Hair cells

Hair cells are the sensory receptors in the inner ear that detect sound and head motion to begin the processes of hearing and balance control. The defining feature of hair cells is the hair bundle, the transduction organelle protruding from their apical surface composed of ordered arrays of stereocilia. Mechanical deflection of the hair bundle, normally induced by physiological stimuli, increases the open probability of mechanically gated cation channels located at the tip of stereocilia. The resulting depolarizing inward current generates a receptor potential. The information encoded in this electrical response is transmitted to the auditory or vestibular afferent nerve fibres via the Ca2+-induced release of neurotransmitter from the hair cell’s basal pole. In this way sensory information is relayed to the brain enabling us to perceive sound and maintain balance. In mammals, hair cell loss causes irreversible balance and hearing impairment because these sensory cells show very little or no regenerative ability.