7565507
Description
Flashcards by Lara Hiles, updated more than 1 year ago
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Created by Lara Hiles
almost 8 years ago
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| Question | Answer |
| What is the dominant sense for birds? | Vision |
| Birds' eyes are very large relative to body size. What is the importance of this? | Allows for larger image on retina which results in higher resolution and ability to see more detail |
| What are the four special features of the avian eye? | (1) Presence of a sclerotic ring (2) Ability to vary curvature of cornea (3) Nictitating membrane (4) Possession of pecten |
| What is the sclerotic ring? | Bony ossicles that support eye and allows for insertion of muscles that can vary curvature of cornea |
| What does the ability for birds to vary the curvature of the cornea allow for? | Changing nearsightedness and farsightedness |
| What is the nictitating membrane? | Translucent membrane that forms an inner eyelid that protects eye from dust and keeps it moist |
| What is the pecten? | Pigmented, highly vascularized structure projecting from retina near junction of optic nerve that circulates vitreous humour which provides nutrients and removes waste products |
| What is the retina? | Layer at back of eyeball containing light sensitive cells that trigger nerve impulses that pass via optic nerve to brain where a visual image is formed |
| What are three similarities between bird and mammal retinas? | (1) Outer layer consists of pigmented epithelium (2) Middle layer contains sensory cells (rods and cones) that transcribe light into electrical impulses to nerves (3) Inner layer contains connecting neurons and nerve fibres |
| What are three differences between bird and mammal retinas? | (1) Sensory cells are more numerous, smaller, and tightly packed (2) Few blood vessels to obscure image which results in enhanced visual acuity (pecten contains blood vessels in a concentrated area) (3) Resolving power is much greater with more cone cells per unit area and a 1:1 connection of cones to bipolar cells and of bipolar cells to optic neurons -> results in finer resolution |
| What are foveae? | Small pits in retina where cones are densely packed and overlaying connecting neurons are reduced; point of greatest visual acuity |
| What is the function of central foveae? | Functions in monocular vision |
| What is the function of temporal foveae? | Function in binocular vision |
| How many foveae do birds typically have? | Two per eye (4 in total) |
| What is a field of vision? | Entire area that can be seen when eyes are fixed in one position |
| What allows for birds to have a large visual field? | Eyes are placed laterally on head and are highly mobile |
| What trade-off allows for most birds to have a large monocular field of vision? | Narrow binocular vision |
| What allows for birds to have well-developed colour vision? | Abundant cone cells Reason why birds tend to possess colourful feathers (exception is nocturnal birds) |
| What are carotenoid pigments? | Coloured oil drops in cone cells that are derived from food sources |
| What four carotenoid pigments do diurnal birds have? | (1) Red (2) Orange (3) Yellow (4) Green |
| What two carotenoid pigments do nocturnal birds have? | (1) Colourless (2) Pale yellow |
| What results in birds have tetrachromatic colour vision? | Possession of four types of cone cells in eye that are sensitive to different spectra with a 1:1 relationship with visual pigmets |
| What is the purpose of birds being sensitive to ultraviolet light? | Can be used for attracting mates or locating prey |
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