Endolymph

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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]

Contents 1 Composition 2 Pathology 3 See also 4 Additional images 5 References 6 External links

[edit] 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.

[edit] Pathology

Disruption of the endolymph due to jerky movements (like spinning around or driving over bumps while riding in a car) can cause motion sickness.^[2] A condition where the volume of the endolymph is greatly enlarged is called endolymphatic hydrops and has been linked to Ménière's disease^[3].

[edit] See also

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

[edit] Additional images

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

[edit] References

1. ^ synd/2926 at Who Named It
2. ^ What makes people dizzy when they spin?
3. ^ Meniere's Disease Information Center - Cause of Meniere's Disease

[edit] External links

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

v • d • e Sensory system: Auditory and Vestibular systems Outer ear Pinna (Helix, Antihelix, Tragus, Antitragus, Earlobe) • Ear canal Middle ear Eardrum (Umbo) • Ossicles (Malleus, Incus & Stapes) • muscles (Stapedius, Tensor tympani) • Eustachian tube (Torus tubarius) Inner ear/Labyrinth Bony labyrinth (Vestibule) • Membranous labyrinth Oval window → Scala vestibuli / Reissner's/vestibular membrane, Helicotrema and Scala tympani / Basilar membrane (Perilymph) → Round window Cochlea: Modiolus • Cochlear duct / scala media (Endolymph, Stria vascularis, Spiral ligament, Organ of Corti), Olivocochlear system Organ of Corti: Stereocilia • Sulcus spiralis (externus, internus) • Limbus spiralis to brain (auditory) Tectorial membrane → Hair cells → Spiral ganglion → Cochlear nerve VIII → Cochlear nuclei → Trapezoid body → Superior olivary nuclei → Lateral lemniscus → Inferior colliculi → Medial geniculate nuclei → Auditory radiations → Primary auditory cortex Vestibular system Static/translations: Utricle (Macula) – Saccule (Macula, Endolymphatic sac, Endolymphatic duct) – Kinocilium – Otolith Kinetic/rotations: Semicircular canals (Superior, Posterior, Horizontal) • Cupula • Ampullae (Crista ampullaris) to brain (vestibular) Vestibular nerve VIII → Vestibular nuclei, Flocculonodular lobe Vestibular nuclei → Vestibulospinal tract, Ventral posterolateral nucleus → Vestibular cortex