The spiral organ of Corti, the receptor organ for hearing, sits on the basilar membrane within the scala media. The endolymph that bathes its stereocilia has a unique ionic composition. Which ion is present at an unusually HIGH concentration in endolymph (compared to most extracellular fluids) and is essential for the mechanoelectrical transduction current?
- A Potassium (K+) ✓
- B Sodium (Na+)
- C Calcium (Ca2+)
- D Chloride (Cl-)
Explanation
Endolymph (filling scala media/cochlear duct) has a unique composition resembling intracellular fluid: very high potassium (~150 mEq/L) and very low sodium (~1 mEq/L). This is in contrast to perilymph (filling scala vestibuli and tympani), which resembles extracellular fluid (high Na+, low K+). The high K+ endolymph maintains the endocochlear potential (+80 mV) generated by the stria vascularis. When sound deflects stereocilia, mechanically gated K+ channels (MET channels, containing TMIE/TMC1) open and K+ flows into the hair cell down its electrochemical gradient, depolarizing it. K+ recycling via gap junctions back to the stria vascularis is essential.
Reference: BD Chaurasia's Human Anatomy, 8th ed.
High-yield for: NEET PGINI-CETNExTFMGEUSMLEPLABMRCP
Written and medically reviewed by the StethoPrep medical team.