ch. 50 vision

Question 1

what do most invertebrates have

Answer 1

light-detecting organ

Question 2

simplest light-detecting organ

Answer 2

pair of ocelli called eyespots located near the head of planarians

Question 3

what do eyespots of planarians do

Answer 3

allow planarians to move away from light and seek shaded locations (negative phototaxis)

Question 4

what have ommatidia

Answer 4

insects, crustaceans, polychaete worms

Question 5

compounds eyes

Answer 5

consist of several thousand light detectors called ommatidia

Question 6

what are compound eyes effective at

Answer 6

detecting movement

Question 7

color vision of insects

Answer 7

excellent - some can see ultraviolet range

Question 8

where are single-lens eyes found

Answer 8

some jellies and polychaete worms, spiders, and many molluscs, vertebrates

Question 9

how to single-lens eyes work

Answer 9

camera-like principle - iris changes diameter of the pupil to control how much light enters

Question 10

choroid

Answer 10

thin, pigmented layer of the eye

Question 11

what is just inside the choroid

Answer 11

retina with neurons and receptors

Question 12

lens

Answer 12

transparent disk of protein

Question 13

what is in front of the lens

Answer 13

clear and watery aqueous humor

Question 14

what is behind the lens

Answer 14

jellylike vitreous humor

Question 15

path of light through eyeball

Answer 15

• cornea
• aqueous humor
• pupil - controlled by iris constricted/dilating
• lens (living tissue)
• vitreous humor
• retina (photoreceptors, bipolar cells, ganglion cells)
• optic nerve

Question 16

what are the ciliary muscle connected to

Answer 16

the lens by suspensory ligaments - holds lens in place

Question 17

myopia

Answer 17

focused in front of the retina

Question 18

hyperopia

Answer 18

focused behind the retina

Question 19

fovea

Answer 19

center of visual field compact with tons of cones and contains no rods

Question 20

what is most of the retina composed of

Answer 20

rods

Question 21

2 types of photoreceptors in retina

Answer 21

1. rods
2. cones

Question 22

where do the neurons of the retina relay visual information to

Answer 22

the optic nerve and brain

Question 23

optic disk

Answer 23

place in retina where optic nerve attaches to eye, lacks photoreceptors and forms a blind spot

Question 24

rods

Answer 24

more sensitive to light but don’t distinguish colors

Question 25

cones

Answer 25

provide color vision

Question 26

what do vertebrate visual pigments consist of

Answer 26

retinal bound to opsin

Question 27

retinal

Answer 27

light-absorbing pigment

Question 28

opsin

Answer 28

membrane protein

Question 29

ex. of vertebrate visual pigment

Answer 29

rhodopsin

Question 30

what does an absorption of light cause

Answer 30

change of shape in retinal

Question 31

glutamate in light

Answer 31

no glutamate released

Question 32

glutamate in dark

Answer 32

glutamate released as neurotransmitter from rods and cones to neurons called bipolar clues

Question 33

when light hits retinal, what happens to its shape

Answer 33

changes from cis isomer (bent) to trans isomer (straight)

Question 34

signal transduction in eyes

Answer 34

- light changes cis-retinal to trans-retinal - trans-retinal activates rhodopsin - G protein activated - transducin activated - hydrolysis of cyclic GMP to GMP by phosphodiesterase - sodium channels close - cell hyperpolarized and rate of glutamate neurotransmitter release slows

Question 35

what does cGMP do in the dark

Answer 35

bind to sodium ion channels and keeps them open

Question 36

what happens when cGMP breaks down

Answer 36

Na+ channels close - hyper polarizes cell

Question 37

how is the signal transduction pathway usually shut off

Answer 37

enzymes convert retinal back to cis form

Question 38

bleaching

Answer 38

- light strikes cis-retinal and turns it to trans - bleaching occurs - ATP to ADP used by enzyme converts trans back to cis

Question 39

where does the processing of visual information begin

Answer 39

retina

Question 40

what does the decrease in glutamate do

Answer 40

change membrane potential of bipolar cells

Question 41

lateral inhibition

Answer 41

rod/cone stimulates horizontal cell, horizontal cell then habits more distant photoreceptors and bipolar cells - regions receiving light appear lighter, dark surroundings appear darker

Question 42

what does a single ganglion receive information from

Answer 42

array of rods and cone - defines receptive field

Question 43

what does a smaller receptive field typically result in

Answer 43

a sharper image

Question 44

optic chiasm

Answer 44

where optic nerves meet near center of base of cerebral cortex

Question 45

where are sensations from the left visual field of both eyes transmitted

Answer 45

to right side of brain and vise versa

Question 46

what vertebrates have good color vision

Answer 46

fish, amphibians, reptiles, birds

Question 47

what comprises the minority of mammals that can see color well

Answer 47

humans and primates

Question 48

mammals with nocturnal vision

Answer 48

have high proportion of rods in the retina and probably see a pastel world during the day

Question 49

what is the perception of color based off of in humans

Answer 49

3 types of cones

Question 50

3 types of cones

Answer 50

red, green, and blue - different visual pigments (photopsins)

Question 51

when are photopsins formed

Answer 51

when rental binds to 3 distinct opsin proteins

Question 52

what does abnormal color vision result from

Answer 52

mutations in the genes for one or more photopsin proteins

Question 53

what did researchers studying color vision in squirrel monkeys do

Answer 53

make breakthrough in gene therapy - males are red-green color-blind - when researchers introduced missing gene in virus, full color vision apparent

Question 54

focusing

Answer 54

changing shape of the lens

Question 55

near vision/accommodation

Answer 55

- ciliary muscles contract - suspensory ligaments relax lens becomes thicker and rounder

Question 56

distance vision

Answer 56

- ciliary muscles relax - suspensory ligaments pull against lens - lens becomes flatter