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Mechanisms of hearing

The sound waves as described earlier, travel through the air where they move and collect in the ear by the outer ear, known as pinna. From here the waves travel down the auditory canal to the ear drum (tympanic membrane). The movement of the sound waves cause the ear drum to vibrate which in turn causes the small bones (malleus, incus and stapes, collective name of these bones is ossicles), in the middle ear to also vibrate. The vibrations transfer mechanical energy through the middle ear to the cochlea.

The cochlea is a fluid filled tube wound in the shape of a snail shell. It contains the sensory end organ of hearing- the Organ of Corti. There are 20 to 30 000 thousand sensory hair cells or Organ of Corti connected to the walls of the cochlea, which then move slowly backward and forwards in the fluid filled cochlea space.

The organ of Corti is stimulated causing a nerve impulse to be sent to the brain. This is how the mechanical energy (from the sound waves) is converted to electrical energy which the brain translates and interprets.

sound wave conversion  

Exposure to loud noise over time may damage the hearing capability by continually over stimulating the hairs so that they cannot return to the upright position. Some extremely loud noises for example, gun fire will create a sound pressure wave that instantaneously damages hearing known as acoustic trauma. As the hair cells are essentially nervous tissue once damaged, they cannot be repaired or recover. It is over stimulating on a persistence basis to loud noises in the workplace that causes occupational noise induced hearing loss.