Chapter 3

Question 1

Light:

Answer 1

form of electromagnetic radiation that travels as a wave

Question 2

Properties of Light

Answer 2

Amplitude: perception of brightness
Wavelength: perception of colour
Purity: mix of wavelengths; perception of saturation

Question 3

Light enters through the _____ then passes through the ____

Answer 3

cornea, lens

Question 4

Lens is capable of adjustments – called

Answer 4

accommodations
When you focus on a close object the lens of your eye gets fatter (rounder) to give you a clear image
When you focus on distant objects, the lens flattens out to give you a better image of objects

Question 5

Retina:

Answer 5

absorbs light, processes images, and sends information to the brain

Question 6

Fovea:

Answer 6

middle point at the back of our light, high concentration of our cones-most refinement

Question 7

Optic disk:

Answer 7

where the optic nerve leaves the eye/blind spot

Question 8

Receptor cells

Answer 8

Rods, cones

Question 9

Rods:

Answer 9

black and white/low light vision
Communicate information about movement, bright or dark

Question 10

Cones:

Answer 10

colour and daylight vision
Communicate information about detail

Question 11

Adaptation:

Answer 11

becoming more or less sensitive to light as needed

Question 12

Distribution on retina

Answer 12

Fovea consists solely of cones
Peripheral retina has both rods and cones
More rods than cones in periphery (outside of the fovea)

Question 13

Blind spot:

Answer 13

place where optic nerve leaves the eye

Question 14

blind spot-We don’t see it because:

Answer 14

One eye covers the blind spot of the other
It is located at edge of the visual field
The brain “fills in” the spot

Question 15

Cornea is ___, but accounts for ___

Answer 15

fixed, ~80% of focusing

Question 16

Lens makes _____ and accounts for the remaining __

Answer 16

accommodations, 20%

Ciliary muscles tighten, lens thickens
Light rays pass through the lens more sharply and focus near objects on the retina

Question 17

Near point:

Answer 17

lens can’t adjust for too close objects

Question 18

Inability to Focus

Answer 18

1- Presbyopia
2- Myopia
3-Hyperopia

Question 19

Presbyopia: “old eye”

Answer 19

Distance of near point increases
Due to hardening of lens and weakening of ciliary muscles (muscles can’t focus enough to see things close)
Corrective lenses are needed for close activities, such as reading

Question 20

Myopia:

Answer 20

“nearsightedness;” inability to see distant objects clearly
Image is focused in front of retina

Question 21

Myopia Caused by:

Answer 21

Refractive myopia: cornea or lens bends too much light
Axial myopia: eyeball is too long

Question 22

Hyperopia:

Answer 22

“farsightedness;” inability to see nearby objects clearly (eye is short)
Image is focused behind the retina
Usually caused by an eyeball that is too short
Constant accommodation for nearby objects can lead to eyestrain and headaches

Question 23

Receptors have outer segments, which contain:

Answer 23

Visual pigment molecules

Question 24

Visual pigment molecules have two components:

Answer 24

Opsin: a large protein
Retinal: a light sensitive molecule

Question 25

Visual transduction occurs when the retinal____

Answer 25

absorbs one photon
Retinal changes its shape (isomerization)

Question 26

Dark adaption:

Answer 26

process of increasing sensitivity in the dark
Measured by determining a dark adaptation curve

Question 27

Visual Pigment Regeneration 1

Answer 27

Light causes the retinal part of the visual pigment molecule to change its shape (A → B)
Leads to separation of retinal and opsin (C)
Visual pigment bleaching (changes in color)

Question 28

Visual Pigment Regeneration 2

Answer 28

Bleached pigments are unable to react to light
process of reforming the visual pigment molecule by re-attaching the retinal
In normal light levels, both bleached and intact visual pigments present (balance)
In low light levels, more intact visual pigments than bleached leads to increased sensitivity

Question 29

Cone vs Rod Regeneration

Answer 29

William Rushton measured regeneration of visual pigment in humans using darkening of retina associated with dark adaptation
Cone pigment regenerates in ~ 6 min
Rod pigment regenerates in 30+ min
Rates match dark adaptation for cones and rods

Question 30

Spectral Sensitivity

Answer 30

Sensitivity of rods and cones to different parts of the visual spectrum
Use monochromatic light to determine threshold at different wavelengths
Threshold for light is lowest in the middle of the spectrum
1/threshold = sensitivity
Produces the spectral sensitivity curve

Question 31

Rod spectral sensitivity

Answer 31

More sensitive to short-wavelength light
Most sensitivity at 500 nm

Question 32

Cone spectral sensitivity

Answer 32

Most sensitivity at 560 nm

Question 33

Purkinje shift:

Answer 33

enhanced sensitivity to short wavelengths during dark adaptation when the shift from cone to rod vision occurs

Question 34

Difference in spectral sensitivity is due to absorption spectra of visual pigments

Answer 34

Rod pigment absorbs best at 500 nm
Cone pigments absorb best at 419nm, 531nm, and 558nm
Absorption of all cones equals the peak of 560nm in the spectral sensitivity curve

Question 35

Difference in spectral sensitivity is due to absorption spectra of visual pigments

Answer 35

Rod pigment absorbs best at 500 nm
Cone pigments absorb best at 419nm, 531nm, and 558nm
Absorption of all cones equals the peak of 560nm in the spectral sensitivity curve

Question 36

1-Rods and cones send signals ____ through:

2-Signals are sent ___:

Answer 36

1) vertically
Bipolar cells
Ganglion cells
Ganglion axons

2) horizontally,
Between receptors by horizontal cells
Between bipolar and between ganglion cells by amacrine cells

Question 37

1-Rods and cones send signals ____ through:

2-Signals are sent ___:

Answer 37

1) vertically
Bipolar cells
Ganglion cells
Ganglion axons

2) horizontally,
Between receptors by horizontal cells
Between bipolar and between ganglion cells by amacrine cells