Eyes and Vision

Question 1

What are 3 different light sensing organs in insects?

Answer 1

1. compound eye
2. ocellus
3. stemma

Question 2

What are compound eyes used for?

Answer 2

perceive light, movement, complex image formation

- provide wide field of view

Question 3

What are ocelli used for?

Answer 3

very sensitive to changes in light intensity

- probably not used in image formation

Question 4

What are stemmata used for?

Answer 4

minimal image formation

Question 5

What insects use compound eyes?

Answer 5

most adult insects except lice and female scale insects

Question 6

what insects use ocelli?

Answer 6

many adult insects, larvae of hemimetabolous insects

Question 7

what insects use stemma?

Answer 7

holometabolous larvae ( they are the only visual organs used by them)

Question 8

What are ommatidia?

Answer 8

• an aggregate of subunits in the compound eye

- external surface of eye is faceted (hexagonal shaped in insects with large #s of ommatidia)

Question 9

what are the two morphological elements of a compound eye? what do they do?

Answer 9

1. optical part - light gathering part

2. sensory part - transforms light energy into an electrical signal

Question 10

What are the parts of the optical part of the compound eye?

Answer 10

1. cuticular lens

2. crystalline core

Question 11

What is the cuticular lens of the compound eye? what does it do?

Answer 11

clear, colorless lens which is secreted by modified epidermal cells (corneagen cells).
- optimizes transmittance and limits reflectance of incipient light

Question 12

What is the crystalline core of the compound eye?

Answer 12

consists of 4 “semper” cells and made of hard, clear intracellular substance.
- surrounded by primary pigment cells (corneagen cells)

Question 13

What are retinula cells? where are they found and are they part of the optical or sensory part of the compound eye?

Answer 13

a group of elongate primary neurons that transduce stimuli and transmit signals onward

• found behind the cone of the compound eye
• part of the sensory part of the compound eye

Question 14

What are rhabdomeres?

Answer 14

a margin running the length of each retinula cell that contains light sensitive pigments

Question 15

How many retinula cells does each ommatidium have?

Answer 15

6-8 in close contact

Question 16

What is a rhabdom?

Answer 16

a fusion of rhabdomeres into a central light sensitive rod

Question 17

What are rhabdoms surrounded by? how many? why?

Answer 17

12-18 secondary pigment cells that serve to isolate each ommatidium

Question 18

What are rhadopsins?

Answer 18

visual pigments similar to those in vertebrates contained in the rhabdom
- conjugated proteins

Question 19

What is a retinaldehyde?

Answer 19

the chromophore in the rhodopsin proteins

- aldehyde derivative of vitamin A

Question 20

what happens to the chromophore in the presence of light?

Answer 20

it isomerizes from the cis to the trans configuration, producing depolarization of the neural membrane, generating a nerve impulse (Action potential)

Question 21

what kind of insects have a photopic eye?

Answer 21

diurnal insect species

Question 22

what kind of insects have a scotopic eye?

Answer 22

nocturnal/crepuscular insect species

Question 23

What is the structure of the scotopic eye?

Answer 23

there is a long translucent filament connecting the cone to the rhabdom. the filaments are isolated by secondary pigment cells whose pigments can migrate

Question 24

What happens in scotopic eyes in the light?

Answer 24

the pigments occur throughout the cells to isolate the filaments such that the eye functions much like a photopic eye

Question 25

What happens in the scotopic eye in the dark?

Answer 25

the pigments migrate upwards, allowing the filament to receive not only from its own cone (light parallel to the longitudinal axis of the ommatidium). but from the adjacent ommatidium as well.

Question 26

The scotopic eye allows what? (in terms of visualization)

Answer 26

low visual acuity but high light sensitivity

Question 27

What is the apposition type of eye?

Answer 27

the eye received a large number of point images (corresponding to each rhabdom)
- sharpness proportional to the number of ommatidia responding

Question 28

What is the superposition type of eye?

Answer 28

point images at each rhabdom were formed from light rays collected by several adjacent ommatidium

Question 29

What type of eye is and photopic eye and scotopic eye?

Answer 29

photopic: apposition
scotopic: superposition

Question 30

What is the current concept for image formation?

Answer 30

image formed at the rhabdom has no physiological significance per se. there is a large amount of anatomical convergence of rhabdomere neurons in the optic lobes of the brain - cross-fibre patterning may form the image

Question 31

What is the real function of the compound eye?

Answer 31

may be the perception of movement rather than image formation

Question 32

How is movement seen in the compound eye?

Answer 32

as rapid changes in light intensity at any given ommatidium

Question 33

what is the flicker effect?

Answer 33

the number of stimuli per unit time to which the eye is sensitive

Question 34

What does the flicker effect depend on?

Answer 34

the speed of neural recovery from a previous stimulus ( the flicker fusion frequency)

Question 35

What is a ‘fast’ eye? what insects have it?

Answer 35

faster succession of light stimuli produces better image formation via rapid scanning to produce the shape of the object.
- diurnal, fast flying insects have it

Question 36

what insects have ‘slow’ eyes?

Answer 36

nocturnal, slow flying insects

Question 37

What pattern do honeybees perceive form on?

Answer 37

the basis of the brokenness of a pattern

- broken or interrupted patterns may produce a flickering visual impression as a bee passes during flight

Question 38

What are contained within ocelli?

Answer 38

500-1000 retinular cells sharing a common lens; each 2-5 adjacent cells forms a rhabdom

Question 39

What transfers code to the brain in ocelli?

Answer 39

secondary neurons

Question 40

What wavelengths do ocelli respond to?

Answer 40

same wavelengths as compound eyes but much more sensitive to low light levels

Question 41

What depend on ocelli?

Answer 41

• diurnal rhythms
• may influence the insects response to information received from the compound eyes as painting over them inhibits light directed behavior even when compound eyes are functional

Question 42

What do stemma resemble?

Answer 42

single ommatidium

Question 43

What do stemma consist of?

Answer 43

a lens, cornea and rhabdom

Question 44

What are stemma capable of?

Answer 44

most minimal image perception (large areas of dark vs. light)