Hearing Of Sound: We can hear sound by our ear which is a very delicate organ of our body. It has three parts.
(i) Outer ear (ii) middle ear (iii) inner ear
The horn-like part of the ear which can be seen from outside is called the outer ear. Near its centre there is an open canal which terminates at a diaphragm called the eardrum. The external ear collects the sound waves and directs them to the eardrum. When the sound waves reach the eardrum, they make it to vibrate. The eardrum separates the outer ear from the middle ear. The middle ear is a small, irregular cavity.
The wall of the middle ear opposite the eardrum, which separates the middle ear from the inner ear, has a small opening called the oval window. Stretching across the middle ear, from the eardrum to the oval window there are three tiny movable bones which are named as hammer, anvil and stirrup. When the sound waves reach the eardrum, it starts vibrating. The feeble vibrations of the eardrum are conveyed to the inner ear through the chain of these bones and the oval window.
The structure of the inner ear is quite complicated but its part which plays an important role in the hearing process is called cochlea. It is shaped like a small snail and filled with a jelly-like fluid. There are countless hair-like structures in cochlea which are the brain. The vibrations produced by the sound waves reach the inner ear through the oval window and the pressure of the liquid in it changes accordingly.
Add the hair-like parts in the cochlea respond to different frequencies of vibrations, they stimulate the different fibres of the auditory nerve which enters into the cochlea from the brain and start sending impulses to the brain where these messages are interpreted as the feeling of sound.