How We Hear
The pinna, or outer ear, gathers and collects sound waves funneling them into the ear canal, which leads to the eardrum.
The eardrum is a thin 3-layer membrane that vibrates from the incoming sound waves and sends the vibrations to the ossicles, the three tiny bones in the middle ear. The ossicles include the malleus, incus, and stapes.
The bones in the middle ear amplify, or increase, the sound and send the vibration to the cochlea or inner ear. The cochlea is a fluid-filled organ with an elastic membrane, called the basilar membrane running down its length.
The incoming sound vibrations cause the fluid inside the cochlea to ripple, and a traveling wave forms along the basilar membrane. Hair cells—sensory cells sitting on top of the membrane—move in response to the incoming sound wave. This motion causes the stereocilia, bristly structures on top of the hair cells, to bump up against an overlying membrane and deflect to one side.
As the stereocilia, move, pore-like channels on their surface open up allowing the sound to be converted to an electrical signal. The auditory nerve carries the signal to the brain, which translates it into sound that we recognize and understand.
Hair cells near the base of the cochlea detect higher-pitched sounds, such as certain speech sounds that add clarity to spoken language (for example: the consonants s, f, th). Those nearer the apex, detect lower-pitched sounds (for example: the vowel sounds o, e, u). Women's and children’s voices tend to be in the higher frequency range where men’s voices tend to be at a lower pitch range.
Loud sounds (over 85 dB) can be damaging to the hair cells of the inner ear which causes permanent hearing loss. Dentists and dental professionals are at risk for noise-induced hearing loss as dental instrumentation has been measured in decibel ranges in excess of 85 dB and up to 100 dB.