The human ear consists of several parts, the ear canal, the middle ear, and the inner ear. Sound waves travel down the ear canal in the form of compression pressure waves. These pressure waves induce deflection of the eardrum, and the various structures attached to it. Part of this structure is coupled to the inner ear in a way which seems to produce an outward deflection in reaction to an inward pressure force. The inner ear is configured as a spiral with two chambers. One of the chambers is connected to the eardrum through the mechanism described above, while the other is in acoustic contact with the eardrum. The apparent result of all of this complexity is the development of an oscillating force between the chambers of the inner ear.
The inner ear is a seashell-like spiral structure, in which the two chambers are separated by a thin diaphragm impregnated with rapid adapting mechanoreceptors. Acoustic signals produce oscillations in this diaphragm. One effect of the shape of the spiral diaphragm is that the resonant frequency is a function of position along the spiral. As a result, any particular acoustic signal frequency will produce a mechanical oscillation in the inner ear at a particular physical location. In this way, the inner ear acts as an acoustic spectrum analyzer, with individual mechanoreceptors configured for detection of particular audio frequencies. The central nervous system receives all of these signals and processes them into recognizable patterns os sound, including human speech.
