How We Hear
The Rehabilitation Services Department
How We Hear
Sound Waves: Sound waves enter and travel down the ear canal, then vibrate against the eardrum, which vibrates like the head of drum. This motion moves three bones - the hammer, anvil and stirrup - further amplifying the sound signals. Next, the stirrup pushes against the opening to the inner ear (or cochlea), creating traveling waves of liquid motion that sensory cells in the cochlea detect. Cells in different places detect distinct sound tones, allowing us to distinguish among them.
Hair Cells: Inner hair cells and outer hair cells, both in the cochlea, play critical roles in hearing. Surrounded by fluid, they sense movements caused by the stirrup.
Outer Hair Cells: They greatly increase our sensitivity to sound. When the fluid rocks the tuft of hair-like structures at their tip, the outer hair cells start moving, disturbing the fluid even more.
Inner Hair Cells: They sense sounds when their own hair-like bundles are stimulated by movements in the fluid. This movement excites the cells, causing them to send messages to the brain.
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