Which anatomical structure converts sound energy into a chemical-electrical signal that is sent to the brain?

The cochlea is the anatomical structure responsible for converting sound energy into a chemical-electrical signal that is sent to the brain. Located in the inner ear, the cochlea is a spiral-shaped, fluid-filled organ that contains sensory hair cells. When sound waves enter the cochlea, they create fluid vibrations, which cause these hair cells to bend. This bending opens ion channels, leading to the generation of electrical signals. The auditory nerve then carries these signals to the brain for processing, allowing us to perceive sound.

The other structures have important roles in the hearing process but do not perform the conversion of sound energy directly into electrical signals. The tympanic membrane, or eardrum, vibrates in response to sound waves, but it does not transform those vibrations into neural signals. The stapes, the small bone in the middle ear, amplifies these vibrations before they enter the cochlea. The auditory nerve transmits the signals generated by the cochlea to the brain but does not convert sound energy into signals itself.