Day 11: Inside the Vocal Folds
VoSci Academy – Structure Meets Function
Today we step back from exercises to study what’s doing the work: the true vocal folds. If you want to train your voice with intention, you need to know what you’re actually training. And that means understanding both the structure and the function of the vocal folds.
The 5-Layer Structure of the True Vocal Folds
The true vocal folds (sometimes called “vocal cords”—an outdated and anatomically misleading term) aren’t strings or flaps—they’re highly specialized muscular structures made for both vibration and closure. The current best anatomical model breaks them into five distinct layers:
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Epithelium
The outermost layer—a thin, pliable cover. It’s like skin, but more delicate. This layer helps the folds oscillate smoothly. -
Superficial Layer of the Lamina Propria
Often called Reinke’s Space, this gel-like layer acts like a cushion. It’s responsible for much of the vocal fold’s wave-like motion during phonation. -
Intermediate Layer of the Lamina Propria
Made of elastic fibers. It gives the fold its stretch and flexibility. -
Deep Layer of the Lamina Propria
Made of collagen fibers. Stronger, denser, and more rigid. -
Thyroarytenoid (TA) Muscle
The innermost layer, and the bulk of the fold. It actively shortens and thickens the fold when engaged.
Each of these layers contributes differently to vibration and pitch control. The outer layers move more freely and with less resistance, while the deeper layers offer strength and mass.
Function: TA vs. CT Activation
Two primary muscle groups control pitch and registration:
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Thyroarytenoid (TA) muscles: Shorten and thicken the folds. Dominant in chest voice.
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Cricothyroid (CT) muscles: Stretch and thin the folds. Dominant in head voice.
Most singers think of chest and head voice as opposites. Anatomically, that’s not true. These systems are complementary. Nearly every sound you make involves some contribution from both.
Even in what feels like pure chest voice, your CTs are contributing subtle tension. Even in soft falsetto, your TAs may not fully turn off. The idea of mix voice isn’t just stylistic—it’s anatomical reality.
How the Folds Produce Sound
Sound production happens when the vocal folds rapidly open and close, hundreds of times per second, creating pulses of air that form the basis of pitch. This process is called phonation, and it happens at a rate that matches the fundamental frequency of the note you’re singing.
For example, if you sing A4 (440 Hz), your vocal folds open and close 440 times per second. That vibratory pattern is what defines pitch.
But here’s the critical part: you can’t simply choose a frequency like pressing the A key on a piano. Producing accurate pitch is a trained coordination between your nervous system, breath pressure, and the muscular tension of the folds. It’s learned, not commanded.
And yes—the folds themselves are what’s making the sound. But it’s not the final product yet. The raw acoustic pulses still need to be shaped by resonance to become what we recognize as the singing voice.
Breath Pressure and the Phonation Threshold
For phonation to happen, there must be enough subglottal pressure—air pressure below the vocal folds—to push them open. But it can’t be too much:
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Too little pressure = no sound
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Too much pressure = instability, cracking, or pressed tone
This balance point is known as the phonation threshold pressure—the minimum amount of breath pressure needed to initiate and sustain vibration.
That’s exactly what the VFEs from Day 9 are training: how to find and sustain efficient vibration with minimal excess force. They gently condition the folds to respond to low-pressure, high-efficiency airflow.
How This Shapes Your Training
Where a singer spends most of their time—vocally and conversationally—affects muscular balance. In the United States and many other places, most people speak very low in their range, using TA-dominant production throughout the day. This builds strength in the TA muscles but leaves the CT muscles comparatively underdeveloped.
That imbalance creates real problems in the singing voice:
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Transition trouble through the middle (what some call the “break”)
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Weak or breathy-sounding high notes
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Over-reliance on mass rather than stretch
Exercises like the Day 9 VFEs can help correct this. Sustained, soft phonation encourages the CT muscles to activate and build coordination. Over time, this strengthens the system that controls pitch elevation and allows more fluid shifts between vocal registers.
You’re not just learning what to do—you’re learning why it works. And that makes your training more focused, more efficient, and ultimately more effective.
Key Takeaways
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The vocal folds have a complex 5-layer structure designed for precise control and efficient vibration.
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TA muscles (chest voice) and CT muscles (head voice) function in tandem, not in isolation.
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There is no clean split between registers; nearly all sounds are a blend of TA and CT involvement.
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Most people overuse TA and undertrain CT in everyday life—contributing to vocal imbalance.
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Phonation requires a delicate balance of subglottal pressure: not too little, not too much.
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Exercises like the VFEs help strengthen CT gently and build better coordination across the system.
Reminder: Keep practicing and recording your Day 9 VFEs.
They remain a cornerstone of your vocal development—building the coordination and pressure balance that today’s anatomy explains.
Coming Up: Messa di Voce
Tomorrow, we move from theory to sensation. You’ll learn how to physically explore the extremes of TA- and CT-dominant production using controlled swells—what singers call messa di voce. It’s one of the clearest windows into your real-time vocal function.
