Anatomy & Physiology of Larynx

What is a voice disorder?

• exists when a person’s quality, pitch, & loudness differ from those of similar age, gender, cultural background, & geographic location

• exists when either the structure, the function, or both of the laryngeal mechanism no longer meet the voicing requirements established for the mechanism by the speaker

What are the 3 subsystems of voice?

• Respiration

• Phonation

• Resonance

The Laryngeal Valve:

• Cartilage

• Muscles

• Connective Tissues

• Mucosa

(Laryngeal Valve) What are the 3 basic functions of the laryngeal valve?

• Airway Preservation for Ventilation

• Airway Protection (especially during swallowing)

• Phonation (for communication & singing)

(Laryngeal Valve) Three Levels of Folds:

• Aryepiglottic Folds

• Ventricular Folds

• True Vocal Folds

Vocal Folds:

• True vocal folds

• Space between = glottis

• 20 mm x 8 mm (adult M)

• Subglottal (below) & supraglottal (above)

(Respiration for Phonation) What does phonation rely on?

• pulmonary respiratory power

  • Abdominal & Thoracic Musculature

  • Lungs within Ribcage

  • Diaphragm (primary muscles of quiet inspiration)

  • Pleural Lining (double-walled)

(Muscles of Respiration) What are the muscles of inspiration?

• Diaphragm

• External Intercostals

• Sternocleidomastoids

• Scalenes

• Pectoralis (major & minor)

(Muscles of Respiration) What do the muscles of expiration work in concert with?

• passive forces of torque, tissue elasticity, & gravity

(Muscles of Respiration) During speech, the expiratory muscles assist passive forces to:

• Compress the abdominal viscera

• Force diaphragm upward & depress lower ribs

• Decrease thoracic cavity size – sustain pulmonary pressure

(Muscles of Respiration) What are the muscles of expiration?

• Internal Intercostals

• Rectus Abdominis

• Transverse Abdominis

• Internal Obliques

• External Obliques

Structural Support for the Larynx:

• Hyoid Bone

• Laryngeal Cartilages (n = 9)

  • Epiglottis

  • Thyroid

  • Cricoid

• 3 paired smaller cartilages

  • Arytenoids

  • Corniculates

  • Cuneiforms

(Cartilages & Hyoid Bone) What are the cartilages connected by?

• all connected by ligaments & lined w/ mucous membrane

(Laryngeal Muscles) Extrinsic Muscles:

• One attachment within the larynx & the other attachment outside of the larynx

• Influence overall laryngeal height or position within the neck

• Alter shape & filtering characteristics of the supraglottic vocal tract

• Modifies vocal pitch, loudness, & quality

(Extrinsic Laryngeal Muscles) What are the suprahyoid muscles?

• Function: Raise the larynx

  • Digastrics (anterior & posterior bellies)

  • Stylohyoid

  • Mylohyoid

  • Geniohyoid

• “Don’t Stop Munching Guacamole”

(Extrinsic Laryngeal Muscles) What are the infrahyoid muscles?

• Function: Lower the hyoid & larynx

  • Thyrohyoid

  • Sternothyroid

  • Sternohyoid

  • Omohyoid

• Tina Sees SpongeBob Often

(Intrinsic Laryngeal Muscles) How many intrinsic laryngeal muscles are there?

• 5

(Intrinsic Laryngeal Muscles) What is the function of the intrinsic laryngeal muscles?

• Affect the position, length, & tension of the vocal folds

  • change position of the cartilage framework that houses the vocal folds

  • alter the length, tension, & shape of the vocal fold edge, including thickness

  • change the shape of the glottal opening between the vocal folds

(Intrinsic Laryngeal Muscles) Cricothyroid (CT):

• Tensor

(Intrinsic Laryngeal Muscles) Thyroarytenoid (TA):

• ADDUCTOR

• sometimes called the vocalis

(Intrinsic Laryngeal Muscles) Lateral Cricoarytenoid (LCA):

• ADDUCTOR

(Intrinsic Laryngeal Muscles) Interarytenoid (IA):

• ADDUCTOR

• Transverse (Horizontal)

• Oblique (Crossed)

(Intrinsic Laryngeal Muscles) Posterior Cricoarytenoid (PCA):

• ABDUCTOR

• pull the arytenoid cartilages inferiorly

• moves the vocal process tips laterally & abducts VFs

Vocal Fold Microstructure:

• Membranous portions of the VFs oscillate (vibrate) to create sound

• The integrity of the vibratory pattern for phonation requires a pliable, elastic structure

• Adult VFs contain 5 discrete histological layers that vary in composition & mechanical properties

  • Provide variable amounts of flexibility & stability

Layered Structure of the Vocal Fold:

• Five layers → from most superficial to deep

  • Epithelium

  • Lamina Propria (LP)

    • Superficial (i.e., SLLP)

    • Intermediate (i.e., ILLP)

    • Deep (i.e., DLLP)

  • Vocalis Muscle

What is there an increase in as the layers progress from superficial to deep?

• density & stiffness of tissue

• this stiffness gradient is critical for sustained vocal fold oscillation!

Epithelium:

• Outermost, mucosal layer, thin pliable capsule

• Thin layer of slippery mucous lubrication needed for VFs to oscillate best

(Epithelium) What covers epithelium?

• Mucociliary blanket

  • Mucionous layer (outermost viscous protective layer)

  • Serous layer (watery layer w/ cilia)

(Epithelium) What environmental influences is epithelium exposed to?

• Humidity

• Dehydration

• Pollution

• Reflux

(Epithelium) What is the transition zone of the epithelium?

• Basement Membrane Zone (BMZ)

Lamina Propria (LP):

• 3 layered structure

  • Superficial layer (SLLP)

  • Intermediate (middle) layer (ILLP)

  • Deep layer (DLLP)

(Lamina Propria) What is each layer of the LP composed of?

