What is the name of the fluid in the inner ear responsible for balance? The fluid is called endolymph.
Endolymph fills the membranous labyrinth, a system of chambers and tubes inside the inner ear. In the semicircular canals, head rotation makes the endolymph move relative to sensory structures, bending hair cells and signaling angular acceleration to the brain. The utricle and saccule also use endolymph and sensory organs to help detect linear acceleration and head position.
Endolymph is unusual because it is rich in potassium and relatively low in sodium. This composition creates the electrical conditions that allow inner-ear hair cells to convert mechanical movement into nerve signals. Endolymph therefore contributes to both balance and hearing: it also moves within the cochlear duct when sound vibrations enter the inner ear.
A common mix-up is perilymph, the fluid surrounding the membranous labyrinth inside the bony labyrinth. Perilymph and endolymph occupy different compartments and have different chemistry, although both support inner-ear function. Excessive endolymph volume is called endolymphatic hydrops and has been associated with Ménière's disease.