The endocochlear potential (EP; also called endolymphatic potential) is the positive voltage of 80-100mV seen in the cochlear endolymphatic spaces. Within the cochlea the EP varies in the magnitude all along its length. When a sound is presented, the endocochlear potential changes either positive or negative in the
endolymph
Endolymph is the fluid contained in the membranous labyrinth of the inner ear. The major cation in endolymph is potassium, with the values of sodium and potassium concentration in the endolymph being 0.91 mM and 154 mM, respectively. I ...
, depending on the stimulus. The change in the potential is called the
summating potential.
With the movement of the
basilar membrane
The basilar membrane is a stiff structural element within the cochlea of the inner ear which separates two liquid-filled tubes that run along the coil of the cochlea, the scala media and the scala tympani. The basilar membrane moves up and down ...
, a shear force is created and a small potential is generated due to a difference in potential between the endolymph (
scala media
Scala or SCALA may refer to:
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Music
* Scala (band), an English electronic music group
* Escala (group), an electronic string quartet formerly known ...
, +80 mV) and the perilymph (vestibular and tympanic ducts, 0 mV). EP is highest in the basal turn of the cochlea (95 mV in mice) and decreases in the magnitude towards the apex (87 mV). In saccule and utricle, endolymphatic potential is about +9 mV and +3mV in the semicircular canal. EP is highly dependent on the metabolism and ionic transport.
An acoustic stimulus produces a simultaneous change in conductance at the membrane of the receptor cell. Because there is a steep gradient (150 mV), changes in membrane conductance are accompanied by rapid influx and efflux of ions which in turn produce the receptor potential. This is known as the Battery Hypothesis. The receptor potential for each hair cell causes a release of neurotransmitter at its basal pole, which elicits excitation of the afferent nerve fibres.
Anatomy