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38.3 Sense of Vision -- Part 1
The olfactory cells decline with age, and the remaining population becomes less sensitive.
Older people tend to apply excessive amounts of perfume.
As a result of head trauma, respiratory infections, or brain disease, the ability to smell can be lost.
If these individuals can't smell spoiled food, a gas leak or smoke, this condition can become dangerous.
If you have a cold, you may think food has lost its taste, but most likely you have lost the ability to smell it.
This method is also used in reverse.
The taste buds in the mouth are stimulated when you smell something.
It is possible that part of what we refer to as smell is taste.
The senses of smell and taste can be compared and contrasted.
There are five types of taste in humans.
Discuss how the different sense organs would interpret a nerve impulse.
List the tissues and cell layers through which light enters the eye.
Discuss the different roles of rod cells, cone cells, and rhodopsin.
Many, but not all, animals have vision.
Like the senses of smell and hearing, vision allows us to see at a distance, which can have survival value.
In this section, we look at how animals and humans see.
The light is sensitive to the sensory cortex of the brain.
Some animals rely on senses other than smell and hearing, while other animals have the same function.
moles use their senses of smell and touch rather than sight.
Some photoreceptors do not form images.
The planarians have "eyespots" that allow them to sense and move away from light.
The arthropods have many independent visual units.
Each possessed all the elements needed for light reception.
Light rays are directed toward the photoreceptors by the cornea and the crystalline cone.
The brain gets its nerve impulses from the photoreceptors.
Stray light rays are absorbed by the outer pigment cells, so that they don't reach the other.
A compound eye has a lens and a cornea that focus light onto the cells of the brain.
Interpretation produces a mosaic image by sending nerve impulses to the brain.
Research shows that bees use their sense of vision to estimate how far they have traveled from their hive.
Most insects see a limited number of colors compared to humans.
Many insects can see some ultraviolet rays, and this allows them to locate the parts of flowers that have ultraviolet patterns.
Most birds and fishes have color vision, but only humans and other primate have it.
Humans and insects see the same things because their eyes respond to ultraviolet rays.
The reproductive parts of flowers are often highlighted by these types of markings.
This similarity is an example of convergent evolution.
The visual field is focused on by a single lens.
In animals, the lens changes shape to aid focusing, but in molluscs, the lens moves back and forth.
A piece of film in a camera can be compared to the photoreceptors taken together.
The human eye is more complex than a camera.
Animals with two eyes looking in the same direction have three-dimensional vision.
Each eye can see an object from a different angle because of the overlap of the visual fields.
Humans and predator tend to have the same vision.
rabbits have meaning that their visual field is very wide because of their eyes facing sideways.
It is more difficult for a predator to sneak up on an animal with a panoramic vision.
The sclera, choroid, and retina are the three layers of the human eye.
In front of the eye, the sclera becomes the transparent cornea, the window of the eye.
The sclera is the outer layer of the eye and the choroid is the middle layer.
The inner layer of the eye is called the retina.
Vision is most acute in the fovea centralis.
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