Stereocilia, or the tiny hairs inside our ears, are an integral part of the hearing system. But overexposure to noise - such as experienced in music concerts or blasting tunes from an iPod - can permanently damage them, degrading a person's hearing over time. Researchers at Stanford, however, have hit a breakthrough in growing hair-like cells that function just like those in our ears. This could mean solutions for damaged hearing.
Gizmag writes, "[W]e’re born with 30,000 [stereocilia] per ear, but once they die off or get damaged, they’re gone for good. Stefan Heller, a professor of otolaryngology (ear, nose and throat) at Stanford University, wants to change that. To that end, he recently succeeded in creating mouse hair cells in a petri dish. Could an end to deafness be far behind?"
How Hairs In Our Ears Help Us Hear
From the National Institute of Deafness and other Communication Disorders, here's how our hearing works:
Sound waves enter the outer ear and travel through a narrow passageway called the ear canal, which leads to the eardrum. The eardrum vibrates from the incoming sound waves and sends these vibrations to three tiny bones in the middle ear. These bones are called the malleus, incus, and stapes. The bones in the middle ear amplify, or increase, the sound vibrations and send them to the inner ear—also called the cochlea—which is shaped like a snail and is filled with fluid. An elastic membrane runs from the beginning to the end of the cochlea, splitting it into an upper and lower part. This membrane is called the “basilar” membrane because it serves as the base, or ground floor, on which key hearing structures sit. The sound vibrations cause the fluid inside the cochlea to ripple, and a traveling wave forms along the basilar membrane. Hair cells—sensory cells sitting on top of the membrane—“ride the wave.”
As the hair cells move up and down, their bristly structures bump up against an overlying membrane and tilt to one side. This tilting action causes pore-like channels, which are on the surface of the bristles, to open up. When that happens, certain chemicals rush in, creating an electrical signal. The auditory nerve carries this electrical signal to the brain, which translates it into a “sound” that we recognize and understand.
Hair cells near the base of the cochlea detect higher-pitched sounds, such as a cell phone ringing. Those nearer the apex, or centermost point, detect lower-pitched sounds, such as a large dog barking.
So, as hair cells break down, so too does our ability to hear. The new research done at Stanford university to regrow hair cells could be a boon for those suffering from noise induced hearing loss.
Growing Hairs in a Petri Dish Could Mean Cures for Deafness
While it could indeed be an aid for correcting hearing loss, it will be a while before we see this implanted in people. Just getting hair-like cells to grow in a petri dish has been a 10-year process.
Described in an article published in Cell, Heller and team used embryonic stem cells and fibroblasts from mice and engineered them into cells that look and perform like hair cells. By mimicking the steps that occur during the formation of a mouse's ear in utero, the team created ear cells, and altered the "chemical soup" in the petri dish so the cells cluster like hair cells, which also formed stereocilia. The stereocilia are what bend with vibrations to create electrochemical signals that our brain interprets as sound. When subjected to tests, the researchers found that the synthesized sterocilia functioned exactly as they should, producing the electrochemical current needed for sound.
“We knew it was really working when we saw them in the electron microscope,” Heller said. “They really looked like they were more or less taken out of the ear.”
It will be another decade or so, however, until we see this research put into use in humans. Additionally, this seems to be a solution for noise-induced hearing loss. However there are many forms of deafness that don't include the stereocilia, so this is a potentially great solution for some, but not a catch-all cure for all.
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