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Hair cells are the sensory cells of the auditory system that are found within the cochlea's organ of Corti. They derive their name from the tufts of stereocilia which protrude from the apical surface of the cell. Mammalian hair cells come in two functionally distinct types -- the outer and inner hair cells. Modern research has shown that outer hair cells are motile and responsible for stimulus compression and amplification, while the inner hair cells are responsible for transforming the input sound stimulus into a series of action potentials that are relayed via the auditory nerve to the brainstem and auditory cortex.
The deflection of the inner hair cell stereocilia opens mechanically gated ion channels that allows positively charged potassium ions to enter the cell. The influx of positive ions increases the receptor potential of the cell, which in turn, triggers the release of neurotransmitter at the basal end of the cell, via the opening of voltage gated calcium channels. The neurotransmitter diffuses across the synapse and binds to a receptor located on one of numerous auditory nerve fibers that contact each inner hair cell.
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