Physiology of Speech and Swallowing

Speech: Phonation & Respiration - Voice Box Virtuoso

Voice: interplay of respiration (power) & laryngeal phonation (source).

• Respiration (Power):

  • Lungs: airflow. Subglottic pressure ($P_{sub}$) builds under adducted VFs.
  • $P_{sub}$ overcomes VF resistance → vibration.

• Phonation (Source - Larynx):

  • Vocal Folds (VFs): Vibrate for sound.
    • Layers: Epithelium, Lamina Propria (S, I, D - Reinke's in S), Vocalis m. 📌 ELSI-DV.
    • Glottis: Space between VFs.
  • Mechanism: Myoelastic-Aerodynamic Theory
    • Myoelastic: VF adduction, elasticity, tension.
    • Aerodynamic: Airflow + Bernoulli effect (↓pressure at constriction → VF closure).
  • F0 (pitch): Male 85-180 Hz; Female 165-255 Hz.

⭐ RLN innervates all intrinsic laryngeal muscles except cricothyroid (by SLN-external). RLN palsy → VF paralysis.

Speech: Articulation & Resonance - Sound Shapers

Articulation shapes phonated sound using articulators. Resonance modifies sound via vocal tract cavities.

• Articulators: Modify airstream.

  Articulator	Role / Sounds
  Lips	Bilabials (p, b, m), rounding
  Tongue	Vowels, consonants (t, d, k, g)
  Teeth	Dentals (th), labiodentals (f, v)
  Hard Palate	Palatals (sh, y)
  Soft Palate (Velum)	Velars (k, g, ng), VP closure

• Resonating Cavities: Pharyngeal, Oral, Nasal. Nasal cavity for /m/, /n/, /ŋ/.
• Velopharyngeal (VP) Closure: Seals nasal from oral cavity for non-nasal sounds. Incomplete → hypernasality.
• Formants: Vocal tract resonant frequencies; define vowels (key: F1, F2).

⭐ Failure of velopharyngeal closure leads to hypernasal speech (rhinolalia aperta) and can be assessed by tests like the mirror test or nasometry.

Swallowing: Phases & Protection - The Safe Swallow

• Phases of Swallowing (📌 Oh Please Eat: Oral, Pharyngeal, Esophageal)

  • Oral Preparatory (Voluntary): Bolus formation (mastication, saliva); sensory input.
  • Oral Transit (Voluntary): Tongue propels bolus posteriorly; triggers pharyngeal phase. < 1-1.5 sec.
  • Pharyngeal (Involuntary, Rapid): Reflex from oropharynx to UES. Airway protected. < 1 sec.

    ⭐ Pharyngeal phase: involuntary, rapid (< 1 sec). Complex neuromuscular coordination ensures bolus propulsion into esophagus while protecting airway. Impairment leads to aspiration risk.

  • Esophageal (Involuntary): Peristalsis (UES to LES); LES relaxes for stomach entry. 8-20 sec.

• Airway Protection (Pharyngeal Phase - "Safe Swallow"):

  • Velopharyngeal seal (soft palate elevation).
  • Laryngeal elevation & anterior pull (hyolaryngeal excursion).
  • Epiglottic retroflexion (covers laryngeal inlet).
  • Laryngeal closure:
    • True vocal cord adduction.
    • False vocal cord adduction.
    • Aryepiglottic fold approximation.
  • Swallowing apnea (respiration stops).
  • UES (cricopharyngeus) relaxation & opening.

Flowchart: Key Events in Pharyngeal Phase

Neural Control: Speech & Swallowing - Brain & Nerve Command

• Brain Centers:
  • Speech: Broca's area (motor), Wernicke's area (sensory), Arcuate Fasciculus.
  • Swallowing: Medulla oblongata (NTS - sensory input, NA - motor output).
• Key Cranial Nerves:

  Nerve	Speech Function	Swallowing Function
  V	Jaw movement	Mastication
  VII	Lip movement	Lip seal, hyoid elev.
  IX	Palate, pharynx	Pharyngeal sens/const.
  X	Phonation, palate	Pharynx, larynx, esoph.
  XII	Tongue (articulation)	Tongue (bolus control)

  • (CN XI assists CN X for pharynx/larynx)

⭐ The nucleus ambiguus (medulla) is key for swallowing, innervating pharynx/larynx/upper esophagus via CN IX, X, XI.

High‑Yield Points - ⚡ Biggest Takeaways

• Speech production: Respiration (power), phonation (laryngeal source), resonance (vocal tract filter), articulation (sound shaping).
• Vocal cords: Abducted for breathing, adducted/vibrating for phonation; RLN injury typically causes hoarseness.
• Swallowing phases: Oral (voluntary), pharyngeal (involuntary, rapid, airway protection crucial), esophageal (involuntary peristalsis).
• Key Cranial Nerves for speech & swallowing: V, VII, IX, X, XII.
• Aspiration risk: Highest during pharyngeal phase if laryngeal protection (elevation, closure) fails.
• Velopharyngeal closure: Prevents nasal regurgitation during swallowing and for non-nasal speech.