• distinct concentrations of fibrous proteins (connective tissue)

  • Elastic (allows tissue to deform/stretch)

    • most concentrated in SLLP & ILLP

  • Collagen (less stretch, but tolerate stress & provides tensile strength)

    • Most concentrated in ILLP & especially in DLLP

  • As progress from superficial to deep layers of the LP there is increasing density/stiffness

  • LP vibrates passively in response to aerodynamic forces

(Lamina Propria) Superficial layer (SLLP)/ Reinke’s Space:

• Loose & flexible

• Soft, slippery, gelatin-like substance

• Vibrates significantly during phonation

(Lamina Propria) Intermediate (middle) layer (ILLP):

• Mostly elastic fibers (some collagen)

• Also vibrates during phonation

(Lamina Propria) Deep layer (DLLP):

• Mostly collagen fibers (fewer elastin fibers) - most dense layer of LP

• Interspersed w/ muscle fibers to join LP to underlying vocalis muscle

• *Note: The combined intermediate & deep layers of the lamina propria is also known as the “Vocal Ligament”

Vocalis Muscle:

• 5th histological layer (most dense)

• Forms the “body” of the VF & provides:

  • Tone

  • Stability

  • Mass

• _____ still oscillates during VF vibration (but not as much as cover & transition layers of VF)

Layered Structure Reconsidered:

• 5 vs. 3 vs. 2 layers??

• 5 layers regrouped into 3 vibratory divisions:

  • Cover = Epithelium & Superficial Layer of LP

  • Transition = Intermediate & Deep Layers of LP

  • Body = Vocalis Muscle

• 5 layers regrouped into 2 vibratory divisions:

  • Cover = Epithelium, SLLP, ILLP (flexible)

  • Body = DLLP & Vocalis m. (> greater density/stiffness)

Neurologic Supply:

• Central Nervous System Control

• Peripheral Innervation

• Laryngeal Reflexes

(Neurologic Supply) Central Nervous System Control:

• Sensory receptors (afferent pathways)

• Motor commands (efferent pathways)

(Neurologic Supply) Peripheral Innervation:

• CN X - Vagus (“wandering”)

• Superior Laryngeal Nerve (SLN)

• Recurrent Laryngeal Nerve (RLN)

(Neurologic Supply) Superior Laryngeal Nerve (SLN):

• Internal (sensory) larynx above VFs

• External (motor) principally the Cricothyroid (CT) muscle

(Neurologic Supply) Recurrent Laryngeal Nerve (RLN):

• The course of the left & right RLN is different

• Motor innervation to all intrinsic (adductor & abductor) laryngeal muscles except the CT

• Sensory (below the VFs)

Developmental Changes:

• Laryngeal Growth & Development

  • Newborns

  • Adult Females

  • Adult Males

• Geriatric VFS

(Physiology of Phonation) What are the theories of vibration?

• Van den Berg’s Aerodynamic-Myoelastic Theory

• Hirano’s Body-Cover Theory

• Titze’s Self-Oscillation Theory

(Physiology of Phonation) Van den Berg’s Aerodynamic-Myoelastic Theory:

• VF Oscillation is a function of 2 contributions:

  • covarying pressure & flow

  • mechanical properties of tissue deformation & collision

(Physiology of Phonation) Hirano’s Body-Cover Theory:

• Important role of the loose, passive (non-muscular) superficial layers (i.e., “Cover” = epithelium, SLLP, ILLP) to VF vibration as compared to the dense, stiff “Body” (i.e., DLLP & Vocalis m.)

• Stiffness gradient of layered structure of VFs (loose pliable Cover vs. dense Body)

(Physiology of Phonation) Titze’s Self-Oscillation Theory:

• Flow-induced self-oscillating system, sustained across time by forces of pressure & flow

• Convergent & Divergent Shaping of VFs in a back & forth motion creates an alternating exchange of airflow & pressure peaks

Bernoulli Principle:

• Brings the folds back together!!!

• Defined as:

  • air passing through a narrow channel (glottis) increases in velocity, decreases in pressure

• VFs are “sucked” back together (negative pressure) bc air flowing thru glottis is a constriction

  • VFs go toward area of lower pressure

More Bernoulli:

• VFs close

• VFs are adducted to “just the right” amount

• Subglottal air pressure develops

• Air pressure pushes them apart

• Air flows between

• Air flow causes VF to come together because of own elasticity (arytenoids are still adducted) & bc of Bernoulli Effect

• Air pressure MUST be higher BELOW VFs than above in order for vibration to happen

Fundamental Frequency Control:

• F0 = rate of VF vibration (cycles per second or Hertz (Hz)

• Acoustic-perceptual correlate of pitch

• Factors that influence F0

  • VF length

  • Longitudinal tension

  • Vibratory amplitude

  • Subglottal pressure

Intensity Control:

• Sound pressure level of acoustic output

• Perceptual correlate is loudness

• Factors that influence intensity:

  • Subglottal pressure

  • VF vibratory phase closure

  • Transglottal flow

  • Supraglottic vocal tract tuning

Phonation Modes (Registers):

• Falsetto (loft)

• Modal (chest)

• Glottal fry (pulse)

(Phonation Modes/Registers) Falsetto (loft):

• high-pitched

• strong cricothyroid contraction w/ slightly abducted VFs & vibration only @ the medial edges

(Phonation Modes/Registers) Modal (chest):

• mid-frequency

• thyroarytenoid contracted w/ large vibratory amplitude & complete glottic closure

(Phonation Modes/Registers) Glottal fry (pulse):

• lowest end of frequency range

• pulsed & irregular VF vibration w/ a prolonged closed phase & low subglottal pressure