The oval window of the middle ear is the entry to the vestibular canal within the
fluid-filled and snail-shaped cavity, the cochlea of the inner ear. During sound
activity, the stirrup strikes the membrane of the oval window, creating a travelling
wave within the fluid of the canal. The wave wanders along the full length of the
cochlea and returns via the tympanic canal to a second window, the round window (fenestra
cochlea), where the pressure of the wave equalizes.
Along the way, the wave passes over thousands of hair-like sensors. Like an ocean
wave moves the kelp at the bottom of the sea, the sensors also bend with the motion
and trigger nerve impulses. The auditory nerve transmits the coded impulses to the
brain, where the message is interpreted as a specific sound or noise. Loud noise
can damage the sensors. They may become sluggish, may stick together or may even
break off. Once destroyed, they don’t regenerate and the more sensors become damaged
the worse your hearing loss will be.
Sound doesn’t exclusively travel through air. Sound pressure waves may also reach
the inner ear through vibrations of the bones of your skull. The vibrations are able
to stimulate the sensitive receptors in the cochlea and you may hear some of your
voice, even if both auditory canals are blocked.
I have to mention the three semicircular canals on top of the cochlea. They have
nothing to do with hearing, but help you maintain your balance. Without them you
wouldn’t be able to walk. They function similar to the cochlea whereby a fluid moves
within the canals and bends hair-like receptors. The brain interprets the resultant
impulses and instructs certain muscles to keep you upright, for example.
