The spiral ligament and stria vascularis of the cochlea are responsible for maintaining the high potassium (K+) concentration of endolymph. The stria vascularis generates the endocochlear potential of approximately +80 mV. Damage to the stria vascularis (as in Meniere disease or aminoglycoside ototoxicity) affects hearing by:

• A Reducing the endocochlear potential, decreasing the driving force for K+ entry into hair cells and thus mechanotransduction ✓
• B Increasing K+ outflow from hair cells, causing depolarisation block
• C Destroying the tectorial membrane, preventing stereocilia deflection
• D Disrupting the helicotrema, preventing pressure equalisation between scala vestibuli and tympani

Explanation

The endocochlear potential (+80 mV) maintained by the stria vascularis in endolymph (high K+, +80 mV) creates a large electrochemical driving force for K+ to enter mechanosensory hair cells through mechanically gated ion channels (tip links) when stereocilia deflect. This K+ influx depolarises the hair cell and triggers neurotransmitter release. Damage to the stria vascularis reduces the endocochlear potential, drastically reducing the driving force for K+ mechanotransduction, and thus hearing sensitivity falls even if the hair cells and tectorial membrane are intact. This mechanism explains why aminoglycoside-induced strial damage causes sensorineural hearing loss.

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

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Written and medically reviewed by the StethoPrep medical team.