Transmitting sound waves to sound (Introduction)

by David Turell @, Tuesday, June 05, 2018, 19:38 (257 days ago)

We humans have an accurate complex evolved system:

https://www.scientificamerican.com/article/theres-an-inverse-piano-in-your-head/?utm_so...

"In the 19th century there was one really important physiological insight from the German scientist Hermann von Hemholtz that endures today. He recognized that the cochlea—the receptive organ of the ear—is, in essence, an inverse piano. In the piano, each of the strings represents a single tone and the output is stirred together into a harmonious whole. The ear basically undoes that work. It takes the harmonious whole, separates out the individual tones and represents each of them at a different position along the spiral cochlea. Each of the 16,000 hair cells that line the cochlea is a receptor that responds to a specific frequency. And those hair cells are in a systematic order, just as the piano strings are.

"The common currency of the nervous system is electrical. It is action potentials—streams of 1’s and 0’s, in effect—much like those in a computer. But the currency of the external sensory world is very different. We have photons—that is sight. We have pressure—that is touch. We have molecules—that is smell or taste. And finally we have vibrations in the air—that is the essence of sound. Each of those different types of physical stimulus must somehow be converted into the electrical signals that the brain is then capable of interpreting. That’s the transduction process. The thing that motivated me, and took the first 20 years of my 40-year career to really understand, is how that is accomplished. How the mechanical vibration, as it strikes the upper part of the hair cell—the so-called hair bundle—how that energy is converted into an electrical response.

"The sound going in didn’t simply evoke a response. Instead, the ear has a so-called active process. The ear has a built-in amplifier, and that amplifier is unlike any of our other senses. It would be as if light going into the eye produced more light inside the eye, or smell going into the nose produced more smell molecules. In the case of our ears, the sound that goes into the ear is actually mechanically amplified by the ear, and the amplification is between 100- and 1,000-fold. It’s quite profound. And the active process also sharpens the tuning of hearing, so that we can distinguish frequencies that are only about 0.1 percent apart. By comparison, two keys on a piano are 6 percent apart.

"One of the others is trying to understand how the hair bundle—the mechanically sensitive upper part of the hair cell—is assembled. It’s a real problem in developmental biology how you put something that complicated together. And another is the attempt to help regenerate hair cells. One of the biggest challenges in the field is that hair cells in mammals are not replaced when they die. That is why all of us tend to get progressively harder and harder of hearing, and eventually significantly deaf. One of the approaches we’re taking is to screen drugs to try to find a molecule that will allow hair cells to begin to regenerate again. We’ve screened 80,000 drugs so far and we have two compounds in particular that look promising. We’re now trying to learn in more detail how they operate, and whether they or related compounds could be used for regeneration in humans."

Comment: the complexity of the auditory system is amazing. We still don't know how the hair cells make hairs, perhaps as complexly as bacterial flagella. How did evolution develop this preciseness? Not by chance. It requires design.

Transmitting sound waves to sound

by dhw, Wednesday, June 06, 2018, 13:17 (256 days ago) @ David Turell

DAVID’s comment: the complexity of the auditory system is amazing. We still don't know how the hair cells make hairs, perhaps as complexly as bacterial flagella. How did evolution develop this preciseness? Not by chance. It requires design.

I share your amazement. You reprimanded me earlier for not responding to the post on how information is passed in cells. In most cases, I don’t respond because there is nothing to discuss, and that is also the case here. I fully accept that these complexities have not arisen by chance and require design. They represent the strongest case for the existence of a designer, but as I keep repeating – most recently in my response to reblak – the concept of a sourceless mind that creates and encompasses a universe poses just as great a strain on my credulity as that of chance or of bottom-up evolving intelligences. Nevertheless, I can only repeat how grateful I am to you for providing us with these wonderful articles, so please don’t think that a non-response means lack of attention or appreciation!

