How the human ear works

The pinna collects sound waves and directs them into the ear canal.
The sound waves impinge on the tympanic membrane and make it vibrate.The vibrating tympanic membrane causes the malleus,incus and stapes to move to and fro.In turn,the stapes pushes the oval window in and out.Since the surface area of the oval window is much smaller than that of the tympanic membrane, the vibrations at the oval window are greatly amplified.
The vibrating oval window causes the perilymph in the cochlea to move to and fro,i.e pressure waves are set up in the perilymph. Since the perilymph is a liquid and cannot be compressed,its movements push the round window out and in. The round window is in contact with the middle ear,so its outward movements simply compress the air in the middle ear, thereby releasing the energy of the pressure waves harmlessly.
The pressure waves in the perilymph push the membrane separating the upper canal and the cochlear duct to and fro.These movements set the endolymph in motion. This in turn,causes the elastic basilar membrane to vibrate,but the more rigid tectorial membrane remains fairly stationary.As a result,the hairs of the sensory cells between these two membranes bend,causing nerve impulses to be sent to the brain via the cochlear part of the auditory nerve.
High pitched sounds make the basilar membrane near the round window vibrate more; low pitched sounds cause the basilar membrane near the tip of the cochlea tube to vibrate more. The brain is thus able to determine the pitch of sound by the regions of the cochlea which send the nervous impulses.


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