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Biology Articles » Anatomy & Physiology » Vocal cords deserve the applause

Vocal cords deserve the applause

The vocal cords are twin folds of throat muscle stretched horizontally across the voice box, or larynx. When breathing, air passes through an opening between them. To make sound, they're drawn together. They vibrate when air is forced past them, much as a reed vibrates in a flute.

For such a simple construction, vocal cords are capable of an astonishingly wide variety of sounds: the arias of Maria Callas, the wrenching vibrato of Edith Piaf, inarticulate moans and screams, and everyday conversation with the speaker's characteristic lilt and accent. Pitch rises or falls depending on how tautly the cords are stretched ---- think of the strings in a guitar. Volume is regulated by the force of air expelled past the cords.

Vocalizing isn't just a physical act. It's a finely honed cooperative production of the brain's speech center, nerves that carry its signals to the cords, head, neck, chest and abdomen. Learning these intricate skills takes years, as anyone who has raised a child knows.


Adults are reminded of the intricacies of speech when they develop voice problems. Laryngitis, an inflammation of the larynx and vocal cords, can make one's voice so hoarse it's scarcely recognizable, or make vocalization impossible. This usually lasts no longer than a couple of weeks.

Laryngitis is an inflammation of the larynx and vocal cords. The inflammation makes the tissues rough and irregular, so the vocal cords can't snap shut and open in their usual clean, precise manner. It's often accompanied by a tickling sensation, a need to clear one's throat, or a sore, raw-feeling throat.

Viral infections such as colds are the most common causes of laryngitis. Rest and time is the usual treatment in such cases, though prolonged loss of voice indicates a more serious problem.

Hoarseness or loss of voice can also be caused by tobacco smoke and alcohol, along with damage from stomach acid surging into the throat, a condition called gastroesophageal reflux disease (GERD).

Less commonly, growths on the vocal cords can make speech difficult or impossible. Pete Wilson, former San Diego mayor, suffered from this condition in 1995, when he was running for president. Wilson required surgery to remove the noncancerous growths. While the surgery was successful, Wilson's voice was out of commission for two months ---- a major handicap for any politician.

More lasting damage to speech ability can occur from stroke or nerve damage. If the nerve impulses that signal the vocal cords to move together are blocked, speech is impossible. Prosthetic devices can restore voice to such patients. They need to relearn how to talk, because nerves and muscles must be trained to work with the prosthesis.

In 1998, the U.S. Food and Drug Administration approved implants designed by doctors at Johns Hopkins School of Medicine. The implants push the vocal cords to the center, enabling them to meet and make sound.

In cases where the larynx has been removed because of cancer, it's necessary to create an artificial vocal cord. That has traditionally been done by placing a silicone flap against the windpipe and esophagus. The flap vibrates between them, making sound. However, the voice so created often sounds "gruff," and low pitched, especially disturbing to female speakers.

In 2005, Dutch scientists reported they had made a different kind of implant that makes a more normal-sounding voice. The implant makes sound on its own, because it contains an internal flap that vibrates against the valve. Different flaps were constructed to produce male and female voices. The research was performed by Marein van der Torn and colleagues at the University of Groningen. So far, it appears that only female patients with a weak voice will benefit from the delicate prosthesis.


 

Source: NCTimes.com, July 29, 2006


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