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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
Q

phototansduction

A

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
Q

Transduction in rods (6 steps)

A
  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
Q

Duplicity Theory

A

Rods and Cones are two different system s

different functions with different characteristics

28
Q

Fovea Vision

A

Central Vision

29
Q

Convergence

A

the relative number of receptors for each ganglion
Cone: 7:1 (1:1 in fovea)
Rods: up to 125

30
Q

Total rods and cones vs ganglion

A

132 million rods and cones

1 million ganglion cells

31
Q

Disc Shedding

A

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
Q

Rods (sensitivity, acuity, convergence)

A

High convergence
High Sensitivity
Low acuity

33
Q

Cones (Sensitivity, acuity, convergence)

A

Low Convergence
Low Sensitivity
High Acuity

34
Q

Pigment Sensitivity

A

rods are sensitive to green, cones it depends

35
Q

Adaptation of photoreceptors

A

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
Q

How is adaptation of photoreceptors measured

A

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
Q

Promotion of dark adaptation

A
  • Change in pupil size
  • dark adapted eyes have higher conc. of rhodopsin
  • unknown higher level processes (Cognition)
38
Q

Types of Ganglion Cell Receptive Fields

A
  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
Q

How to measure receptive fields of photoreceptors

A
  • 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
Q

Types of ganglion cells

A

Magnocellular
parvocellular
koniocellular

41
Q

Magnocellular

A 
Rods 
10% 
large cell, large receptive fields 
-- low spatial resoluation/ acuity 
low levels of light needed (high sensitivity) 
important in perception of motion
42
Q

Parvocellular

A 
cones 
80% 
small receptive field 
-- high spatial resolution 
require high contract differences 
-- low sensitivity 
- conveys colour information
43
Q

koniocellular

A

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
Q

Visual Pathway Summary

A

optic nerve , optic chiasm, optic tract , superior colliculus, lateral geniculate nucleus, cerebral cortex

45
Q

Optic Chiasm

A

Division of input from each eye
temporal side of each eye: ipsilateral
nasal side of each eye: contralateral

46
Q

Superior Colliculus

A

multisensory integration
involved in localization (WHERE)
dorsal system
magnocellular

47
Q

Lateral Geniculate Nucleus

A 
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
Q

Cerebral Cortex / Visual Cortex

A

Divided into broadmanns areas
Area 17: Primary Visual Cortex
Areas 18.19: secondary visual cortex

additional areas in ventral cortex area

49
Q

Primary Visual Cortex

A

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
Q

Neurons in visual cortex

A

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
Q

Simple Cells

A

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
Q

Complex Cells

A

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
Q

Hypercomplex

A

areas 18 and 19
respond to moving lines or angles of specific size

Specific sizes in specific orientations and moving

54
Q

End Stopped Cells

A

Simple and complex cells that produce larger neural respond in receptive field if they have good fit w/ receptive field

55
Q

Tilt effect

A

orientation specificity, different pieces picked up by each cells (elementarist?)

Survey of the Senses (12 decks)

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