The scala tympani is one of the three fluid-filled chambers, or scalae, of the cochlea in the inner ear, integral to the process of hearing.
Structure
The scala tympani is located below the scala media (cochlear duct) and is separated from it by the basilar membrane, a critical component in the auditory transduction process. The scala tympani begins at the round window, one of the two openings into the cochlea from the middle ear, and spirals from the base to the apex of the cochlea, paralleling the scala vestibuli and scala media. Like the other scalae, the scala tympani is filled with perilymph, a fluid similar in composition to cerebrospinal fluid, which contrasts with the potassium-rich endolymph filling the scala media.
The walls of the scala tympani are formed by the bony structure of the cochlea, and its inner space is lined with a thin layer of cells that help to maintain the ionic composition of the perilymph. At the apex of the cochlea, the scala tympani meets the scala vestibuli at a small opening called the helicotrema, allowing perilymph to flow between these two chambers.
Function
The scala tympani plays a crucial role in the mechanics of hearing:
- Transmission of Sound Waves: When sound waves enter the cochlea via the oval window, they cause the perilymph in the scala vestibuli to move. This movement generates a wave that travels through the perilymph of the scala vestibuli, crosses the helicotrema, and then propagates back down the cochlea within the scala tympani. The movement of perilymph within the scala tympani induces vibrations in the basilar membrane, activating the hair cells in the organ of Corti located in the scala media above.
- Dissipation of Sound Energy: After stimulating the hair cells, the sound-induced wave in the perilymph dissipates as it travels through the scala tympani towards the round window. This dissipation allows the round window membrane to bulge outward slightly, preventing the build-up of excessive pressure within the inner ear and ensuring that the fluid wave can be effectively transmitted through the cochlea.
The scala tympani’s role in transmitting and dissipating sound-induced pressure waves is essential for the proper functioning of the cochlear mechanism and the conversion of sound waves into neural signals that can be interpreted by the brain. Its structural and functional integrity is vital for hearing and overall auditory health.
