Scientists from Case Western Reserve University School of Medicine have reiterated that people hear sounds when hair bundles located atop hair cells within the inner ear capture energy of sound waves, and convert them into electrical signals that stimulate auditory nerves to the brain.
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The scientists reveal that stereocilia or hair-like projections are what constitutes hair bundles, and these move together with other stereocilia. Where the stereocilia moves in a whipsaw motion in response to loud noises, it could result in permanent hearing loss – because scientists believe cellular scaffolding proteins that do not circulate or change make up hair bundles.
In a study published in the journal Cell, researchers reveal that with 15% of Americans aged 20-69 years suffering from hearing loss, manipulating how the proteins of hair bundles move via therapeutic means could reverse hearing challenges.
"What was surprising in our research with zebrafish is that proteins move so rapidly, implying that protein movement may be required to maintain the integrity of hair bundles in the inner ear," said senior author Brian McDermott, PhD, associate professor of Otolaryngology-Head and Neck Surgery, Case Western Reserve University School of Medicine.
"Our research tells us that constant movement, replacement and adjustment among proteins in the inner ear's hair bundles serve a maintenance and even repair function," McDermott added.
The researchers believe hair bundles last a lifetime because the proteins in them shift at very quick rates, a movement that was confirmed after they used confocal microscope to analyze these protein movements in real-time inside the inner ears of baby zebrafish. Since they are still very young, researchers can view the internal organs of zebrafish, including their ear structure without dissections due to their complete transparency.
"We made movies of the secret inner workings of the hair bundle in a live animal, and what is happening in the ear is amazing and unexpected," McDermott said.
The scientists noted the proteins actin and myosin move very slowly when monitored in hourly periods, while protein fascin 2b moves very fast within seconds – showing that proteins move in a very fast manner and are not stagnant, making the stereocilia dynamic.
"It was once thought that most everything within the stereocilia was relatively immobile and static," McDermott said. "We found that the constant, dynamic movement likely contributes to the permanency of the hair bundle structure to last a lifetime, or 70 to 90 years in human terms."
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The research team states that it is not clear if stereocilia heal themselves, prompting them to investigate the possibility of a repair mechanism. They disclosed that people become deaf when the stereocilia within the inner ear get damaged, but hearing loss could be healed or repaired if the proteins of the stereocilia could be therapeutically manipulated.