ABSTRACT
Hair cells are the sensory receptors in the inner ear. Auditory hair cells in the cochlea detect pressure waves to mediate hearing. Vestibular hair cells in semicircular canals, utricule, and saccule detect head movement and orientation. Mechanical stimuli such as sound pressure, acceleration, or gravity arrive through the extracellular structure at the hair bundle where it is turned into neural spike-train signals. Histological studies have enhanced the knowledge on the hair bundle structure. Among the endings are the various linkages that connect the cilia, and the more prominent of these are tip links. The earliest stiffness measurements of hair bundles were made using the guinea pig cochlea, turtle cochlea, and bullfrog sacculus. A hair cell is most sensitive when the hair bundle defects along the bilateral symmetric line, called the E-I axis. While the single-degree-of-freedom model contributed to the improvement and the understanding of hair cell mechanotransduction, there were approaches more focused on hair bundle mechanics itself.
