The cochlea is the portion of the inner ear that looks remarkably like a snail shell. The cochlea is divided into three different chambers, each of which is receptive to different frequencies of sound. The cochlea contains a fluid called perilymph and tiny, sensitive, hair-like projections called cilia.
The cochlea receives sound in the form of vibrations, which cause the perilymph and cilia to move. The cilia then convert these vibrations into nerve impulses that are interpreted by the brain as sound. It may help to think of the cochlea as a microphone.
Jarvis, C. (2004). Ears. In Physical Examination & Health Assessment (341-370). St. Louis, Missouri:Saunders.
The Cochlea of the Inner Ear. Accessed: October 26, 2009 from http://hyperphysics.phy-astr.gsu.edu/hbasees/Sound/cochlea.html#c1