Development of Phonation PDF

Development and aging in phonation JP Louboutin 30/9/2024  PRENATAL DEVELOPMENT OF THE PHONATORY MECHANISM Development of the larynx is intertwined with that of the respiratory mechanism  Formation of neural tube...

Development and aging in phonation JP Louboutin 30/9/2024  PRENATAL DEVELOPMENT OF THE PHONATORY MECHANISM Development of the larynx is intertwined with that of the respiratory mechanism  Formation of neural tube - Neurulation: process whereby neural plate forms neural tube - The neural plate develops a neural groove which then deepens and is bounded on either side by neural folds - Gradually, the neural folds fuse converting the neural groove into a neural tube  Formation of neural tube - Neurulation: process whereby neural plate forms neural tube - The neural plate develops a neural groove which then deepens and is bounded on either side by neural folds - Gradually, the neural folds fuse converting the neural groove into a neural tube  Development of neural tube - In earliest stages, neural tube remains in communication with amniotic cavity through anterior and posterior neuropores Anterior neuropore Neural plate Fusion of neural folds Posterior neuropore - Later, the anterior neuropore closes first, then the posterior neuropore. Neural tube closure is complete within 28 days. Neural tube located beneath the surface ectoderm Closure of neuropores at 25 and 28 days Formation of neural crest - During the invagination of the neural plat form the neural groove, cells forming the la margin of the plate do not become incorpor in the neural tube but instead form a strip o ectodermal cells that lie between the neura tube and the covering ectoderm. This strip o cells is called neural crest - Neural crest will undergo epithelial-to mesenchymal transition as it leaves neuroectoderm by active migration to enter underlying mesoderm - Cells of the neural crest will differentiate into cells of posterior root ganglia, sensory ganglia of cranial nerves, autonomic ganglia, melanocytes, cells of suprarenal medulla, Schwann cells  WEEK 4 Week 4: Neural crest cell migration occurs Migrate from margins of neural plate Will differentiate to form structures of head and neck Become the pharyngeal arch system  THE PHARYNGEAL ARCHES OF PHONATION Hyoid Arch (2nd arch): Part of hyoid bone 3rd Arch: the rest of the hyoid bone 4th & 6th Arches: pharyngeal, recurrent, superior laryngeal nerves of X vagus; Extrinsic and intrinsic laryngeal muscles Thyroid, corniculate, cuneiform, and arytenoid cartilages  TIMELINE OF DEVELOPMENT Early in 4th week the laryngotracheal diverticulum develops from pharyngeal tube, then forms the respiratory bud (later to be lungs) Respiratory tree communicates with pharyngeal tube by means of laryngeal inlet: this will become the aditus to the larynx Splanchnic mesenchyme of 4th & 6th arches will develop into the cartilages Arytenoids develop as a swelling; then glottis, laryngeal ventricles, vocal folds, epiglottis, ventricular folds End of week 4: Respiratory system arises from the laryngotracheal pouch of the 4 th pharyngeal arch Endoderm of 4th arch forms glands of larynx, trachea and bronchi, and pulmonary epithelium WEEKS 4 - 8  BETWEEN DAYS 28 AND 32 Week 4: Trachea separates from esophagus as bronchial buds emerge Week 5: tracheoesophageal tube develops from the diverticulum, and there will be larynx, trachea, bronchi, lungs  BIRTH AND GROWTH Vocal fold length: Vocal folds are about 4 mm long at birth Will be 12-15 mm long in teens Changes happen in puberty Sexual dimorphism at puberty Adult males: 17.5 to 25 mm Adult females: 12.5 to 17.5 mm  Histology of larynx: 5 layers 1. Cover - 3 elements: epithelium (mucosa), basal lamina or basement membrane zone (BMZ), and superficial layer of the lamina propria + Epithelium - Free edge of vibratory portion of vocal fold, anterior glottis, is covered with stratified squamous non-keratinized epithelium. This epithelium is five to twenty-five cells thick - On surfaces of epithelial cells are microridges and microvilli. Lubrication of the vocal folds through adequate hydration is essential for normal phonation to avoid excessive abrasion, and the microridges and microvilli help to spread and retain a mucous coat on the epithelium - Epithelium described as a thin shell, the purpose of which is to maintain the shape of the + Basal lamina or basement membrane zone (BMZ) - Two zones, lamina lucida and lamina densa. + Lamina lucida: low density clear zone medial to the epithelial basal cells + Lamina densa: greater density of filaments and adjacent to lamina propria. BMZ mainly provides physical support to the epithelium through anchoring fibers and is essential for repair of epithelium + Superficial layer of the lamina propria - Consists of loose fibrous components and extracellular matrices that can be compared to soft gelatin. Also known as Reinke’s space but it is virtual space - Structure that vibrates a great deal during phonation, and the viscoelasticity needed to support this vibratory function depends mostly on extracellular matrices - Primary extracellular matrices of the vocal fold cover contain reticular, collagenous and elastic fibers, as well as glycoproteins and glycosaminoglycans - Fibers serve as