The cochlea’s two outer chambers are one continuous tube connected at the apex

Evidence

The basilar membrane divides the spiral cochlear tube. It is the seat of all the delicate hair cells, which are clearly key to the transduction of sound into nerve impulses. Any cross section of the cochlea shows three chambers, but the largest two, the scala vestibuli above and the scala tympani below, are actually the same chamber, connected at the apex of the spiral. The basilar membrane separates the scala tympani from the middle chamber, the cochlear duct, or scala media. Pressure started at the oval window by the stapes is transmitted through the scala vestibuli around the apex and back down the scala tympani to the round window, at the end of the scala tympani. The cochlear duct is filled with a different, more potassium-rich fluid than the scala vestibuli above and scala tympani below. — Eric J. Heller, Why You Hear What You Hear- An…, 1947

Categorization

• DEFINE: Distinguishes scala vestibuli and scala tympani as one continuous chamber — a structural key for how pressure waves loop through the cochlea.