Flashcards in Vertebrates 19 - Vision Deck (39)
pineal or parietal organs. Not image forming, just sense brightness and the duration of light. Connect to pineal gland
Produces melatonin most when dark. In mammals it reads from the retina instead of pineal eyes.
Affects circadian rhythms. Metamorphosis in amphibians, sexual cycles (with change in seasons), skin pigment changes in amphibians
Image forming eyes
Real eyes. Durr.
Outer layer, white part. Holds everything else in.
Blood vessels, pigmented epithelia. Pigment can absorb or reflect light.
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.
Highest concentration of photoreceptors
Blind spot where optic nerve is. Can see images here.
Supports lens and retina.
B/w cornea and lens.
Allows light to pass through
Focuses light onto the retina.
Affects size/shape of the lens to focus the light.
Control amount of light entering eye through pupil.
Goats/sheep - horizontal; snakes, cats - vertical
Skin for protecting the eye
“third eyelid”, covers most of eye. Can be under the eyelid (cat) or without eyelid (shark).
Pigmented layer. Photoreceptors go to bipolar cells to ganglion to nerve. A few other things to integrate info before the brain.
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
Coordinates motor movements of eyes. Connected to the thalamus.
Photoreceptors in the eye
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
In the outer segment. Contain rhodopsins: protein part (opsin) and retinal (Vit A derivative)
high sensitivity, low acuity, 400-600nm
low sensitivity, high acuity (detail). Usually sensitive to only one wavelength.
Depend on the rhodopsin (specifically the opsin, retinal is same) Blue (450nm), Green (525nm), Red (650nm), some UV (360nm)
Have 4 cones. Birds and lizards
Have 2 cones. Most mammals. Lost 2 rhodopsins to reach this.
Have 3 cones. Include primates, humans. Gained a 3rd after ancestor lost 2.