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SEPARATION OF FLUIDS The basilar membrane within the Cochlea of the inner ear separates two liquid filled tubes that run along the coil of the cochlea, the Scala Media and the Scala Tympani (see figure). The fluids in these two tubes, the Endolymph and the Perilymph are very different chemically, biochemically, and electrically. Therefore they have to be kept strictly separated. This separation is the main function of the basilar membrane in the hearing organ of all land Vertebrates . A leakage between the two tubes, due to an injury, causes a disruption or even a total breakdown of hearing in that ear. A ''BASE'' FOR THE SENSORY CELLS Closely associated with the function of separating the two fluids is the function of providing a ''base'' for the sensory cells of hearing, the Hair Cells (see figure). This function gave the ''basilar'' membrane its name, and it is again present in all land vertebrates. Due to its location, the basilar membrane places the hair cells in a position where they are adjacent to both the endolymph and the perilymph, which is a precondition of hair cell function. FREQUENCY DISPERSION A third, evolutionarily younger, function of the basilar membrane is strongly developed in the cochlea of most mammalian species and weakly developed in some bird species. It is the function of frequency Dispersion of incoming sound waves. In brief, the membrane is tapered and it is stiffer at one end than at the other. This causes sound input of a certain frequency to vibrate a particular location of the membrane more than other locations due to the physical property of Resonance . As shown in experiments by Nobel Prize laureate Georg Von Békésy , high frequencies lead to maximum vibrations at the basal end of the cochlear coil (narrow membrane), and low frequencies lead to maximum vibrations at the apical end of the cochlear coil (wide membrane). REFERENCES
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