The cochlea performs frequency analysis and amplification of sounds. was reversed

The cochlea performs frequency analysis and amplification of sounds. was reversed at the apical (low frequency) location. Unlike the basilar membrane stiffness varying by a factor of 1700 along the cochlear length, Ponatinib the stiffness FOXO3 of the organ of Corti complex felt by the outer hair cell remained between 1.5 and 0.4 times the outer hair cell stiffness. The Y-shaped structure in the organ of Corti created by outer hair cell, Deiters cell and its phalange was the main Ponatinib determinant of the elastic reactance imposed on the outer hair cells. The stiffness and geometry of the Deiters cell and its phalange affected cochlear amplification differently depending on the location. Introduction The organ of Corti of the mammalian cochlea is usually uniquely organized with structurally significant sensory receptor cells and their supporting cells that Ponatinib suggest their mechanical role [1,2]. The inner and outer pillar cells form a triangular tunnel throughout the cochlear length. The Deiters cells, their phalangeal processes and the outer hair cells form a repeating structural pattern resembling the truss structure of a bridge. The organ of Corti is usually sandwiched between two matrices reinforced with collagen fibers, the tectorial membrane (TM) and the basilar membrane (BM). The longitudinally graded stiffness of the BM forms the physical basis for the characteristic cochlear touring dunes [3], and the tonotopy of the mammalian cochlea [4,5]. The organ of Corti complex (OCC: the organ of Corti, the TM and the BM) vibrates due to hydrodynamic pressure. The comparative vibrations between OCC structures deflect the stereocilia package of the hair cells (hair package) to activate the mechano-transduction channels at the suggestions of the hair package [6]. The mechano-transduction current modulates the cells membrane potential. While inner hair cells mechano-transduction results in the activation of afferent nerve fibers attached to the cell, the mechano-transduction of the outer hair cell has a different roleto provide mechanical opinions to the OCC [7]. At least two force-generating mechanisms have been recognized in the outer hair cells. The action of mechano-transduction channels can produce a shear pressure between the TM and the top surface of the organ of Corti through the hair package [8,9]. Upon electrical potential switch across the cells lateral membrane, the outer hair cell generates pressure along the axis of the cell length called the somatic motility [10,11]. Experimental evidence supports that the somatic motility plays a crucial role in cochlear amplification [12,13]. Some theoretical studies suggest that the somatic motility is usually sufficient to amplify the cochlear vibrations [14C16], while others support that both active mechanisms operate together for amplification and tuning of the cochlea [17]. For the active pressure of the outer Ponatinib hair cell to amplify the vibrations of the OCC, two basic conditions must be satisfied: the pressure magnitude must be large enough to overcome the impedance imposed on the actuators (outer hair cells), and be fast enough to operate at high frequencies > 50 kHz in some species. Regarding the velocity of pressure generation, the velocity of hair package motility, limited by the adaptation velocity of transduction channels, was assessed up to a few kHz [18]. The cutoff frequency due to the membranes RC time constant was also assessed up to a few kHz [19], and that assessed RC time constant was shown to be small enough to amplify OCC vibrations at high Ponatinib frequencies above 40 kHz.