endolymph

Endolymph
Cross-section of cochlea. (Endolymph is located in the scala media - the light green region at the middle of the diagram.)
illustration of otolith organs showing detail of utricle, ococonia, endolymph, cupula, macula, hair cell filaments, and saccular nerve
Latin	endolympha
Gray's	subject #232 1051
MeSH	Endolymph
Dorlands/Elsevier	e_08/12332247

Endolymph is the fluid contained in the membranous labyrinth of the inner ear.

It is also called Scarpa's fluid, after Antonio Scarpa.^[1]

Composition

The main cation 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 depolarizing electrical current in the hair cells. This is known as the mechano-electric transduction (MET) current.

Endolymph has a high positive charge (from 80-120 mV in the cochlea), mainly due to the presence of positively-charged amino acids. It is mainly this electrical gradient that allows potassium ions to flow into the negatively-charged hair cells during mechanical stimulation of the hair bundle. Because the hair cells are at a negative potential of about -50 mV, the electrical gradient from endolymph to hair cell is on the order of 150 mV, which is the largest electrical potential found in the body.

Pathology

Disruption of the endolymph due to jerky movements (like driving over bumps while riding in a car) can cause motion sickness^{[citation needed]}. A condition where the volume of the endolymph is greatly enlarged is called endolymphatic hydrops and has been linked to Ménière's disease^[2].

See also

• Perilymph
• Stria vascularis
• Organ of Corti
• Ménière's disease

Additional images

Inner ear illustration showing semicircular canal, hair cells, ampulla, cupula, vestibular nerve, & fluid

References

External links

• Endolymph at eMedicine Dictionary
• Longitudinal Flow of Endolymph at wustl.edu

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