May 12, 2015 | David F. Coppedge

The Parts List for Hearing

Want to hear what goes on when you hear sounds? Hair cells wave in the fluid, responding to specific frequencies, and hundreds of proteins go into action.

Talk about splitting hairs. Harvard Medical School begins a press release with some gee-whiz facts about the hair cells involved in hearing:

Amazing FactsFor balance, five separate patches of hair cells sense movement and tell the brain where the head is in space while translating the pull of gravity.

For hearing, a five cell-wide ribbon of 16,000 hair cells spirals inside the cochlea, the snail-shaped structure where hair cells vibrate in response to sound waves. Every cycle of sound waves sends microscopic cilia on the tips of these cells back and forth, riding a trampoline of cells suspended between two fluid-filled spaces.

The movement opens pores in the cells, allowing electrical current to flow inside.  This conversion of mechanical to electrical signals sends nerve impulses to the brain, which then “hears” the sound.

In their efforts to understand the causes of hereditary deafness, researchers at HMS have tried to first identify a “parts list” of players. Working with mice, they have identified about 300 genes involved in hearing so far, but they think only one-third of proteins are known.

The cutaway diagram of a cochlea in the article looks like a highly structured, well-organized array of cells. (Image: Courtesy of Nelson Kiang, MEE). The hair cells are colored green. This array, resembling the keyboard of a pipe organ, tapers in the coils of the cochlea, with each rank of hair cells responding to specific frequencies.

Hair cells (green) inside the cochlea in the inner ear vibrate with sound waves. Image: Courtesy of Nelson Kiang, MEE

 

Make Like a Bat

If you have good high-frequency hearing, you can use echoes to “see” your way around with sound, like a bat does. Researchers at the University of Southampton found that the high-frequency response gives the best results. This is a way blind people can compensate for loss of sight by leveraging the precision audio response of the ears.

Bats, like dolphins, use biosonar for locating food. A paper in PNAS describes how they adjust the gape of their mouth to act as a zoom lens when they emit clicks. The prey have their ways for fighting back. Another paper in PNAS says that hawkmoths emit ultrasound to “jam” the bats’ sonar. The article claims that this jamming ability evolved separately two times in the moths.

Update 5/13/15: Science Daily says that eardrums evolved independently in mammals and reptiles/birds; “convergent evolution can often result in structures that resemble each other so much that they appear to be homologous,” the evolutionist says.

Ignore the evolutionary stories (good grief, convergent evolution again). Focus on the main thing: Ears are amazingly intricate organs. Talk about irreducible complexity! Imagine Darwinian luck getting even two proteins to work together, let alone 300 to a thousand. Look at the illustration. As elegant and lovely as it is, it would be useless without an even more complex brain able to receive the electrical impulses and interpret them.

Things this complex, with such high performance specifications, do NOT just happen. The design is so over-the-top beautiful and functional, why do we even pay attention to mere humans who make up stories, saying it evolved? Get real; get intelligent design science.

 

Image: Courtesy of Nelson Kiang, MEE

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