scaffolds for structural maintenance, providing tensile  2. Transition + Intermediate and deep layers of the lamina propria - Intermediate layer of the lamina propria primarily made up of elastic fibers while the deep layer of the lamina propria primarily made up of collagenous fibers - These fibers run roughly parallel to the vocal fold edge and these two layers of the lamina propria comprise the vocal ligament - Transition layer primarily structural, giving the vocal fold support as well as providing adhesion between the mucosa, or cover, and the body, the thyroarytenoid muscle  3. Body + Thyroarytenoid muscle - Muscle variously described as being divided intovocalis muscles or thyrovocalis and the thyromuscularis, depending on the source  VOCAL FOLD TISSUE CHANGES 5 layers of vocal folds Superficial lamina propria (SLP) Intermediate lamina propria (ILP) Deep lamina propria (DLP)  FROM BIRTH THROUGH PUBERTY At 2 months, SLP starts to differentiate. Only one in young child By 7-10 years all three layers can be found By 10-16 years layers are adult- like Lamina propria has important implications for vibratory qualities, and this differentiates the voices of children versus adults  ELASTIN AND COLLAGEN CHANGES These are part of the extracellular matrix, which supports the cells of the tissues themselves Elastin: provides elasticity Collagen: provides structure/support that reduces injury What changes from infancy to adulthood?  ELASTIN AND COLLAGEN DURING DEVELOPMENT Adults: SLP has no collagen or elastin ILP has elastin but little collagen DLP has mostly collagen, with little elastin Infants: Have about 50% of adult elastin and collagen Develops and distributes into the layers as infant develops Older adults: Lose elastin, but keep or increase collagen  CARTILAGE CHANGES DURING DEVELOPMENT At birth: Larynx is about 33% of adult size Cartilage continues to grow into adulthood Cartilage becomes stiffer with age At puberty: Thyroid and cartilage grow Male thyroid cartilage is twice the weight of female Prominent thyroid angle (“Adam’s apple”) Cartilage growth is complete at 20  HYOID AND LARYNGEAL DESCENT DURING DEVELOPMENT Hyoid: Ossification of hyoid occurs shortly after birth At birth, hyoid is at level of C2/C3 vertebrae, larynx is at C3/C4 By 2 years, larynx and hyoid are at adult locations (C3/C6 and C4) Torso is also growing, so vocal tract is lengthening Increases resonatory volume, including subglottal space  FUNDAMENTAL FREQUENCY CHANGE DURING DEVELOPMENT Neonate has highest f0, and it drops steadily towards puberty Sexual dimorphism strongly present at 30 28 27.52 puberty as vocal fold 25 24.48 22.96 Maximum duration in seconds mass and length 20 22 20 20 22 22 21 21 21.18 increases 17 18 15 15 14 As respiration develops, 10 10 10 ability to sustain 8 5 phonation increases to peak in 20s 0 3 5 7 9 11 13 15 17 0 9 -7 -8 61 81 Age in Years  FUNDAMENTAL FREQUENCY CHANGES WITH AGING Adult male f0 is around 130 Hz at 20 years, then starts increasing around 140 Hz at 80 years 30 28 27.52 25 Female f0 is 190 Hz at 20, and it 24.48 Maximum duration in seconds 22.96 22 2222 2121 21.18 20 2020 holds relatively steady into older age 15 15 17 18 14 10 1010 8 5 0 Age in Years AGING EFFECTS ON STRUCTURE AND FUNCTION OF THE PHONATORY MECHANISM Change as we age co-occur with respiratory changes Remember that respiration and phonation go hand-in-hand: The weaker the respiration, the weaker the phonatory product Respiration begins decline in 20s, and so does the vocal mechanism Presbyphonia: phonatory characteristics of geriatric vocal mechanism Prebylarynx: the aging laryngeal structures  VOCAL EFFECT OF PRESBYPHONIA Hoarseness Low vocal intensity Increased breathiness Vocal fatigue Reduced vocal harmonics  SUPPORTIVE TISSUE CHANGES Remember the lamina propria: SLP, ILP, DLP Both collagen and elastin, giving strength and elasticity Elastin decreases with age and collagen increases This means that the vocal folds get stiffer and less elastic Produces increased vocal fatigue and hoarseness, as well as reduced f0 range Vocal ligament becomes more thins and frail  MUSCLE CHANGES WITH AGING Sarcopenia: muscle atrophy Lose muscle fibers, and the existing fibers become thinner and smaller in diameter Thyroarytenoid is very vulnerable, starting at around 60 years old Weak thyrovocalis results in breathy phonation and inefficient use of already weakened respiration Loss of elastin may result in bowing of vocal folds Larynx descends farther into pharynx because of weak supraglottal muscles CARTILAGE AND NERVE CHANGES WITH AGING Cartilage: Laryngeal cartilage ossifies with age (except epiglottis) Ossification starts around 18 years of age and is complete around 70 years Nerves: Laryngeal nerves are very vulnerable to aging Progressive deterioration causes the action potential declines after 60 years Results in inadequate adduction, f0 change, breathiness, increased vocal jitter Also has reduced sensitivity, so more vulnerable to foreign body entry into larynx  OTHER ACOUSTIC PARAMETERS AND AGING Vocal jitter: as we age it gets larger, because of increased variability of phonation Vocal intensity: Phonation gets weaker as we age Vocal range: it gets smaller as we age Harmonic-to-Noise ratio: This increases as we age THANK YOU!