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What role do hair cells play in 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.

Hair cells are the essential sensory receptors within the organ of Corti that transduce mechanical sound vibrations into electrical nerve impulses.12

Mechanism of Transduction

When sound waves cause the basilar membrane to vibrate, shearing forces are created between the reticular lamina and the tectorial membrane. This movement displaces the stereocilia—stiff, hairlike projections on top of the hair cells.12

Depolarization: When stereocilia bend toward their longest length, ion channels open, allowing potassium ions to flow into the cell. This depolarizes the hair cell and triggers the release of neurotransmitters at the cell's base.1
Transmission: These neurotransmitters stimulate the nerve fibres of the cochlear nerve, which then carry the signal to the brain.12

Functional Roles

Inner Hair Cells: These are the primary sensory receptors that transmit the majority of auditory information to the brain.12
Outer Hair Cells: These cells act as mechanical-electrical stimulators and feedback elements. They can contract rhythmically to modify and enhance the sensitivity and frequency discrimination of the inner hair cells.1