Vertebrates 19 - Vision

Question 1

Median eyes

Answer 1

pineal or parietal organs. Not image forming, just sense brightness and the duration of light. Connect to pineal gland

Question 2

Pineal glad

Answer 2

Produces melatonin most when dark. In mammals it reads from the retina instead of pineal eyes.

Question 3

Melatonin

Answer 3

Affects circadian rhythms. Metamorphosis in amphibians, sexual cycles (with change in seasons), skin pigment changes in amphibians

Question 4

Image forming eyes

Answer 4

Real eyes. Durr.

Question 5

Sclera

Answer 5

Outer layer, white part. Holds everything else in.

Question 6

Coroid layer

Answer 6

Blood vessels, pigmented epithelia. Pigment can absorb or reflect light.

Question 7

Tapetum lucidum

Answer 7

Reflective layer in coroid layer made of guanine crystals. Reflects light so it can activate photoreceptors better, but image is a bit less clear. Important for nocturnal animals.

Question 8

Fovea

Answer 8

Highest concentration of photoreceptors

Question 9

Optic disk

Answer 9

Blind spot where optic nerve is. Can see images here.

Question 10

Vitreous humour

Answer 10

Supports lens and retina.

Question 11

Aqueous humour

Answer 11

B/w cornea and lens.

Question 12

Cornea

Answer 12

Allows light to pass through

Question 13

Lens

Answer 13

Focuses light onto the retina.

Question 14

Ciliary body

Answer 14

Affects size/shape of the lens to focus the light.

Question 15

Iris

Answer 15

Control amount of light entering eye through pupil.

Question 16

Pupil shapes

Answer 16

Goats/sheep - horizontal; snakes, cats - vertical

Question 17

Eyelid

Answer 17

Skin for protecting the eye

Question 18

Nictitating membrane

Answer 18

“third eyelid”, covers most of eye. Can be under the eyelid (cat) or without eyelid (shark).

Question 19

Retina

Answer 19

Pigmented layer. Photoreceptors go to bipolar cells to ganglion to nerve. A few other things to integrate info before the brain.

Question 20

Retinal pathway

Answer 20

Optic nerve to the optic chiasm where R and L cross and split. Processed in the visual cortex on the opposite side from eye. Thalamus is relay center to occipital lobe or superior colliculus

Question 21

Superior colliculus

Answer 21

Coordinates motor movements of eyes. Connected to the thalamus.

Question 22

Photoreceptors in the eye

Answer 22

Rods and cones. Have cell bodies to produce proteins etc, and the outer segment which is important in sensing light. Contain second layer of membrane called membrane disks

Question 23

Membrane disks.

Answer 23

In the outer segment. Contain rhodopsins: protein part (opsin) and retinal (Vit A derivative)

Question 24

Rods

Answer 24

high sensitivity, low acuity, 400-600nm

Question 25

Cones

Answer 25

low sensitivity, high acuity (detail). Usually sensitive to only one wavelength.

Question 26

Cone types

Answer 26

Depend on the rhodopsin (specifically the opsin, retinal is same) Blue (450nm), Green (525nm), Red (650nm), some UV (360nm)

Question 27

Tetrachromats

Answer 27

Have 4 cones. Birds and lizards

Question 28

Dichromats

Answer 28

Have 2 cones. Most mammals. Lost 2 rhodopsins to reach this.

Question 29

Trichromats

Answer 29

Have 3 cones. Include primates, humans. Gained a 3rd after ancestor lost 2.

Question 30

Evolution of mammals and vision

Answer 30

First mammals were nocturnal etc. Colour helped gain access to new food etc.

Question 31

Phototransduction in Dark

Answer 31

Increase cGMP, opens Na channel (dark current channel), flow in. Depolarize the cell, release glutamate to transmit signal

Question 32

Phototransduction in Light conditions

Answer 32

Retinal converted from cis to trans, elongates and changes shape of rhodopsin, activates transducin, activates phosphodiesterase, makes cGMP to GMP, Na channel doesn’t stay open, repolarizes membrane.

Question 33

Compare Phototransduction in light and dark

Answer 33

Dark: depolarized, Na open, inactive rhodopsin, glutamate released. Light: Na closed, active rhodopsin, hyperpolarized

Question 34

Terrestrial eyes

Answer 34

Tear glands for moisture, cornea and lens involved in refracting light, thin lens, eyelids (1 or more), some have nictitating membrane, fast pupillary response (more changes), variable number of rods/cones, tapetum lucidum in some

Question 35

Aquatic eyes

Answer 35

No tear glands, Cornea does not refract (water does), lens does, round lens, most have no eyelids, some have nictitating membrane, slow pupillary response (generally constant), mostly rods (less light), tapetum lucidum in some

Question 36

Eyelid

Answer 36

Helps protect the eye as well as help get moisture across the eye.

Question 37

Eyes on side

Answer 37

Little overlap, but greater field behind. Defense in prey species (rabbits, shore birds, chameleons)

Question 38

Binocular vision

Answer 38

Both in front: greater binocular vision, less periphery. Predators: raptors, cheetahs etc

Question 39

Depth perception

Answer 39

Image to one eye is a little larger than the other, brain understands this as a difference in distance.