Question

What is cochlear microphonics?

Answer 1

Cochlear Microphonics is a receptor potential generated by outer hair cells. Its detection in surface recordings is considered a prominent sign of outer hair cell integrity in patients with auditory neuropathy.

Complete answer:
In 1983, Dallos explained cochlear microphonics. Cochlear microphonics (CM) is a response from cochlea that mimics the input stimulus and is a response primarily from the outer hair cells. It is an alternating current in response to an acoustic stimulation.

There is a shearing action which occurs when the tectorial membrane and the basilar membrane move and hair cells begin to move/shear. This creates the chance to generate an electric impulse in the cochlea. When the hair cells move to and fro, it creates alternating current and the cochlear microphonics is created. The cochlea is controlled by two “bio” batteries. The first battery is the hair cells and the second is the stria vascularis.

Additional information:
In ear, the cochlear canal consists of two types of fluid- perilymph and endolymph. The endolymph and the perilymph fluids of the cochlea have different consistencies. This difference in their consistencies creates different electrical potentials which may be either positive or negative. In 1960, Davis defined the positive and negative electrical potentials. He placed the cochlear electrical potentials into four classes- Direct current (DC), Cochlear microphonics (CM), Summating current (SC) and Action potential (AP).

Note: The presence of cochlear microphonics along with the absence of auditory brainstem response (ABR) is used in the diagnosis of Auditory neuropathy spectrum disorder (ANSD). Determination of the presence or absence of CM is an important part of the ANSD battery.