Physiology of Phonation: Voice Production and Neural Control
Phonation is the production of sound by vibration of the vocal folds as expiratory air passes through the larynx. Speech then modifies this sound through resonance and articulation in the pharynx, mouth and nose.
Breath power → vocal-fold vibration → resonance → articulation. Normal voice requires coordinated respiratory support, mobile vocal folds, intact sensation and precise neural control.
Learning objectives
- Explain the myoelastic-aerodynamic theory of phonation.
- Describe control of pitch, loudness and quality.
- Outline laryngeal nerve supply.
- Assess common causes of dysphonia.
Prerequisites for normal voice
Expiratory airflow and subglottic pressure provide the energy source.
Adducted vocal folds convert steady airflow into sound pulses.
Pharyngeal, oral and nasal cavities shape the acoustic signal.
Tongue, lips, palate, jaw and teeth turn sound into intelligible language.
Myoelastic-aerodynamic theory
- The vocal folds move toward the midline before phonation.
- Expiratory muscles raise subglottic pressure.
- Air pressure overcomes resistance and separates the inferior fold margins.
- Elastic recoil plus changing airflow pressure brings the folds together again.
- Rapid repeated opening and closing creates periodic air pulses perceived as sound.
The mucosal cover moves over the deeper vocal ligament and muscle, producing the mucosal wave. A stiff lesion such as scar or some tumours reduces this wave.
Control of vocal-fold position
| Muscle | Voice function |
|---|---|
| Posterior cricoarytenoid | Abducts folds for breathing. |
| Lateral cricoarytenoid and interarytenoids | Adduct folds for phonation and airway closure. |
| Cricothyroid | Lengthens and tenses folds, usually increasing pitch. |
| Thyroarytenoid/vocalis | Shortens, relaxes and fine-tunes tension and glottic closure. |
Pitch, loudness and quality
- Pitch depends mainly on vibration frequency. Longer, thicker or less tense folds vibrate more slowly; increased tension generally raises pitch.
- Loudness increases with greater subglottic pressure and efficient glottic closure.
- Quality reflects fold symmetry, closure pattern, mucosal pliability and resonant filtering.
- Registers are patterns of vibration used across pitch ranges, including modal and falsetto-type production.
Pubertal laryngeal growth lengthens the vocal folds, particularly in males, and lowers habitual pitch.
Resonance and articulation
The sound created at the glottis contains many frequencies. The vocal tract selectively amplifies some frequencies, creating formants that shape voice identity and vowels. The soft palate regulates nasal resonance. Excess nasal airflow causes hypernasality; insufficient nasal resonance causes hyponasality. Articulators generate consonants and precise speech.
Neural control
Motor planning involves cortical speech and motor networks, basal ganglia, cerebellum and brainstem. The vagus supplies the larynx:
- The recurrent laryngeal nerve supplies all intrinsic muscles except cricothyroid.
- The external laryngeal nerve supplies cricothyroid.
- The internal laryngeal nerve provides sensation above the folds; recurrent laryngeal sensory fibres serve below.
Breath control depends on respiratory centres and spinal motor output; articulation additionally recruits CN V, VII, IX and XII.
Clinical assessment of voice
- History: onset, duration, vocal demand, pain, reflux symptoms, smoking, surgery, intubation and neurological disease.
- Perceptual description: roughness, breathiness, strain, pitch and loudness.
- Examine mouth, neck, cranial nerves and respiratory function.
- Visualise the larynx; videostroboscopy can assess mucosal-wave behaviour.
- Acoustic and aerodynamic measures may quantify selected abnormalities.
Persistent hoarseness, especially with smoking history, neck mass, dysphagia, haemoptysis, stridor or weight loss, requires laryngeal visualisation and timely ENT assessment.
Common disturbances
| Problem | Mechanism or clue |
|---|---|
| Laryngitis | Inflammation alters mass and vibration, producing hoarseness. |
| Vocal nodules/polyps | Phonotrauma produces focal lesions and an irregular mucosal wave. |
| Recurrent laryngeal palsy | Weak or immobile fold causes breathy voice or airway problems. |
| Spasmodic dysphonia | Task-specific laryngeal dystonia causes breaks and strained or breathy speech. |
| Malignancy | Persistent progressive dysphonia; risk increased by tobacco and alcohol. |
Voice-care principles
- Adequate hydration and avoidance of smoke.
- Avoid shouting, prolonged whispering and repeated throat clearing.
- Treat the identified cause rather than empiric prolonged medication.
- Voice therapy may improve technique and reduce harmful vocal behaviours.
Review the anatomy of the larynx and laryngitis.
Key examination points
- Airflow supplies power; vocal-fold vibration creates the source sound.
- Resonance and articulation shape that sound into speech.
- Pitch depends on fold length, mass and tension.
- Cricothyroid is supplied by the external laryngeal nerve.
- Persistent hoarseness must not be dismissed without visual assessment.
References and further reading
- NCBI Bookshelf: Larynx Vocal Cords.
- NCBI Bookshelf: Laryngeal Muscles.
- NCBI Bookshelf: Anatomy of the Larynx.
For education only. Apply current Uganda Clinical Guidelines, local protocols and specialist advice.
