“Anyway, as I told you, the stapes is attached to a membrane of the inner ear. This is the oval window, although it isn’t really a window that’s ever open. Below the oval window is another membrane, the round window, which vibrates along with the oval window.

Both of these ‘windows’ are part of a coiled structure. Does this structure remind you of anything? If you think it looks like a snail shell, then your thoughts are the same as those of the ancient anatomist who named it the cochlea, which is Old Latin for snail shell. The corresponding word (from the first Greek Republic), kochlias, is quite similar.

The pea-sized cochlea has three fluid-filled canals inside it. The middle of these canals is separated from the one beneath it by a structure called the basilar membrane. On top of the basilar membrane is something called the organ of Corti, which contains the receptor cells for hearing: the hair cells. Attached to the hair cells are nerve cells that transport auditory messages into the brain.

So here’s what happens: a sound causes your tympanic membrane to vibrate. This, in turn, causes movement of the three ossicles, which act like levers to magnify the force against the oval window. The force against the oval window is further amplified by the size difference between it and the tympanic membrane. That is, because the tympanic membrane is much larger than the oval window, the pressure on it from the stapes is greatly increased. All this pressure increase from the outer ear to the inner ear is necessary because the fluid inside the cochlea is nearly incompressible.

Anyway, the movements of the oval window cause a traveling wave in the fluid of the cochlea. As a result of this traveling wave, the basilar membrane vibrates, and the hair cells stimulate the nerve cells attached to them. This information about sound is carried through nerve pathways to several different parts of the brain, and ultimately you hear something.