In the cochlea, the travelling wave from base to apex reaches its peak displacement at a location that depends on sound frequency. For a high-frequency sound (e.g., 8000 Hz), the peak basilar membrane displacement occurs at the:
- A Apex (helicotrema end) — widest, most compliant portion
- B Middle third of the cochlear duct
- C Base (oval window end) — stiffest, narrowest portion ✓
- D Tectorial membrane rather than the basilar membrane
Explanation
The basilar membrane has a tonotopic organisation: it is narrow and stiff at the base (near the oval window) and wide and compliant at the apex. High-frequency sounds produce maximum displacement at the basal end, while low-frequency sounds displace the membrane maximally at the apical end. This frequency-place coding is the basis of tonotopy. Hair cells at the base respond to high-frequency sounds (5–20 kHz), while apical hair cells respond to low frequencies (20–500 Hz). Hearing loss for high frequencies (presbycusis, noise-induced) characteristically damages basal hair cells first.
Reference: Guyton & Hall, Textbook of Medical Physiology, 14th ed.
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Written and medically reviewed by the StethoPrep medical team.