Final answer:
The tympanic membrane, commonly known as the eardrum, is the structure in the outer ear that vibrates to transfer sound to the middle ear.
Step-by-step explanation:
Structure of the Outer Ear Responsible for Vibration
The structure of the outer ear that vibrates back and forth to transfer sound wave vibrations to the middle ear is known as the tympanic membrane, or eardrum. When sound waves reach the ear, they travel through the ear canal to the tympanic membrane. The vibrations of the tympanic membrane are transmitted to the three bones of the middle ear, the ossicles (malleus, incus, and stapes), which then transfer the sound to the oval window of the inner ear.
The amplification of sound by the middle ear is important for the upcoming transduction process in the inner ear. Inside the cochlea, the vibrations create pressure waves in the fluid which stimulate hair cells to convert mechanical waves into electrical signals for the brain to interpret as sound. This sequence from sound wave to nerve impulse constitutes the process of transduction of sound.