For the first time, scientists at the University of Wisconsin have managed to grow functional vocal cord tissue in the laboratory, in the hope that it can restore a voice to those who have lost their own vocal cords to cancer surgery or other injuries.
“Voice is a pretty amazing thing, yet we don’t give it much thought until something goes wrong,” says Welham, an associate professor of surgery in the UW School of Medicine and Public Health. “Our vocal cords are made up of special tissue that has to be flexible enough to vibrate, yet strong enough to bang together hundreds of times per second. It’s an exquisite system and a hard thing to replicate.”
To grow the vocal cords, the team took vocal cord tissue from a cadaver and four patients who had their larynxes removed. They then isolated, purified and grew the cells from the mucous membrane, before applying them to a 3D collagen scaffold.
After two weeks, the cells grew together to form tissue, and produced many of the same proteins of normal vocal cords. To test them out, the team then transplanted the bioengineered tissue into larynxes that had been removed from dogs. The larynxes were attached to artificial wind pipes and warm air was blown though them. Although not as good as the real thing, the lab-grown tissue still produced sound and had qualities of viscosity and elasticity similar to normal tissue.
How do we speak?
Vocal cords, also known as vocal folds, are situated in the larynx, which is placed at the top of the trachea. They are layers of mucous membranes that stretch across the larynx and control how air is expelled from the lungs in order to make certain sounds. The primary usage of vocal cords within humans is to communicate and it is hypothesised that human vocal cords actually developed to the extent we see now to facilitate advanced levels of communication in response to the formation of social groupings during phases of primate, and specifically human, evolution.
As air is expelled from the lungs, the vocal folds vibrate and collide to produce a range of sounds. The type of sound emitted is effected by exactly how the folds collide, move and stretch as air passes over them. An individual ‘fundamental frequency’ (their standard pitch) is determined by the length, size and tension of their vocal cords. Movement of the vocal folds is controlled by the vagus nerve, and sound is then further fine-tuned to form words and sounds that we can recognise by the larynx, tongue and lips. Fundamental frequency in males averages at 125Hz, and at 210Hz in females. Children have a higher average pitch at around 300Hz.
What’s the difference between male and female vocal chords?
Male voices are often much lower than female voices. This is primarily due to the different size of vocal folds present in each sex, with males having larger folds that create a lower pitched sound, and females having smaller folds that create a higher pitch sound. The average size for male vocal cords are between 17 and 25mm, and females are normally between 12.5 and 17.5mm. From the range in size, however, males can be seen to have quite high pitch voices, and females can have quite low pitch voices.
The other major biological difference that effects pitch is that males generally have a larger vocal tract, which can further lower the tone of their voice independent of vocal cord size. The pitch and tone of male voices has been studied in relation to sexual success, and individuals with lower voices have been seen to be more successful in reproduction. The reason proposed for this is that a lower tone voice may indicate a higher level of testosterone present in a male.
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