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

(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

Clinical Application - Talking w/ your patients:

•  You are working with an adult patient who has

  a voice disorder. They know nothing about

  vocal physiology. Explain vocal fold vibration

  to your patient. Make sure to define clearly

  any technical words, and to keep explanations

  as simple but accurate as you can.