Episode #10 of the course “How the human body works”
Hearing is our brain’s interpretation of sound waves in the world. The process that allows us to hear happens in a series of specified structures in the head. The ears on either side of the head and the parietal lobes of the brain, which are above and behind the ears, are the only parts used to hear. The inner ear is responsible for helping maintain balance, and it also plays a role in dizziness and vertigo sensations.
The ear is made of three parts: the inner ear, middle ear, and outer ear. Most of it is located inside the head, so only the outer ear is visible. The floppy cartilage attached to the sides of the head—what we commonly call the ears—is the pinna (singular) or pinnae (plural). The pinnae simply funnel sound waves down the ear canal to the eardrum—a thin membrane that vibrates in response to the sound waves that contact it.
On the other side of the eardrum, in the middle ear, are the body’s three smallest bones: the hammer, anvil, and stirrup. They move when the eardrum vibrates, transferring sound waves to the inner ear. The stirrup strikes the cochlea, the inner ear’s spiral-shaped liquid-filled chamber. The liquid moves, bending tiny hairs along the cochlea’s inner walls. These hairs are attached to neurons, and the direction the hair moves because of the liquid informs the neuron what signal about the sound wave to send to the brain. The brain reads this signal and translates it into something you heard.
This process is fast, taking only fractions of a millisecond. However, it is slower than vision; you will always have a microsecond time delay between your brain interpreting something it sees and interpreting something it hears. However, your brain simply erases the gap, so you think you saw and heard it at the same time.
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