular parvocellular koniocellular
41
Magnocellular
``` Rods 10% large cell, large receptive fields -- low spatial resoluation/ acuity low levels of light needed (high sensitivity) important in perception of motion ```
42
Parvocellular
``` cones 80% small receptive field -- high spatial resolution require high contract differences -- low sensitivity - conveys colour information ```
43
koniocellular
10% of cells smallest cell (as small as dust) colour sensitive (blue center/yellow surround) blinking and eye movement (muscular connection to visual system)
44
Visual Pathway Summary
optic nerve , optic chiasm, optic tract , superior colliculus, lateral geniculate nucleus, cerebral cortex
45
Optic Chiasm
Division of input from each eye temporal side of each eye: ipsilateral nasal side of each eye: contralateral
46
Superior Colliculus
multisensory integration involved in localization (WHERE) dorsal system magnocellular
47
Lateral Geniculate Nucleus
``` detailed analysis of visual stimulus involved in identification (WHAT) ventral system 5 layers: 1,2: magnocellular (localization) 3,4,5: parvocellular (ID) ``` it is topographically mapped - preserves location information
48
Cerebral Cortex / Visual Cortex
Divided into broadmanns areas Area 17: Primary Visual Cortex Areas 18.19: secondary visual cortex additional areas in ventral cortex area
49
Primary Visual Cortex
Area 17 "Striate Cortex" (Strips) thought to be six layers but actually more example: 4C is retinotopic (map of retina) --- this is the information from LGN
50
Neurons in visual cortex
Discovered by Hubel and Weisel using single cell recording of encoding visual information different cell types with different respective fields and response patterns Simple Complex Hypercomplex
51
Simple Cells
respond better to lines and edges in specific orientations and regions in visual field - occular preference for one eye - in layer 4B of area 17 and recieves information from 4C\ lines in specific orientation
52
Complex Cells
layers 2,3, 5 and 6 responds to movement in a specific direction and orientation larger receptive field than simple \ moving lines in specific orientation
53
Hypercomplex
areas 18 and 19 respond to moving lines or angles of specific size Specific sizes in specific orientations and moving
54
End Stopped Cells
Simple and complex cells that produce larger neural respond in receptive field if they have good fit w/ receptive field
55
Tilt effect
orientation specificity, different pieces picked up by each cells (elementarist?)

Survey of the Senses (12 decks)

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