Learn to Love Your Folds - Anatomy of Your Voice
You have probably heard the term vocal cords used to describe the parts that are producing your voice. Sometimes you can even see an amusing, yet confused mix-up with musical terminology where someone spells them "vocal chords", which makes you wonder, are they major or minor? So chords is nonsensical, while cords is not quite accurately describing them - those cords are attached at the side as well as at each end. Only one edge of the tissue is actually exposed, thus they resemble a fold or a flap rather than a cord or string. It is for this reason the correct anatomical term is vocal folds.
Your vocal folds are housed in a structure made of several pieces of cartilage called the larynx (aka voicebox). For men, your Adam's apple is a protrusion of the largest cartilage, the thyroid cartilage. Women, you still have an Adam's apple but it is smaller and less pronounced than in men, it doesn't noticeably stick out of your neck. You may be able to feel a small triangular notch at the top part of this cartilage on your neck. Within your larynx are the two tiny parts that are your vocal folds.
If you were to stick a small camera down your throat, you would see two white bands, your vocal folds, which form a V shape, with the point coming together at your front. The space in the V between your vocal folds is called the glottis which can be open (vocal folds apart) or closed (vocal folds together). The biological purpose of the vocal folds is to provide a valve that can close off the airway, creating more pressure in the chest which can be useful for heavy lifting, excretion, and childbirth. Go ahead and pretend like you are lifting something heavy, say, a refrigerator. Act like you are going to pick it up - be sure to lift with your knees - and grunt as you pick it up and feel the weight. Notice how you hold your breath, creating pressure to help keep your torso rigid while you lift. The reason you can do this is your vocal folds come together (adduct), closing off your glottis and building pressure behind it.
The miracle of the voice is that this "air-valve", made of your vocal folds, has an auxiliary function: creating sound. By simply blowing air through the opening, the vocal folds can be forced into oscillation (vibration), producing a buzz. What happens to this buzz sound and how it becomes your voice will be covered in a later blog post about resonance. For now, lets focus on the phonation (creating the original sound) part of singing.
The vocal folds themselves are complex structures with several internal layers, including ligament and muscle. The outermost layer of the vocal folds is like a thin, gooey skin called the stratified squamous epithelium (fun vocab words) which is loose and can move independently over the the other layers, sort of like the skin on the back of your hand. This outer layer is constantly bathed in mucous that lubricates the folds and also maintains the gooey consistency of the skin. This layer has unique properties during oscillation as described below. Underneath this skin are several layers of increasing viscosity down to the main vocal muscles that make up the body of each vocal fold: the pair of thyroarytenoid muscles.
These muscles can stretch and contract, thicken and loosen, which changes the pitch and quality of the tone, much like a string. While the muscles inside behave like a string, the vocal folds as a whole also behave like a reed, pulled into oscillation by the air moving past the edges. Your brain cannot directly control the oscillation, since that is caused by airflow; your muscles on their own volition cannot vibrate fast enough (hundreds of times a second, even into the 1,000's). Instead, your brain controls the pitch (tension and length of the muscles), while oscillation is facilitated by your breath (controlled by your abdomen). The coordination of vocal fold oscillation with your breath for your vocal onset (when you begin singing) is another important topic we will cover in Part 2 of this article on vocal anatomy.
Back to the mucous and the gooey outer layer: Your voice would not have the unique sound with rich overtones that it does if your vocal folds only oscillated as a single mass. Instead, since the outer layer can slide independently over the inner layers, it produces its own set of smaller vibrations along with the larger vibrations of the whole vocal fold. If viewed in slow-motion (usually with the assistance of a strobe light) there is a visible ripple or wave-like motion up the edge of the fold.
Vocal Fold Oscillation (side cutout view)
Viewed from the side, the vocal folds can be seen as being blown open by air pressure starting at the bottom and moving to the top. Once the folds separate, the air passes through and the air pressure lowers. The lower pressure of the now moving air then sucks the bottom part of the folds back together first (look up Bernoulli's principle), then the top part, and the cycle starts again. This cycling of high and low air pressure is what makes up sound. The unique bottom-to-top, multi-level oscillation of the vocal folds is what produces the overtones that make the human voice sound unique.
Why is knowing this important? First of all, as if adequate hydration needs more justification, since the outer layer of your vocal folds is covered in mucous, it can become dried up with dehydration, breathy singing, smoking, etc., and lose the gooey and elastic properties that allows it to vibrate as described above. You may notice that when your voice feels dry, it feels stiff and sounds dull - a direct result of a lack of overtones being produced at the source. These overtones are essential to your resonance and also your ease of singing. Yes, bright resonant overtones will actually make it easier to sing, as will be explained in yet another future blog post.
Second, there is a lot of misinformation out there about how the voice works. Vocal science is relatively new: it was only within about the last 150 years or so that we were able to look inside the vocal tract of a living human, using specialized equipment, obviously. Many singers end up damaging their voices because of an incorrect conception of how their instrument functions.
With other instruments, as in, the ones external to your body, you can see them and touch them, even take them apart and look inside. All of the functionality can be directly observed. If you don't like the sound or feel of an instrument, or if it breaks, you can get a new one. Not so with the voice. All that a singer has to go on are vague, subjective sensations that may or may not accurately represent what is really going on inside. For example, many teachers advocate singing with an "open" throat. If they knew their anatomy, they would realize that there are no throat-opening muscles*, only throat-constrictors, and that any sensation of opening the throat is really just tensing up the back of the tongue and the muscles used for swallowing, generally causing the larynx to rise - not ideal for singing. The actual sensation of an unconstricted throat is of nothing at all.
I hope I have made my point and motivated readers to learn more about the anatomy of the voice. While knowledge of the voice won't replace the hours spent in the practice room refining the physical skill of singing, the broad understanding of actual scientific facts about the voice can lead to development of more accurate sensations and "mental images" of what is going on as you sing. Knowledge of the voice and how it functions will hopefully prevent the spread of well-intentioned but inaccurate methods and techniques that could lead to vocal damage or poor singing.
That's all for Part 1 of a series on vocal anatomy, I hope you all enjoyed reading! Don't forget to subscribe to be notified of new posts and please share if you found this article interesting. Thanks everyone, see you next time.
~Alexander
*with the exception of one muscle which opens the esophagus for swallowing, but this also raises the larynx and is not useful for singing.
I cannot recommend highly enough the book Your Voice: An Inside View by Scott McCoy, DMA, which taught me a lot of what I know and informs what I write about singing, especially for this post.