Final answer:
The tympanic membrane is vibrated by sound waves that travel down the auditory canal, causing subsequent vibrations in the ossicles, the oval window, and the fluid within the cochlea, leading to stimulation of hair cells in the basilar membrane.
Step-by-step explanation:
When air molecules set in motion by sound waves travel down the auditory canal, they strike the tympanic membrane, causing it to vibrate. This vibration is transmitted through the malleus, incus, and stapes — the three small bones in the middle ear. The stapes in turn presses into the oval window of the cochlea, setting off a cascade of events that enable us to hear.
The pressurized fluid in the cochlea moves in response to the stapes pressing into the oval window. As pressure waves develop within the fluid, they bend the membrane of the cochlear duct, particularly at points that correspond to the frequencies of the vibrating air molecules. Consequently, hair cells in the basilar membrane are stimulated, which vibrate and translate these mechanical movements into electrical signals that travel along the cochlear nerve to the brain, allowing us to perceive sound.