Physiology of Speech and Swallowing

Physiology of Speech and Swallowing

Physiology of Speech and Swallowing

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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.

Larynx and Vocal Fold Anatomy

⭐ 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.
    ArticulatorRole / Sounds
    LipsBilabials (p, b, m), rounding
    TongueVowels, consonants (t, d, k, g)
    TeethDentals (th), labiodentals (f, v)
    Hard PalatePalatals (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).

Sagittal view of head and neck anatomy for speech/swallowing

⭐ 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.

Phases of Swallowing and Airway Protection

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:
    NerveSpeech FunctionSwallowing Function
    VJaw movementMastication
    VIILip movementLip seal, hyoid elev.
    IXPalate, pharynxPharyngeal sens/const.
    XPhonation, palatePharynx, larynx, esoph.
    XIITongue (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. Cranial Nerves for Speech and Swallowing

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.

Practice Questions: Physiology of Speech and Swallowing

Test your understanding with these related questions

Which of the following changes in voice is not produced as a result of external laryngeal nerve injury post thyroidectomy?

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Flashcards: Physiology of Speech and Swallowing

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In adenoid hypertrophy voice is toneless and loses nasal quality due to nasal obstruction i.e. rhinolalia _____.

TAP TO REVEAL ANSWER

In adenoid hypertrophy voice is toneless and loses nasal quality due to nasal obstruction i.e. rhinolalia _____.

clausa

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