The basilar membrane's frequency-selectivity arises from which characteristic?

The basilar membrane's frequency-selectivity arises from which characteristic?

• A. Uniform stiffness along its length.
• B. A constant width along its length.
• C. Variation in width and stiffness along its length.
• D. Active amplification by outer hair cells.

Answer: (C)

Frequency selectivity on the basilar membrane arises from graded mechanical properties along its length. The base is narrow and stiff, while the apex is wider and more compliant. This gradient sets a different local resonant frequency at each point: high frequencies preferentially drive the stiff, narrow base, whereas low frequencies drive the flexible, broad apex. As a sound travels as a traveling wave along the membrane, energy concentrates where the local impedance matches the stimulus frequency, producing a peak vibration at that location. Outer hair cell amplification can sharpen and enhance this tuning, but the fundamental frequency-to-place mapping comes from the variation in width and stiffness along the membrane. Uniform stiffness or constant width would not produce this organized frequency-specific activation.

Frequency selectivity on the basilar membrane arises from graded mechanical properties along its length. The base is narrow and stiff, while the apex is wider and more compliant. This gradient sets a different local resonant frequency at each point: high frequencies preferentially drive the stiff, narrow base, whereas low frequencies drive the flexible, broad apex. As a sound travels as a traveling wave along the membrane, energy concentrates where the local impedance matches the stimulus frequency, producing a peak vibration at that location. Outer hair cell amplification can sharpen and enhance this tuning, but the fundamental frequency-to-place mapping comes from the variation in width and stiffness along the membrane. Uniform stiffness or constant width would not produce this organized frequency-specific activation.