How does the basilar membrane contribute to sound discrimination?

How does the basilar membrane contribute to sound discrimination?

• A. It secretes endolymph in response to sound.
• B. It amplifies sound via motor proteins.
• C. It varies in width and stiffness, allowing for frequency discrimination.
• D. It filters out low frequencies by dampening.

Answer: (C)

The basilar membrane has a gradient in width and stiffness along the length of the cochlea, which is what enables frequency discrimination. The base is narrow and stiff, so it resonates best to high-frequency sounds, while the apex is wide and flexible, resonating best to low-frequency sounds. When sound enters the cochlea, a traveling wave forms on the basilar membrane and reaches a peak location that depends on the frequency. This localized displacement bends the hair cell stereocilia at that spot, initiating receptor potentials and sending frequency-specific signals to the brain. This spatial mapping of frequency along the membrane is the core way it contributes to distinguishing different pitches. Endolymph secretion, motor-protein–driven amplification by outer hair cells, and simple dampening of low frequencies do not describe this property of the basilar membrane.

The basilar membrane has a gradient in width and stiffness along the length of the cochlea, which is what enables frequency discrimination. The base is narrow and stiff, so it resonates best to high-frequency sounds, while the apex is wide and flexible, resonating best to low-frequency sounds. When sound enters the cochlea, a traveling wave forms on the basilar membrane and reaches a peak location that depends on the frequency. This localized displacement bends the hair cell stereocilia at that spot, initiating receptor potentials and sending frequency-specific signals to the brain. This spatial mapping of frequency along the membrane is the core way it contributes to distinguishing different pitches. Endolymph secretion, motor-protein–driven amplification by outer hair cells, and simple dampening of low frequencies do not describe this property of the basilar membrane.