Good Essay About Ear And Eye

Human perception of sounds is not only performed by an ear as a part of the body. In fact, a person hears through the organ of hearing, which has got complex structure. The ear is only a visible part of it.
Auricle or pinna essentially acts as a funnel through which a person catches vibrations in the air. Coming through the auditory canal, they affect the eardrum – a thin membrane that separates the outer and middle ears.
Then the eardrum vibrations are transmitted to the auditory ossicles and reach the inner ear, the main part of which is an organ called the bony labyrinth. The labyrinth is a cavity crimped like a snail shell and filled with fluid. The inner surface of it is lined with so-called “stereocilia” – hair cells. They capture the oscillations of the liquid and pass them to the auditory nerves.
Through the nerves, impulses reach the auditory center, which is located in the cerebral cortex. Only with its help a human being can recognize these signals. One thing to mention, the inner ear and is closely related with the body balance, with the help of which a person localizes its position in space.
A person perceives sound with a frequency of approximately 20 to 20,000 Hz. For example, speech sounds have a frequency of 150 to 2500 Hz. With aging, the perception threshold of sound decreases and the person hears sounds, the frequency of which comes up to 15,000 Hz. Therefore, the elderly have considerably weakened hearing ability, and they hear not all sounds.
Another question arises: “Why do we have two ears?”. Two ears are needed for a man to determine the direction of the source of sound. The importance of hearing ability in human life is very great. The most important thing – with the help of it people can communicate with each other.
The eye – is an organ of the vision, by which a person perceives the light. In contrast to the sound, there is no need in the air for light for its displacement. Light has one more feature distinguishing principle of hearing from seeing: the light is transmitted in a straight line.
The principle of seeing is the following. Through the pupil – a small aperture in front of the eyeball – light beam passes inside. Special structure – crystalline lens – creates an image on the back of the eyeball.
The rear side of the inner eyeball that is opposite to the pupil – fundus – is “paved” with light-sensitive cells. There are two kinds of them: rod cells and cone cells (to distinguish the brightness of light only), and cone cells (for color distinguishing). These cells act like a photocell or camera. They convert light into nerve impulses. By means of the optic nerves, these impulses reach the visual center – a special area of the cerebral cortex where the image is reconstructed. And only with the help of brain activity we can understand the meaning of a particular image that has arisen before our eyes.
However, why do people and all animals have not one, but two eyes? Thanks to availability of two eyes a person can not only recognize objects, but is also able to see spatial relationships between the objects viewed. This feature is called binocular vision.