What is the endocochlear potential, and why is it important for hearing?

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Diagram showing auditory mechanisms in insects, including labeled illustrations of a scolophore organ, the mosquito ear with antenna shaft and scolophores, the cicada ear with auditory capsule and tympanic membrane, and the grasshopper ear with sensory body and tympanic membrane. — sound reception Auditory mechanisms in insects. (Left) A scolophore organ. (Top right) The mosquito ear. (Centre right) The ear of the cicada *Magicicada septendecim*. (Bottom right) The ear of the grasshopper.

The endocochlear potential is a direct current potential difference of approximately +80 millivolts that exists between the endolymph and the perilymph within the cochlea. This potential is maintained by the stria vascularis, which continually transports potassium ions from the perilymph into the cochlear duct.1

This potential is essential for hearing because it creates a steep electrical gradient between the endolymph and the interior of the hair cells, which have a negative intracellular potential. This gradient, particularly at the tips of the hair cells, is believed to sensitize the cells, allowing them to detect even the slightest sound vibrations. When sound causes the stereocilia to bend, this electrical environment facilitates the flow of ions that depolarizes the hair cell, triggering the release of neurotransmitters and the subsequent transmission of nerve impulses to the brain.1