How we hear

Our two ears act like radar antennas to register acoustic signals coming from multiple directions. The complex structures of each ear process the received signals and pass them to the brain where we interpret our acoustic environment. Take for example the sound of an approaching truck: the nearest ear receives the sound slightly earlier than the other and a little louder. Using the finely processed acoustic information from each ear, the brain has the capacity to calculate the direction of the truck's approach and we also "know" approximately how close it is.

Function of the ear
The ear is a very complex organ comprising three parts: the outer ear, the middle ear and the inner ear. From the inner ear the auditory nerve transmits information to the brain for processing.

a) The outer ear
The outer ear includes the auricle, the auditory canal and the eardrum. The auricle helps to gather the sound waves, and the auditory canal then directs them to the eardrum.

b) The middle ear
The middle ear is an air-filled cavity which contains the smallest bones in the human body - the malleus, incus and stapes. These are connected to the eardrum on one side, and on the other side to a thin membrane-covered opening on the wall of the inner ear. The middle ear is also connected to the throat via the Eustachian tube which keeps the air pressure in the middle ear equal to that of the surrounding environment.

c) The inner ear
In the inner ear, the auditory input is processed by the cochlea, while information affecting balance is processed by the semicircular canals. Along the entire length of the fluid filled cochlea, there are tiny hair cells. These hair cells are bent when the fluid is displaced by sound waves passed on by the middle ear bones. This triggers a mechano-electical transduction which activates the corresponding nerve endings. These then transmit the message to the area of the brain in charge of interpreting auditory input.

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