Sound Waves to Brain Waves — Sound’s Journey from the Ear to the Brain

By Andrea Subitoni Antonio

What, exactly, is sound? And how does it get to your brain? And even then — how does your brain understand it? Dr. Ligia Subitoni Antonio of the University of Nevada, Reno Department of Physiology and Cell Biology has the answers.

“Sound waves are mechanical waves,” says Dr. Antonio, “And they spread, horizontally, from [their] source.” One might imagine dropping an object inside a glass of water and watching ripples form on the surface and then move outward. “The vibrations create a frequency of ‘regions.’ These regions are where the air is either less dense or more compressed. The sound then travels through the ear, where it vibrates the tympanic membrane.”

The tympanic membrane — colloquially known as the eardrum — is a thin, cone-shaped membrane that separates the external ear (or, ear canal) from the middle ear.

“The sound continues to the ossicles of the middle ear,” says Dr. Antonio, “And then it reaches the auditory portions of the inner ear — that’s the cochlea,” she says, demonstrating towards a horn-shaped structure with two chambers separated by another membrane.

The liquid inside the two chambers of the cochlea moves in accordance with the sound waves, and the wall that separates them — the basilar membrane — takes the shape of the sound frequency differentiation that occurs. This information is taken in by tiny cellular cilia (hairlike cells), which bend with these ripples, and is converted from its mechanical state (sound waves) to an electrical one (brain waves).

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