What causes pressure waves in the fluid of the scala vestibuli and scala tympani?

What causes pressure waves in the fluid of the scala vestibuli and scala tympani?

• A. Movement of the eardrum
• B. The amplified vibration picked up by the oval window
• C. Round window expansion
• D. Basilar membrane vibration

Answer: (B)

Sound waves are turned into mechanical energy by the tympanic membrane and the ossicular chain, and that energy is delivered to the inner ear through the oval window. The stapes pushes on the oval window, and because this boundary is between air in the middle ear and fluid in the cochlea, its inward motion generates pressure changes in the perilymph of the scala vestibuli and scala tympani. These pressure changes propagate as waves through the cochlear fluids and set the basilar membrane into motion. The round window simply bulges outward to allow that fluid movement and not to create the waves. So the pressure waves in the cochlear fluids come from the oval window being driven by the amplified vibration of the eardrum and ossicles.

Sound waves are turned into mechanical energy by the tympanic membrane and the ossicular chain, and that energy is delivered to the inner ear through the oval window. The stapes pushes on the oval window, and because this boundary is between air in the middle ear and fluid in the cochlea, its inward motion generates pressure changes in the perilymph of the scala vestibuli and scala tympani. These pressure changes propagate as waves through the cochlear fluids and set the basilar membrane into motion. The round window simply bulges outward to allow that fluid movement and not to create the waves. So the pressure waves in the cochlear fluids come from the oval window being driven by the amplified vibration of the eardrum and ossicles.