One membrane, many frequencies

March 27, 2007

Modern hearing aids, though quite sophisticated, still do not faithfully reproduce sound as hearing people perceive it. New findings at the Weizmann Institute of Science shed light on a crucial mechanism for discerning different sound frequencies and thus may have implications for the design of better hearing aids.

Research by Dr. Itay Rousso of the Weizmann Institute’s Structural Biology Department, which recently appeared in the Proceedings of the National Academy of Sciences, suggests that a thin structure in the inner ear called the tectorial membrane responds to different frequencies. This membrane communicates between the outer hair cells (which amplify sound in the form of mechanical vibrations) and the inner hair cells (which convert these mechanical vibrations to electrical signals and pass them on to the brain via the auditory nerve). If certain genes for this membrane are missing or damaged, total deafness ensues.

Rousso and research student Rachel Gueta, together with researchers at the Ben-Gurion University of the Negev, wanted to explore the mechanical properties of the tectorial membrane. Using an atomic force microscope, which probes surfaces with a fine microscopic needle, they tested the resistance of the gel-like membrane at various points to assess precisely how rigid or flexible it was. To their surprise, the scientists found that the level of rigidity varies significantly along the length of the membrane: One end of the membrane can be up to ten times more rigid than the other.

These differences occur in the part of the membrane that is in direct contact with the outer hair cells. Observation under a scanning electron microscope revealed that this variation is due to changes in the way the protein fibers are arranged: At one end, they form a flimsy, net-like structure that allows the membrane to be flexible; on the rigid side, the fibers are densely and uniformly packed.

The more rigid a tectorial membrane is, the higher the frequency at which it can vibrate. Thus, the flexible end of the membrane, which should respond to low-frequency vibration, is found near the hair cells that transmit low frequencies, and the rigid end near hair cells that transmit high ones. This spatial separation, say the scientists, translates into the ability to distinguish between sounds of different frequencies.

The new understanding of the mechanics of hearing may assist in the development of better hearing aids. Rousso, meanwhile, plans to continue exploring how variations in membrane rigidity affect hearing. He intends to test tectorial membranes under different physiological conditions to further understand how we hear such a wide range of frequencies (the highest is a thousand times the lowest), as well as to shed light on the causes of certain hearing problems.

Source: American Committee for the Weizmann Institute of Science


Rank 5 /5 (2 votes)
Tags

Relevant PhysicsForums posts

More news stories

Entire genome of extinct human decoded from fossil

(PhysOrg.com) -- In 2010, Svante Pääbo and his colleagues presented a draft version of the genome from a small fragment of a human finger bone discovered in Denisova Cave in southern Siberia. The ...

Biology / Biotechnology

created Feb 07, 2012 | popularity 4.7 / 5 (57) | comments 43 | with audio podcast

Why are there so few fish in the Earth's oceans?

(PhysOrg.com) -- A Stony Brook University researcher has found that, contrary to popular belief, there are not plenty of fish in the sea.

Biology / Plants & Animals

created Feb 08, 2012 | popularity 4.3 / 5 (15) | comments 25 | with audio podcast

The power of estrogen -- male snakes attract other males

A new study has shown that boosting the estrogen levels of male garter snakes causes them to secrete the same pheromones that females use to attract suitors, and turned the males into just about the sexiest ...

Biology / Plants & Animals

created Feb 10, 2012 | popularity 4.8 / 5 (6) | comments 2 | with audio podcast

Miami battling invasion of giant African snails

No one knows how they got there. But an invasion of African giant snails has southern Florida in a panic over potential crop damage, disease and general yuckiness surrounding the slimy gastropods.

Biology / Ecology

created Feb 10, 2012 | popularity 4.5 / 5 (2) | comments 5

Deciding to go left or right: Researchers use device to determine that lower animals can navigate too

For decades, scientists have associated binary decision making — opting to go left or right — with higher-ranking animals, including humans. A team of Harvard researchers, however, is rewriting that ...

Biology / Plants & Animals

created Feb 09, 2012 | popularity 4 / 5 (1) | comments 4 | with audio podcast


Walney offshore wind farm is world's biggest (for now)

(PhysOrg.com) -- The Walney wind farm on the Irish Sea--characterized by high tides, waves and windy weather--officially opened this week. The farm is treated in the press as a very big deal as the Walney ...

GPS court ruling leaves US phone tracking unclear

A US Supreme Court decision requiring a warrant to place a GPS device on the car of a criminal suspect leaves unresolved the bigger issue of police tracking using mobile phones, legal experts say.

Study finds that anti-diabetic medication can prevent the long-term effects of maternal obesity

In a study to be presented today at the Society for Maternal-Fetal Medicine's annual meeting, The Pregnancy Meeting, in Dallas, Texas, researchers will report findings that show that short therapy with the anti-diabetic medication ...

Europe stakes billion-dollar bet on new rocket

A pencil-slim rocket is scheduled to lift into space from South America on Monday, carrying a billion-dollar bet that Europe can grab a juicy slice of the market to place satellites in low orbit.

Netflix settlement trims 14 pct off 4Q earnings

(AP) -- Netflix pressed the rewind button on its fourth-quarter earnings after settling allegations that the video subscription service violated a consumer-privacy law.

Europeans protest controversial Internet pact

Tens of thousands of people marched in protests in more than a dozen European cities Saturday against a controversial anti-online piracy pact that critics say could curtail Internet freedom.