Phonatory system

The Larynx

Core Structure: The Larynx

• Primary role: Voice production via vocal fold vibration

• Also involved in airway protection and valsalva-type functions

 

🧬 Key Anatomical Features

Structure	Function
Vocal folds (true vocal cords)	Vibrate to produce sound; modulate pitch and loudness
Glottis	Opening between vocal folds; controls air passage and phonation onset
Cartilages (thyroid, cricoid, arytenoid)	Provide structure and mobility for phonatory control
Intrinsic laryngeal muscles	Control tension, length, and position of the vocal folds (e.g. cricothyroid, thyroarytenoid)

 

 

🗣 Functional Aspects of Phonation

• Requires subglottic air pressure (discussed previously)

• Vocal fold approximation: Vocal folds must adduct properly for vibration to occur

• Tension modulation: Alters pitch and quality

 

📉 Dysfunctions of the Phonatory System

Dysfunction	Possible Causes	Clinical Signs
Incomplete glottic closure	Weakness/paralysis of adductors	Breathy voice
Hyperadduction	Excess tension (e.g. spastic dysarthria)	Strained or harsh voice
Reduced tension	LMN lesion (e.g. recurrent laryngeal nerve palsy)	Monotone or hoarseness

 

 

🧩 Links to Sensorimotor Disorders (e.g. Parkinson’s)

• Reduced vocal loudness (hypophonia) due to:

  • Poor respiratory support

  • Reduced vocal fold closure

  • Impaired coordination of laryngeal muscles

• Monotonicity and limited pitch variation

• Can be assessed using tools like acoustic analysis, laryngoscopy, or perceptual scales (e.g. GRBAS)

Functional Requirements of the Phonatory System

Structural Requirement: True Vocal Folds

• Contain the vocal ligaments

• Extend from the thyroid cartilage (anteriorly) to the arytenoid cartilages (posteriorly)

 

📌 Functional Requirement 1: Vocal Fold Vibration

• Essential for phonation (voice production)

• Vibration occurs when air passes through adducted vocal folds under sufficient subglottic pressure

 

📌 Functional Requirement 2: Adduction of the Vocal Folds

To produce voice, the vocal folds must be brought together (adducted). This requires:

🔹 Key Muscles Involved:

Muscle	Function
Lateral cricoarytenoid	Rotates arytenoid cartilages medially to adduct the vocal folds
Inter-arytenoid muscles (transverse & oblique)	Pull arytenoid cartilages together, closing the posterior glottis (cartilaginous portion)

 

 

🔁 Comparison: Speech vs. Whisper

Parameter	Speech	Whisper
Vocal Fold Position	Adducted (vibrating)	Partially abducted (posterior glottis remains open)
Sound Production	Phonation with vocal fold vibration	No vocal fold vibration (turbulent airflow)
Muscles Active	Lateral cricoarytenoid + inter-arytenoids	Reduced or altered activity to keep posterior gap open

 

 

⚠ Clinical Relevance

• Hypoadduction (e.g. vocal fold paresis): Breathiness, weak voice

• Hyperadduction (e.g. spasticity): Strained, harsh voice

• Poor coordination: Irregular pitch, effortful phonation

Vocal Fold Adduction & Tension: Functional Insights

(Key Muscles and Clinical Relevance for Sensorimotor Speech Disorders)

 

🎯 Why Tension Matters in Vocal Fold Adduction

• Adduction alone isn't enough — the tension within the vocal folds is crucial for:

  • Accurate pitch modulation

  • Efficient vibration

  • Clear voice quality

 

🔍 Two Key Components of Tension

1. Ligamentous Part (vocal ligaments)

2. Cartilaginous Part (posterior portion of folds)

 

💪 Muscles Controlling Tension

🔹 1. Cricothyroid (CT) Muscle

• External muscle

• Action: Tilts the thyroid cartilage forward relative to the cricoid

• Function: Increases vocal fold tension (raises pitch)

🔹 2. Thyroarytenoid (TA) Muscle

• Internal to the vocal folds

• Action: Pulls arytenoid cartilages toward the thyroid

• Function: Relaxes the vocal folds (lowers pitch or reduces tension)

🔹 3. Vocalis (or Thyrovocalis) Muscle

• Part of the thyroarytenoid

• Function: Fine-tunes localised tension within vocal folds — allows subtle pitch adjustments and dynamic control

 

🔁 Functional Summary: Tension + Adduction

Muscle	Role in Tension	Role in Adduction
Cricothyroid	Increases tension	No direct role
Thyroarytenoid	Decreases tension	Assists with medial compression
Vocalis	Fine control of tension	Assists with shape & vibration quality

 

 

🧪 Clinical Relevance for Assessment

• Observe pitch control, voice fatigue, strain, or breathiness

• Weakness or incoordination may point to:

  • Flaccid dysarthria (e.g. vocal fold paresis → poor adduction)

  • Spastic dysarthria (hypertonicity → excessive tension)

  • Hypokinetic dysarthria (e.g. in Parkinson’s → reduced dynamic range, monotone)

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