Describe the functional relationship between the scala vestibuli, scala tympani, and the cochlear duct.
The correct answer and explanation is:
The scala vestibuli, scala tympani, and cochlear duct are three important components of the cochlea, located in the inner ear, and each plays a critical role in the process of hearing.
The scala vestibuli and scala tympani are both filled with perilymph, a fluid similar to extracellular fluid, and are located on either side of the cochlear duct. The cochlear duct, also called the scala media, is a separate chamber that contains endolymph, a fluid with a different ionic composition than perilymph. The cochlear duct is the structure that houses the sensory organ for hearing, the organ of Corti.
The scala vestibuli is the uppermost chamber, connected to the oval window of the cochlea. The vibration of sound waves causes movement of the stapes, which transmits mechanical energy to the perilymph of the scala vestibuli. This wave of pressure moves through the scala vestibuli and propagates toward the helicotrema, the point where the scala vestibuli and scala tympani meet at the apex of the cochlea.
The scala tympani, located below the cochlear duct, is also filled with perilymph and extends from the helicotrema to the round window. The wave of pressure traveling from the scala vestibuli through the cochlear duct causes the basilar membrane to move, which in turn stimulates the hair cells of the organ of Corti. The movement of the basilar membrane also results in a compensatory movement in the scala tympani, allowing the energy to dissipate at the round window.
The cochlear duct is where the actual transduction of sound into neural signals occurs. As the basilar membrane moves in response to pressure waves in the perilymph, the hair cells of the organ of Corti bend and generate electrical signals that are sent to the brain via the auditory nerve.
Together, the scala vestibuli, scala tympani, and cochlear duct work in concert to transmit sound waves, convert them into mechanical vibrations, and ultimately generate the electrical signals necessary for hearing.