As the video shows (above, right), sound vibrations move through the air like waves moving across the water. Hearing begins when the vibrations reach the outer ear (left figure 1), which acts to funnel the vibrations through the ear canal (2) toward the eardrum (3). Sound vibrations then interact with the eardrum, before transferring to a series of three tiny bones in the middle ear (4). These bones further amplify the vibrations of the eardrum, then transfer them to a sensory organ in the inner ear, the cochlea (5). Tiny sensory hair cells lining the cochlea (6) are responsible for transforming the sound waves into electrical signals that are interpreted in the cerebral cortex of the brain (watch the video above, right).
Importance Of The Cochlea
The cochlea changes sound waves into nerve impulses, which are then transferred to the auditory cortex (part of the temporal lobe) of the brain via the auditory nerve, for processing. Processing includes decoding the frequency distribution of the information contained in the neural impulses for meaning and spatial recognition (where is the sound located, and what does it mean).
In the figure below, the cochlea (A & B) is filled with fluid, and lined with tens of thousands of tiny hair cells (C & D). The figures (A-E) show increasingly enlarged electron microscope images of the cochlea and hair cells. Figure A shows a sound wave’s journey to the cochlea.
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