Transmitting sound waves to sound

by David Turell @, Wednesday, June 06, 2018, 15:19 (256 days ago) @ dhw

DAVID’s comment: the complexity of the auditory system is amazing. We still don't know how the hair cells make hairs, perhaps as complexly as bacterial flagella. How did evolution develop this preciseness? Not by chance. It requires design.

dhw: I share your amazement. You reprimanded me earlier for not responding to the post on how information is passed in cells. In most cases, I don’t respond because there is nothing to discuss, and that is also the case here. I fully accept that these complexities have not arisen by chance and require design. They represent the strongest case for the existence of a designer, but as I keep repeating – most recently in my response to reblak – the concept of a sourceless mind that creates and encompasses a universe poses just as great a strain on my credulity as that of chance or of bottom-up evolving intelligences. Nevertheless, I can only repeat how grateful I am to you for providing us with these wonderful articles, so please don’t think that a non-response means lack of attention or appreciation!

An excellent description of your dilemma and thank you.

Transmitting sound waves to sound; Tectorial membrane

by David Turell @, Sunday, February 17, 2019, 20:45 (54 minutes ago) @ David Turell

A very delicate gelatinous membrane does the trick:

https://www.livescience.com/64781-jello-membrane-tunes-your-ear.html?utm_source=ls-news...

"This optical microscope image illustrates wave motion in the tectorial membrane, a gooey membrane somewhat reminiscent of Jell-O that sits on top of the sensory hair cells in the cochlea. New research shows that the membrane is able to tune its stiffness to better translate sounds at certain frequencies into neural impulses.

"In order to turn tangled, airborne vibrations into recognizable sounds, your ear relies on a miniature assembly line of bones, fibers, tissues and nerves. Then, there's the "Jell-O."

There's no actual gelatin in your ears, of course (if you're doing hygiene right). But according to Jonathan Sellon, a visiting professor at MIT and lead author of a new study in the journal Physical Review Letters, there is a thin, "Jell-O-like" blob of tissue spiraling through your inner ear and helping sound waves reach the specific nerve receptors they need to in order to make contact with your brain. This helpful blob is known as the tectorial membrane.

"'The tectorial membrane is a gelatinous tissue that's made up of 97 percent water," Sellon told Live Science. "And it sits on top of the tiny sensory receptors in the inner ear (or cochlea) that translate sound waves into an electrical signal that your brain can interpret."

"So, why cover your ears' hypersensitive sound-pickup equipment with a layer of Jell-O? Sellon wanted to know when he began researching the tectorial membrane eight years ago. Now, in their new study (published Jan. 16), he and his colleagues think they may be on to an answer.

"With their tips poking into the membrane's gooey innards, the inner ear's sensory receptor cells (also known as "hair cells") run in bundles across the length of your cochlea, each one built to respond best to a different range of frequencies; high frequencies are best translated by cells at the base of the cochlea, while low frequencies amplify best at the top of the cochlea. Together, these hairy receptors allow you to hear thousands of different frequencies of sound.

"'The tectorial membrane actually helps the cochlea separate out low-frequency sounds from high- frequency sounds," Sellon said. "The way it does that is by 'tuning' its own stiffness, sort of like the strings on an instrument."

***

In general, the gel appeared stiffer near the base of the cochlea, where high frequencies are picked up, and less stiff in the apex of the cochlea, where low frequencies register. It's almost as if the membrane itself was dynamically tuning itself" like a musical instrument, Sellon said.

"'It's kind of like a guitar or violin," Sellon said, "where you can tune the strings to be more or less stiff depending on the frequency you're trying to play."

"How exactly does this Jell-O tune itself?

"It turns out that water flows through microscopic pores inside the membrane. The pore arrangement changes how fluid moves through the membrane — thereby changing its stiffness and viscosity at different locations in response to vibrations.

"This tiny Jell-O guitar might be critical for amplifying certain frequency vibrations at different positions along the cochlea, Sellon said, helping your ears optimize the conversion of sound waves from mechanical vibrations to neural impulses.

"The pore arrangement allows hair cells to respond more efficiently to the middle range of frequencies — for example, those used for human speech — compared to sounds at the low and high ends of the spectrum. So, sound waves in those middle ranges are more likely to be converted into distinct neural signals, Sellon said.

"The membrane's sensitivity might even serve as a natural filter that helps amplify faint sounds while dampening distracting noise — however, Sellon said, further research in living subjects is needed to better understand all the membrane's mysteries."

Comment: Fascinatingly complex. I can understand the jello comparison. If you've ever made
jello note how it vibrates in waves if shaken. This evolved long before humans, but is so complex, it had to be designed as a complete organ all at once.

RSS Feed of thread
powered by my little forum