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Cross-section of cochlea. (Endolymph is located in the scala media - the light green region at the middle of the diagram.)
Latin endolympha
Gray's p.1051
MeSH A12.207.270.517.324
TA A15.3.03.061
FMA 61112
Anatomical terminology

Endolymph is the fluid contained in the membranous labyrinth of the inner ear. It is also called Scarpa's fluid, after Antonio Scarpa.[1]


The inner ear has two parts: the bony labyrinth and the membranous 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.



The main component of this unique extracellular fluid is potassium, which is secreted from the stria vascularis. The high potassium content of the endolymph means that potassium, not sodium, is carried as the de-polarizing electrical current in the hair cells. This is known as the mechano-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]


Fluid waves occur in the endolymph in the various parts of the membranous labyrinth in response to fluid waves in the perilymph.

  • Hearing: Cochlear duct: fluid waves in the endolymph of the cochlear duct stimulate the receptor cells, which in turn translate their movement into nerve impulses that the brain perceives as sound.
  • Balance: Semicircular canals: angular acceleration of the endolymph in the semicircular canals stimulate the vestibular receptors of the endolymph. The semicircular canals of both inner ears act in concert to coordinate balance.

Clinical significance[edit]

Disruption of the endolymph due to jerky movements (like spinning around or driving over bumps while riding in a car) can cause motion sickness.[3] A condition where the volume of the endolymph is greatly enlarged is called endolymphatic hydrops and has been linked to Ménière's disease.[4]

Additional images[edit]

See also[edit]


  1. ^ synd/2926 at Who Named It?
  2. ^ Konishi T, Hamrick PE, Walsh PJ (1978). "Ion transport in guinea pig cochlea. I. Potassium and sodium transport". Acta Otolaryngol 86 (1-2): 22–34. doi:10.3109/00016487809124717. PMID 696294. 
  3. ^ What makes people dizzy when they spin?
  4. ^ Ménière's Disease Information Center - Cause of Ménière's Disease

External links[edit]