martes, 5 de abril de 2011

Ear: Hearing and Balance

The senses of hearing and balance are located in your ears
Hearing is the sense of sound perception that results from the movement of tiny hair fibers in the inner ear. These hairs detect the motion of a membrane which vibrates in response to changes in air pressure. Audible sound is sensed by the ear.
Balance sense is the sense which allows an organism to sense body movement, direction, and acceleration, and to attain and maintain postural equilibrium and balance.
Ear structure:
Outer ear: Pinna and ear canal.
The outer ear collects sounds from the environment and funnels them through the auditory system.
The folds of cartilage surrounding the outer ear canal are called the pinna. Sound waves are gathered by the pinna, and funnelled into the ear canal. The sound waves are guided down your ear canal towards the eardrum. The eardrum or tympanic membrane resembles a flexible window that vibrates as sound waves bounce on it
Middle ear: Eardrum and the ear bones (hammer, anvil and stirrup).
The middle ear transmits sound from the outer ear to the inner ear.
This is a hollow, air-filled space also known as the tympanic cavity. It connects to the back of the throat and nose through the Eustachian tubes .
Eardrum vibrations continue into the middle ear. Vibrations travel across the air-filled middle ear cavity through the ear ossicles, a group of three tiny, delicate bones: Hammer, anvil and stirrup. They amplify the eardrum vibrations and transfer to another membrane called the oval window. The oval window separates the middle ear from the inner ear.
Inner ear: Semicircular canals the vestibule and the coclea
The inner ear is responsible for interpreting and transmitting sound sensations and balance sensations to the brain.
This is found in the temporal bone of the head.
The cochlea is responsible for hearing. It is filled with a watery liquid, which moves in response to the vibrations coming from the middle ear through the oval window. As the fluid moves, thousands of mechanoreceptors called hair cells bend and produce nerve impulses towards the temporal lobe of the cerebral cortex.
A very strong movement of the fluid within the cochlea, caused by very loud noise, can kill hair cells. This is a common cause of partial hearing loss and is the reason why users of firearms or heavy machinery should wear earmuffs or earplugs. Destruction of the hair cells usually leads to permanent hearing loss because once destroyed, the hairs do not generally grow back.
The vestibule and 3 semicircular canals are responsible for balance. The canals are arranged at right angles to each other. If you change the position of your head, the fluid in the canals moves. In each canal there is hair cells that sense the strength and direction of the fluid’s movement and send electrical signals to the cerebellum.
When the sense of balance is interrupted it causes dizziness and nausea. Balance can be upset by an inner ear infection, a bad head cold or a sinus infection, or a number of other medical conditions. It can also be temporarily disturbed by rapid and repetitive movement, for example riding on a merry-go-round or spinning around in a circle.
This two videos are aboaut the ear and sound. I think they can help you with your learning.

This last one is about the sense of balance:

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