Summary
Highlights
Auditory transduction is the process by which the ear converts sound waves in the air into electrical impulses for the brain. Sound enters the external auditory canal and meets the tympanic membrane, which vibrates in response.
Lower pitched sounds (lower frequency) cause a slower vibration rate, and lower volume sounds (lower amplitude) produce less dramatic vibrations. Conversely, higher frequency sounds cause faster vibrations of the tympanic membrane.
The tympanic membrane connects to three auditory ossicles: the malleus, incus, and stapes. These bones pivot together, transmitting the frequency and amplitude information from the tympanic membrane's vibrations to the inner ear. Ligaments hold these ossicles in place, creating a pivotal axis for their movement.
The vibrations from the tympanic membrane are transferred through the ossicles to the footplate of the stapes. The stapes then moves in a piston-like action, sending vibrations into the bony labyrinth, which is filled with perilymph. The flexibility of the round window allows the perilymph to be displaced, enabling vibrations to enter the labyrinth.
The spiral portion of the bony labyrinth is called the cochlea. Vibrations ascend to the apex via the scala vestibuli and descend via the scala tympani. Between these two fluid-filled passages is the cochlear duct, filled with endolymph, separated by Reissner's membrane and the basilar membrane.
The flexible membranes (Reissner's and basilar) move in response to the vibrations. The organ of Corti, located on the basilar membrane, is stimulated by these vibrations. Specialized 'hair cells' within the organ of Corti, covered by the tectorial membrane, generate nerve impulses when their tiny hairs bend against the tectorial membrane, sending signals to the brain via the cochlear nerve.
The basilar membrane does not vibrate uniformly. Different areas respond to different frequencies: lower frequencies vibrate closer to the apex of the cochlea, while higher frequencies vibrate closer to the base. This arrangement is known as tonotopic organization, allowing for the perception of various sounds.