The organ of Corti sits on the basilar membrane within the scala media (cochlear duct). Hair cells transduce mechanical vibration into electrical signals. The inner hair cells (IHC) versus outer hair cells (OHC) have which different functional roles?

• A OHCs receive most afferent innervation and send sound signals to the auditory cortex; IHCs are purely efferent
• B IHCs detect high frequencies; OHCs detect low frequencies based on position in the organ of Corti
• C Both IHC and OHC have equal afferent and efferent innervation ratios
• D IHCs are the primary afferent receptors (receive most afferent innervation); OHCs are motor amplifiers (electromotility via prestin) that amplify basilar membrane motion ✓

Explanation

There are approximately 3,500 inner hair cells and 12,000 outer hair cells in the cochlea. The inner hair cells receive about 95% of the afferent innervation from Type I spiral ganglion neurons — they are the primary acoustic sensors transmitting information via CN VIII to the auditory brainstem. The outer hair cells are primarily innervated by efferent olivocochlear fibers and function as cochlear amplifiers: their unique motor protein prestin (a voltage-gated motor in the lateral membrane) causes electromotility (length changes up to 10 kHz), amplifying basilar membrane motion by up to 40 dB. Selective OHC loss (aminoglycosides, noise) causes sensorineural hearing loss before IHC loss.

Reference: BD Chaurasia's Human Anatomy, 8th ed.

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