Normal Phonatory Mechanisms and Laryngeal Muscles

Normal Phonatory Mechanisms

• Normal phonation: vocal folds (VF) approximate along the entire anterior-posterior dimension, termed phonatory expiration.
• Slight posterior glottal chink: more common in females, a subtle posterior opening in the folds, a normal variation, not a pathology. (subtle breathiness).
• Non-phonatory expiration: VF abducted but not at extreme positions, no voice production, just exhaling.
• Forced inspiration: VF widely abducted, deep inhalation.
• Whisper phonation: anterior 2/3 of VF approximate, posterior chink. Acoustic perception of turbulence (whisper sound), not good for vocal mechanism, aperiodic, significant posterior glottal opening.

Intrinsic Laryngeal Muscles

• Six intrinsic muscles: responsible for altering vocal fold position and status.
• Posterior cricoarytenoid (2): only abductor (opens glottis), rocks arytenoids dorsally, innervated by recurrent laryngeal nerve.
• Lateral cricoarytenoids (2): adductors, pull muscular and vocal processes medially for vocal fold approximation. Medial compression for phonation posture, innervated by inferior laryngeal nerve (vagus nerve).
• Cricothyroid (2): adductors, stretch and tense VF, increasing pitch (innervated by superior laryngeal nerve).
• Transverse arytenoid (1): adductor, approximates arytenoid cartilages, helps with adduction, innervated by recurrent laryngeal nerve.
• Oblique arytenoids (2): adductors, pulls arytenoids medially, innervated by recurrent laryngeal nerve.
• Thyroarytenoids (2): bulk of VF muscles, lower pitch, antagonistic to cricothyroid. Lateral portion = thyromuscularis, medial portion = vocalis, differential tensing for phonatory control

Acoustic Properties of Sound

• Three perceptual characteristics: pitch, loudness/intensity, quality/timbre.
• Pitch (frequency): number of vibrations per second (Hz); related to size, material, shape, and motion of sound source.
• Octave: interval with frequency ratio of 2:1.
• Intensity (loudness): energy, measured in decibels (dB); louder sounds have more energy.
• Quality/timbre (harmonic constitution/waveform): combination of sounds, fundamental frequency (F0) and harmonics.
• Periodic sounds: regular, repeated vibrations, pleasant, mostly vowels.
• Aperiodic sounds: irregular, not repeated, harsh, mostly consonants.

Voice Production Theories

• Puff theory: simplistic, inadequate, air puffs initiating vibration, doesn't address tension, adduction/abduction.
• Neurochronaxix theory: inaccurate, each vibratory cycle initiated by nerve impulse; doesn't account for subglottal pressure or anatomical differences.
• Myoelastic aerodynamic theory: considers air pressure, muscle involvement, and elastic properties of vocal folds, correct model for phonation.

Factors Affecting Pitch, Loudness and Voice Quality

• VF length/thickness & tension affect pitch. Longer/thinner/tenser folds vibrate faster (higher pitch), short/thicker/laxer vibrate slower (lower pitch).
• Higher pitches require increased subglottal pressure and VF tension. Lower pitches require relaxation of cricothyroids + contraction of thyroarytenoids.
• Laryngeal function relates to protection and voice production (secondary).

Vocal Aging

• Older adults (69+): experience muscular atrophy, mucosal thinning/dehydration, ligament loss of elasticity, cartilage calcification, vocal fold bowing, and edema.
• Sarcopenia: natural muscle loss with aging.
• Presbyphonia: natural vocal changes associated with aging. Male F0 tends to rise, female F0 falls.

Vocal Quality Assessment

• CAPE-V: clinical research tool for standardized auditory-perceptual voice assessment. Assesses severity, roughness, breathiness, strain, pitch, loudness.
• Voice Handicap Index (VHI): self-report instrument measuring functional, physical, and emotional impact of voice disorders on daily life.
• Jitter: short-term variability in frequency.
• Shimmer: short-term variability in amplitude.

Classification of Voice Disorders

• Functional Voice Disorders: result from abnormal use/misuse. Includes muscle tension dysphonia (MTD), psychogenic disorders (emotional/psychological origin), paradoxical vocal fold movement (PVFM).
• Organic Voice Disorders: result from physiological abnormality of structure/function in vocal mechanism (l.e. cancer, infections, endocrine disorders).
• Vocal nodule/polyps, Reinke's edema, traumatic laryngitis, contact ulcers/granulomas, vocal fold thickening, falsetto, phonation breaks, pitch breaks, diplophonia, aphonia, dysphonia, functional dysphonia, conversion aphonia, mutational falsetto, hypernasality, hyponasality, cul-de-sac resonance

Assessment Tools

• S/Z ratio: screening measure of expiratory control and phonatory control (Normal = 1:1 or less)

Explore the normal phonatory mechanics and the role of intrinsic laryngeal muscles in voice production. Understand concepts like phonatory expiration, whisper phonation, and the function of key muscles such as the posterior cricoarytenoid. This quiz covers essential aspects of vocal fold behavior and muscle action crucial for effective phonation.