| Endolymph | |
|---|---|
 Cross-section ofcochlea. (Endolymph is located in thecochlear duct - the light green region at the middle of the diagram.) | |
 illustration of otolith organs showing detail ofutricle,ococonia, endolymph, cupula,macula,hair cell filaments, andsaccular nerve | |
| Details | |
| Identifiers | |
| Latin | endolympha |
| MeSH | D004710 |
| TA98 | A15.3.03.061 |
| TA2 | 6997 |
| FMA | 61112 |
| Anatomical terminology | |
Endolymph is the fluid contained in themembranous labyrinth of theinner ear. The majorcation in endolymph ispotassium, with the values ofsodium andpotassium concentration in the endolymph being 0.91 mM and 154 mM, respectively.[1] It is also calledScarpa's fluid, afterAntonio Scarpa.[2]
Theinner ear has two parts: thebony labyrinth and themembranous labyrinth. The membranous labyrinth is contained within the bony labyrinth, and within the membranous labyrinth is a fluid called endolymph. Between the outer wall of the membranous labyrinth and the wall of the bony labyrinth is the location of perilymph.
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 K compared to Na.[3]
The main component of this unique extracellular fluid ispotassium, which is secreted from thestria vascularis. The high potassium content of the endolymph means that potassium, not sodium, is carried as the de-polarizing electric current in the hair cells. This is known as themechano-electric transduction (MET) current.
Endolymph has a high positive potential (80–120 mV in the cochlea), relative to other nearby fluids such as perilymph, due to its high concentration of positively charged ions. It is mainly this electrical potential difference that allows potassium ions to flow into the hair cells during mechanical stimulation of the hair bundle. Because the hair cells are at a negative potential of about −50 mV, the potential difference from endolymph to hair cell is on the order of 150 mV, which is the largest electrical potential difference found in the body.[citation needed]
Disruption of the endolymph due to jerky movements (like spinning around or driving over bumps while riding in a car) can causemotion sickness.[4] A condition where the volume of the endolymph is greatly enlarged is called endolymphatic hydrops and has been linked toMénière's disease.[5]
