Overview / Physics / Fluids / Stria
Drawings: S. Blatrix

Inner ear fluids

The cochlea contains 3 spiral ducts filled with fluids: perilymph in the tympanic and vestibular ducts, endolymph in the cochlear duct. These fluids are essential to the functioning of the sensory cells of the inner ear. For instance, an abnormal endolymph production causes Menière's disease resulting in both vestibular and cochlear dysfunction.

Perilymph and endolymph

The perilymph (blue) and endolymph (red) differ in their ionic contents.

The endolymph composition, with a high potassium and a low sodium concentration, resembles the cytosol. In contrast, the perilymph composition is closer to the extracellular medium, with a low potassium but a high sodium content. The differing ionic composition results in a roughly 80 mV difference in potential between the endolymph and the perilymph.

Ionic composition (mM)
  Perilymph Endolymph

Endolymphatic potential
The endolymphatic potential (around 80 mV) depends on an active secretion of K+ , which involves fibroblasts, different support cells and the the stria vascularis. The electro-chemical K+ gradient accounts for hair cell depolarisation (excitation). An active K+ recycling mechanism (after this transduction process) involves support cells surrounding the hair cells and thus the high concentration of K+ in the endolymph is maintained.

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