The apical turn of the cochlea encodes which sound frequency, and what is the physiological basis for this tonotopic organization?

• A High frequencies (8 kHz) — the apical basilar membrane is narrow and stiff, resonating at high frequencies
• B Mid frequencies (1–2 kHz) — intermediate membrane stiffness at the apex
• C Low frequencies (200–500 Hz) — the apical basilar membrane is wide and flexible (compliant), tuned to low frequencies ✓
• D All frequencies equally — tonotopy is not determined by membrane properties but by neural coding

Explanation

The cochlea is organized tonotopically: the base encodes high frequencies (10–20 kHz) because the basilar membrane is narrow, thin, and stiff; the apex encodes low frequencies (200–500 Hz) because it is wide, thick, and compliant (flexible). This is the basis of the 'traveling wave' theory proposed by Von Bekesy (Nobel Prize 1961). The stiffness gradient along the basilar membrane determines the frequency-place map, not simply neural coding alone.

Reference: Dhingra Diseases of Ear, Nose and Throat, 7th ed.

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Written and medically reviewed by the StethoPrep medical team.