Endocochlear

Endocochlear refers to the cochlea, the hearing portion of the inner ear, and to the fluid-filled compartments within it. The term is used in anatomy, physiology, and clinical contexts to describe the endolymph-containing spaces and the ionic environments that support auditory transduction. It contrasts with perilymphatic spaces that surround parts of the cochlea.

The cochlea contains three scalae: the scala vestibuli and scala tympani, which hold perilymph, and the scala media (cochlear duct), which contains endolymph. The endolymphatic space is maintained by the stria vascularis, producing endolymph rich in potassium. The organ of Corti rests on the basilar membrane within this endolymphatic compartment, protected by Reissner's membrane.

A key feature of endocochlear physiology is the endocochlear potential, a positive electrical potential (about +80 mV) in the scala media relative to surrounding fluids. This electrochemical gradient enhances the transduction of mechanical vibrations by hair cells, enabling conversion of sound into neural signals.

Clinically, disturbances of the endocochlear system can contribute to sensorineural hearing loss. Endolymphatic hydrops, as seen in Menière's disease, involves excess endolymph within the scala media and related structures. Diagnostic approaches may include audiometry and electrocochleography to assess endocochlear function, while imaging can evaluate the anatomy of the endolymphatic spaces.

Terminology: Endocochlear is used to describe processes and structures inside the cochlea that are bathed in endolymph, in contrast to perilymphatic compartments. It is a foundational concept in inner-ear physiology, audiology, and otology.