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

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

Answer: (B)

The auditory system uses a place-based map of frequency along the cochlea. The basilar membrane is stiffer and narrower at the base, so high-frequency vibrations peak there; it becomes wider and more flexible toward the apex, where low-frequency vibrations peak. Hair cells transduce the local motion of the basilar membrane into neural signals, so the hair cells at a given location respond best to the frequency that produces maximal deflection at that spot. Consequently, hair cells at the apex are most strongly activated by low-frequency sounds and respond less to high frequencies. This is why the apex is associated with low-frequency encoding, while high frequencies are encoded near the base.