What role does the basilar membrane play in hearing?

What role does the basilar membrane play in hearing?

• A. Conducts auditory nerve impulses
• B. Filters sound exclusively in low frequencies
• C. Acts as a frequency-selective ribbon (tonotopic map)
• D. Pumps endolymph

Answer: (C)

The basilar membrane acts as a mechanical frequency analyzer that creates a place code for sound. Its stiffness changes along its length—from base to apex—the base being narrow and stiff and the apex being wide and floppy. When a particular sound frequency arrives, the membrane vibrates most strongly at a specific location where the local mechanical properties best match that frequency. High frequencies peak near the base, while low frequencies peak toward the apex. This spatial pattern means different groups of hair cells along the organ of Corti are activated depending on the frequency, producing a tonotopic (frequency-ordered) representation of sound. Those hair cells convert the mechanical motion into neural signals: their stereocilia deflect, opening mechanotransduction channels, causing receptor potentials and neurotransmitter release onto auditory nerve fibers that carry the frequency-specific information to the brain. So the basilar membrane’s role is to provide the frequency-selective mechanical input that underlies how we perceive pitch. It does not conduct nerve impulses itself, nor does it pump endolymph, and it does not filter only low frequencies—it provides a gradient of sensitivity along its length.

The basilar membrane acts as a mechanical frequency analyzer that creates a place code for sound. Its stiffness changes along its length—from base to apex—the base being narrow and stiff and the apex being wide and floppy. When a particular sound frequency arrives, the membrane vibrates most strongly at a specific location where the local mechanical properties best match that frequency. High frequencies peak near the base, while low frequencies peak toward the apex. This spatial pattern means different groups of hair cells along the organ of Corti are activated depending on the frequency, producing a tonotopic (frequency-ordered) representation of sound.

Those hair cells convert the mechanical motion into neural signals: their stereocilia deflect, opening mechanotransduction channels, causing receptor potentials and neurotransmitter release onto auditory nerve fibers that carry the frequency-specific information to the brain. So the basilar membrane’s role is to provide the frequency-selective mechanical input that underlies how we perceive pitch. It does not conduct nerve impulses itself, nor does it pump endolymph, and it does not filter only low frequencies—it provides a gradient of sensitivity along its length.