What is the role of hair cells at the base of the cochlea?

• A. Activated by all frequencies
• B. Activated only by low frequencies
• C. Activated only by high frequencies
• D. Not involved in hearing

Answer: (C)

The place in the cochlea where hair cells sit determines which frequencies they respond to. The base is stiff and narrow, so it vibrates best to high-frequency sounds. When a high-frequency component enters the cochlea, the basilar membrane at the base deflects most there, bending the hair cells and triggering neural signals to the auditory nerve. So these hair cells are primarily activated by high frequencies. (Lower frequencies peak toward the apex, and the base is not driven by all frequencies.) This organization underlies how we perceive different pitches through a mechanism called tonotopy.