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The cochlea (pl.: cochleae) is a spiraled, hollow, conical chamber of bone, in which waves propagate from the base (near the middle ear and the oval window) to the apex (the top or center of the spiral).
The second mechanism is a non-linear active mechanism, which is primarily dependent on the functioning of the OHCs, and also the general physiological condition of the cochlea itself. The base and apex of the basilar membrane differ in stiffness and width, which cause the basilar membrane to respond to varying frequencies differently along its ...
The basilar membrane is widest (0.42–0.65 mm) and least stiff at the apex of the cochlea, and narrowest (0.08–0.16 mm) and stiffest at the base (near the round and oval windows). [3] High-frequency sounds localize near the base of the cochlea, while low-frequency sounds localize near the apex.
The cochlea has three fluid-filled sections (i.e. the scala media, scala tympani and scala vestibuli), and supports a fluid wave driven by pressure across the basilar membrane separating two of the sections. Strikingly, one section, called the cochlear duct or scala media, contains endolymph. The organ of Corti is located in this duct on the ...
The base of the cochlea, closest to the outer ear, is the most stiff and narrow and is where the high-frequency sounds are transduced. The apex, or top, of the cochlea is wider and much more flexible and loose and functions as the transduction site for low-frequency sounds. [7]
The cochlea is tonotopically mapped in a spiral fashion, with lower frequencies localizing at the apex of the cochlea, and high frequencies at the base of the cochlea, near the oval and round windows. With age, comes a loss in distinction of frequencies, especially higher ones.
The height of hair bundles increases from base to apex and the number of stereocilia decreases (i.e. hair cells located at the base of the cochlea contain more stereo cilia than those located at the apex). [14] Furthermore, in the tip-link complex of cochlear hair cells, tonotopy is associated with gradients of intrinsic mechanical properties. [15]
For example, lower frequencies mostly stimulate the apex, in comparison to higher frequencies, which stimulate the base of the cochlea. This attribute of the physiology of the basilar membrane can be illustrated in the form of a place–frequency map: [12] Simplified schematic of the basilar membrane, showing the change in characteristic ...