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How sensation of sound is produced in human ear?



Hearing, or audition, depends on the presence of sound waves, which travel much more slowly than light waves. Sound waves are changes in pressure generated by vibrating molecules. The physical characteristics of sound waves influence the three psychological features of sound: loudness, pitch, and timbre.

    Loudness depends on the amplitude, or height, of sound waves. The greater the amplitude, the louder the sound perceived. Amplitude is measured in decibels. The absolute threshold of human hearing is defined as 0 decibels. Loudness doubles with every 10-decibel increase in amplitude.
An object produces sound when it vibrates in matter. This could be a solid, such as earth; a liquid, such as water; or a gas, such as air. Most of the time, we hear sounds traveling through the air in our atmosphere.

When something vibrates in the atmosphere, it moves the air particles around it. Those air particles in turn move the air particles around them, carrying the pulse of the vibration through the air.
The ear has three basic parts: the outer ear, the middle ear, and the inner ear.

The visible part of the ear is the pinna, which collects sound waves and passes them along the auditory canal to a membrane called the eardrum. When sound waves hit the eardrum, it vibrates. The eardrum transmits the vibration to three bones, or ossicles, in the middle ear, which are called the hammer, the anvil, and the stirrup. The diagram of the ear shows how they got these names: they actually look like a hammer, an anvil, and a stirrup. In response to the vibration, these ossicles move one after another. Their function is to amplify the sound vibrations.

From the ossicles, vibrations move through a membrane called the oval window to the cochlea of the inner ear. The cochlea is a coiled, fluid-filled tunnel.

Inside the cochlea are receptors called cilia or hair cells that are embedded in the basilar membrane. The basilar membrane runs along the whole length of the coiled cochlea. Vibrations that reach the inner ear cause the fluid in the cochlea to move in waves. These waves in turn make the hair cells move.

The movement triggers impulses in neurons that connect with the hair cells. The axons of these neurons come together to form the auditory nerve, which sends impulses from the ear to the brain. In the brain, the thalamus and the auditory cortex, which is in the temporal lobe of the cerebrum, receive auditory information.


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