The Cochlea

The principle auditory organ of the inner ear is the cochlea, shown in the inner ear diagram of Figure 3. Though spiral in shape, it is easiest to think about the cochlea by imagining it has been ``unrolled.'' When thought of in this way, the cochlea contains three parallel ducts running along its length: the scala vestibuli, the scala media (or cochlear duct), and the scala timpani (see Figure 4). The second of these, the scala media, contains a fluid (called endolymph) that is chemically quite different from that of the other two (called perilymph). The three ducts are separated by two membranes: Reissner's membrane, and the acoustically more significant Basilar Membrane (BM). A diagram of these features is shown in the cross section of Figure 4.

Figure 3: Diagram of the inner ear. The cochlea, with its spiral shape, is the primary auditory organ of the inner ear (re-printed with permission from [2]).

Figure 4: Cross-section of the cochlea (re-printed with permission from [1]).