What fills the scala tympani of the cochlea?

The correct answer is perilymph. The scala tympani is one of the fluid-filled chambers in the cochlea, which is part of the inner ear. It is located beneath the scala vestibuli and is separated from it by the basilar membrane. Perilymph is a fluid similar in composition to extracellular fluid and is found in the space between the osseous (bony) labrynth and the membranous labyrinth of the cochlea, including the scala tympani.

This fluid plays a crucial role in the auditory process, as sound vibrations cause the perilymph to move, which in turn causes the basilar membrane to vibrate, leading to the stimulation of hair cells in the organ of Corti and the initiation of the auditory signal that is sent to the brain.

In contrast, endolymph fills the scala media, which is the chamber above the scala tympani. Air is not found in the cochlea under normal conditions, as it is a fluid-filled structure, and blood does not fill the cochlear chambers, although blood vessels are present in the surrounding tissues. Understanding the distinct roles and locations of these fluids is essential for comprehending the mechanics of hearing.