Anatomy and Physiology Series: Laryngeal Physiology (Part 2, muscular coordination)

In my last A&P post, I went over the air pressure laws that keep the vocal folds in motion during phonation.  Now, we're going to go over the muscular effort required in changing the pitch and volume of the voice in general.

There's one thing very basic to the muscular process of phonation to understand:  It is only the onset of phonation where active muscular contraction is required.  During sustained voicing, the adductors are being held in position by background muscle tone, which is regulated by the information the sensory nerves of the muscle spindles send to the central nervous system.  So the continuous vibration of the vocal folds is a result of subglottal, intraglottal, and supraglottal air pressure/air flow and the physical shape of the glottis from the vocal fold properties and not from repeated adducting/abducting of the musculature.  Also, your folds need not be completely adducted in order for voicing to occur, although that usually results in a slightly (not abnormally) "breathy sound."  So onset is all about the active contraction of the adductors moving simultaneously to close the glottis.*

Now, the ideal adductor position for phonation would involve the minimal contact needed to maintain the minimum driving pressure, 3-5 cm H2O, of the vocal folds.  (Typically, this results in a vocal volume of comfortable, conversational speech.)  If a person goes past that ideal by increasing medial compression to an uncomfortable amount, pressed phonation occurs.  Pressed phonation increases the volume of the voice, but also tends to have a harsh sound quality, like someone shouting.  (This is pretty much the equivalent to "pushing" the voice in singer-language.)  Breathy phonation is the opposite of pressed, resulting from inadequate closure allowing too much air to escape during the closed phase of the vibratory cycle.  It can be a sign something is wrong or it can just be when you're trying to speak softly, like in a library or something. In solo singing, excessive breathiness it can also be a sign of inefficient coordination or it could be due to age in that young voices are naturally more breathy.  (Important take-away here for teachers:  Don't jump to "diagnose" a voice disorder from breathiness alone, refer the student to an ENT if you're concerned.)*


I think we should certainly go over pitch change in the voice to better understand the coordination that singing requires throughout the vocal range.  Most students of pedagogy know that pitch change occurs from the cricothyroid and thyrovocalis muscles stretching and tensing the vocal folds.  But why does that change the pitch?  It all comes back to physics, yet again.  It works the same way tightening a violin string works:  Increasing tension and decreasing the mass results in a higher fundamental frequency for that string.  Now, we don't actually change the overall mass of the vocal folds.  But we do change the mass per unit length by stretching them out over a greater distance.  This is called the effective mass of the vocal folds--or the mass that's actually making contact during vibration.  If a body has more mass, it will vibrate at a slower rate, resulting in a lower frequency.  If we decrease the mass per unit by increasing the distance (stretching the folds,) the vibration will be faster, which will result in a higher pitch.* 

Here's where things start to get messy for us singers:  Increased subglottal pressure typically results in increased vocal fold contact time during each vibration and complete glottal closure during vibration.  This results in a louder voice (or higher amplitude sound waves).  Because increasing pitch increases the tension of the folds, the vocal fold edges don't normally completely meet up at extreme ranges, resulting in that falsetto sound we all know so well.  If you want to maintain vocal loudness at extreme ranges, it could be through increased vocal fold contact during vibration and thus maintained subglottal pressure like when you were lower, or you could create the impression of maintained vocal loudness by shaping the vocal tract such that certain harmonics get an amplitude "boost" without having to actually increase vocal fold contact.  The tricky thing to figure out as a classical singer is when you are voicing loudly in an efficient way and when you are "pushing"--where you're really on the verge of screaming.  Most advanced singers I know mentally consider their loudest dynamic to be mentally within their "normal inside voice" speaking loudness.  That would require a lot of resonance work to balance out and still produce a professional sound that travels, but it does explain why so many of the greatest singers look like they're just hanging out with their mouths open on high, loud notes.  It's likely that advanced singers use a variety of these coordinations in their high ranges to produce various dynamics.  It's also likely that figuring out the ideal coordination on high notes is very individual, involving an intricate, flexible coordination of the respiratory system to the laryngeal system to the vocal tract such that different vocal colors and dynamics can be achieved.  So, if it took you a long time to "master" resonance and dynamic contrasts throughout your range, you're not alone!  It's the hardest and most complicated thing to master as the "how to" is so very individual--and receiving guidance requires a teacher with both the skill to explain things well and the ear to hear professional-level resonance/vocal balance versus vocal strain.  (Let's face it, a lot of amazing voices out there can still produce pretty good sound when they're straining.  The issue with this is they might not be able to sustain that throughout a career and it puts them at higher risk for voice injury in the future.  I see just as many classical singers "push" as belters out there and just as many well-balanced, unstrained singers in both genres, so singing "classically" does not in itself "protect you" from strain.)

Now, when we speak, we're changing the pitch and loudness of our voice all the time with our inflections, so these changes occur waaaayyy in the background of our conscious mind.  Where this becomes an issue in singing, I believe, is when we consciously train this correct balance of muscular tension, adduction, and subglottal pressure as we move well outside of our daily speaking range.  I believe the correct coordination requires training the proper balance of subglottal pressure throughout the range. The ideal balance will result in the unconscious coordination of subglottal pressure with medial compression up and down the whole vocal range.  When this coordination is relegated to the background functions of our brain, it tends to be the most efficient and therefore, it feels as though you're doing "nothing" to sing the way you do.


I feel, as a singer and a teacher, that we have a tendency to keep this coordination under our conscious control for far longer than we should, which does result in inefficiency since the conscious portion of our brain is not the best equipped to maintain fine-motor coordination.  Conscious muscular training is a pretty quick process, and once that is completed, it is time to allow the body to discover the proper coordination without encouraging our "control" over it, which requires an attitude of educated play and discovery rather than control or "right and wrong."


I feel I would be remiss in not mentioning a little about the extrinsic musculature here.  The extrinsic musculature can make adjustments to the laryngeal posture--raising it or lowering it.  The larynx tends to rise in coordination with an increase in pitch in untrained individuals.  The muscles that elevate the larynx are usually coordinated to the pharyngeal muscles that constrict the vocal tract.  This coordination is really, really important when we swallow, but we don't really want it to activate when we sing.  If you're painfully aware of those raising or lowering adjustments in the form of neck tension, the coordination at the fold-level is very likely compromised and inefficient.

(Updated: 08/23/2015)  


*Seikel, J. A., King, D. W., & Drumright, D. G. (2010). Anatomy and physiology for speech, language, and hearing. Clifton Park, NY: Delmar.