The organ of Corti is the peripheral receptor for hearing. Which specific cell type synapses with the auditory nerve (spiral ganglion neurons) and what is the approximate ratio of inner to outer hair cells in the cochlea?

• A Outer hair cells are the primary afferent sensory cells; inner hair cells are primarily efferent
• B Inner hair cells are the primary afferent sensory cells; ~3,500 inner hair cells receive ~95% of afferent innervation; ~12,000 outer hair cells amplify basilar membrane motion via electromotility ✓
• C Both inner and outer hair cells equally share afferent innervation; inner/outer ratio is 1:1
• D Pillar cells (rods of Corti) are the primary transducers and synapse with the cochlear nerve

Explanation

Inner hair cells (IHCs, approximately 3,500) are the primary sensory cells: they receive ~90–95% of afferent fibres from the spiral ganglion neurons (type I neurons, myelinated). Outer hair cells (OHCs, approximately 12,000, arranged in 3 rows) receive predominantly efferent olivocochlear fibres and are responsible for active amplification of basilar membrane vibration (cochlear amplifier) via electromotility — length changes driven by prestin, a membrane motor protein. Destruction of OHCs (e.g., by aminoglycosides, noise trauma) reduces sensitivity by ~40–60 dB. Pillar cells and Deiters' cells provide structural support; they do not transduce sound.

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

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