Perilymph

Perilymph
Cross-section of cochlea. Perilymph is located in the scala vestibuli and scala tympani - the aqua regions at the top and bottom of the diagram.
Cross-section of semi-circular canal and duct showing perilymphatic space
Details
Identifiers
Latin	perilympha
TA	A15.3.03.056
FMA	60908
Anatomical terminology []

Perilymph (also known as Cotunnius' liquid, and liquor cotunnii) is an extracellular fluid located within the cochlea (part of the inner ear) in two of its three compartments: the scala tympani and scala vestibuli. The ionic composition of perilymph is comparable to that of plasma and cerebrospinal fluid. The major cation (positively charged ion) in perilymph is sodium: The values of sodium and potassium concentration in the perilymph are 138 mM and 6.9 mM, respectively.

The inner ear has two parts: the bony labyrinth and the membranous labyrinth. The membranous labyrinth is contained within the bony labyrinth, and contains a fluid called endolymph. Between the outer wall of the membranous labyrinth and the wall of the bony labyrinth is the perilymphatic space which contains the perilymph. The membranous labyrinth is suspended in the perilymph. The perilymph in the bony labyrinth is continuous with the cerebrospinal fluid of the subarachnoid space via the perilymphatic duct.

Perilymph and endolymph have unique ionic compositions suited to their functions in regulating electrochemical impulses of hair cells. The electric potential of endolymph is ~80-90 mV more positive than perilymph due to a higher concentration of potassium cations (K⁺) than sodium (Na⁺).