The cochlea coils 2.75 turns into three fluid-filled chambers

Evidence

The cochlea consists of a tube coiled into a spiral with approximately 2.75 turns— see Figure 2.3(a). The end with the oval and round windows is the “base,” and the other end is the “apex”—see Figure 2.3(b). Figure 2.3(c) illustrates the effect of slicing through the spiral vertically, and it can be seen in 2.3(d) that the tube is divided into three sections by Reissner’s membrane and the basilar membrane. The outer channels—the scala vestibuli (V) and scala tympani (T)—are filled with an incompressible fluid known as perilymph, and the inner channel is the scala media (M). The scala vestibuli terminates at the oval window and the scala tympani at the round window. An idealized unrolled cochlea is shown in Figure 2.3(b). There is a small hole at the apex known as the “helicotrema” through which the perilymph fluid can flow. — David M. Howard, Jamie Angus, Acoustics and Psychoacoustics, 544

Categorization

• DEFINE: Lays out the standard anatomical vocabulary of the cochlea: base, apex, scala vestibuli, scala tympani, scala media, perilymph, helicotrema.