Explain frequency place coding (tonotopy) in the cochlea and how pitch is determined.

Explain frequency place coding (tonotopy) in the cochlea and how pitch is determined.

• A. The basilar membrane is uniformly stiff; frequency is coded by firing rate only.
• B. The apex is best for high frequencies; the base for low frequencies.
• C. The base is stiff, responding to high frequencies; the apex is flexible, responding to low frequencies.
• D. Frequency is coded by the cochlear nerve only, independent of place.

Answer: (C)

Frequency place coding, or tonotopy, relies on how the basilar membrane changes along its length. The base is narrow and stiff, while the apex is wide and flexible. When a sound enters the cochlea, a traveling wave forms and peaks at a location determined by frequency: high-frequency sounds drive the base where the membrane is stiffest, and low-frequency sounds drive the apex where it is most flexible. Hair cells at the peak of this motion bend their stereocilia, triggering neurotransmitter release and activating the corresponding auditory nerve fibers. Because the neural signals from that region maintain the same spatial arrangement as in the cochlea, the brain interprets pitch by the place of maximal activity along the membrane.

Frequency place coding, or tonotopy, relies on how the basilar membrane changes along its length. The base is narrow and stiff, while the apex is wide and flexible. When a sound enters the cochlea, a traveling wave forms and peaks at a location determined by frequency: high-frequency sounds drive the base where the membrane is stiffest, and low-frequency sounds drive the apex where it is most flexible. Hair cells at the peak of this motion bend their stereocilia, triggering neurotransmitter release and activating the corresponding auditory nerve fibers. Because the neural signals from that region maintain the same spatial arrangement as in the cochlea, the brain interprets pitch by the place of maximal activity along the membrane.