What is the cochlea?

• A. A spiral-shaped organ responsible for converting vibrations into neural signals
• B. A flat membrane separating middle and inner ear
• C. A fluid-filled chamber that amplifies sound
• D. A nerve that transmits to the brain

Answer: (A)

The cochlea is the spiral-shaped organ of hearing in the inner ear where mechanical energy from sound is transformed into neural signals. Sound waves set the eardrum and then the tiny bones in the middle ear into motion, which drives fluid waves inside the cochlea through the opening at the oval window. These waves move the basilar membrane, causing hair cell stereocilia to bend. That bending opens ion channels, creating receptor potentials and releasing neurotransmitters to activate the auditory nerve fibers. The auditory nerve then carries the information to the brain, where it’s processed as sound. The cochlea also maps different frequencies along its length (tonotopy), so different pitches stimulate different parts. It’s not a flat membrane separating middle and inner ear, not a fluid-filled chamber that simply amplifies sound, and not the nerve that transmits impulses to the brain.