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Laryngeal Structure & Function; Vocal Fold Vibration 2/8/00 1 Vocal Folds • 5 layers of tissue (deep= muscle) • Glottis= space between the vocal folds • Subglottal= area below the vocal folds • Located at the end of the airstream at superior end of traches 2 Structural Support of the Larynx • Larynx is suspended in the neck by a single bone, the hyoid bone. • There are 6 laryngeal cartilage's: – 3 paired – 3 unpaired – provide structural support for the larynx. 3 Laryngeal Cartilage's • 3 Unpaired Cartilage's -Epiglottis -Thyroid -Cricoid 4 • 3 Paired Cartilage's -Cuneiform -Corniculate -Arytenoid 5 Larynx & Trachea Hyoid Bone Thyoid Cartilage Crioid Cartilage 6 Laryngeal Cartilages Thyroid Thyroid Notch Vocal Ligament Superior horn Cricoid Inferior horn 7 Arytenoid Movement Rocking Gliding Adducted Abducted 8 Extrinsic Laryngeal Muscles • Three Main Purposes: 1) Fixation (primary role) 2) Elevation (move larynx up) 3) Depression (move larynx down) • Two major groups of extrinsic muscles Suprahyoid & Infrahyoid • Anatomical position: Suprahyoid- one of the above attachments lies above the larynx. Infrahyoid- one of the attachments lies below the larynx. 9 Extrinsic laryngeal Muscles Mandible Ant. Digastric Post. Digastric Stylohyoid Mastoid Tip Mylohyoid Hyoid Bone Thyrohyoid Sternohyoid Omohyoid Sternothyroid Sternum 10 Intrinsic Laryngeal Muscles • Functions: 1) Abduction of the vocal folds for respiration, 2) Fine discrete movements during voice production & closure of the vocal folds and, 3) Protection of the trachea. 11 Intrinsic Muscles: Action of Cricothyriod Pars oblique Pars recta • Cricothyroid: fan-shaped, 2 divisions, Lengthens & tenses the vocal folds. 12 Intrinsic Muscles Thyroarytenoid Vocal ligament Thyrovocalis Thyromuscularis • Thyroarytenoid: muscle making up the true vocal folds, 2 parts: thyrovocalis (bound to the vocal ligament) & thyromuscularis (lateral to arytenoids). 13 Intrinsic Muscles Action of Post. Cricoarytenoid Posterior Cricoarytenoid • Posterior Cricoarytenoid: Abducts the vocal folds, actively contracted at the end of phonation & any speech sound not requiring v.f. vibration. 14 Intrinsic Muscles Action of Lat. Cricoarytenoid Lateral Cricoarytenoid • Lateral Cricoarytenoid: lies along upper surface of cricoid cartilage, adducts vocal processes of arytenoids closing membranous portion of v.f.’s. 15 Intrinsic Muscles Transverse Interarytenoids Oblique Interarytenoids • Interarytenoids (transverse & oblique): Unpaired, 2 part muscle, adducts the v.f.’s in the cartilaginous portion by pulling arytenoid tips together. 16 The Glottis Glottis • • • • The glottis is an open space between the vocal folds. Size is dependent on what position the v.f.’s are in. Not a muscle or cartilage. Abduction- open v.f.’s; Adduction- closed v.f.’s 17 Vocal Fold Vibration 18 Phonation • Subglottal pressure develops – Phonatory threshold is reached • 3 cm H20 (.3 kPa) - 6 cm H20 (.6 kPa) • Folds begin to vibrate – Lower subglottal pressure keeps vibration going • Subglottal air pressure pushes the vocal folds laterally & superiorly to initiate vibration • Continuing cycles are sustained by the recoil forces of V.F’s & aerodynamic forces 19 Surface Wave Posterior Top = Coronal section Bottom = Motions of upper and lower margins (Superior view) 20 Vocal Cord Vibration 21 Vertical & Horizontal Movement of Vocal Fold Vibration Anterior Posterior Superior Spread of glottal opening Inferior Vertical Phase difference • Note how the vocal folds open from bottom to 22 top & back to front. Cover Body Theory of Phonation • Vocal adjustments are regulated by changing mechanical properties of the layers of tissue in the vocal folds –Two primary Layers: • Cover (surface of folds) • Body (deeper in the fold) –Layers change in stiffens by different muscle activity 23 •Two masses connected by a spring •Vibratory pattern has Two-Mass Model Upper Mass horizontal & vertical components •Mechanical (elastic) forces •Body responsible for lateral motion •Cover responsible for Lower Mass Upper Mass Lower Mass surface-wave behavior 24 Regulation of Fundamental Frequency • Longitudinal tension = regulation of frequency – Laryngeal muscle adjustments (change length & tension) • f0 = 1/2L (T/r) 0.5 –T= Tension of vocal fold mucosal cover, – r = Density of the tissue & L = Length of folds • F0 is determined primarily by tension of the 25 vocal fold cover and not by length Regulation of Intensity of Phonation • What determines vocal intensity? – Subglottal pressure • Pressure increases & airflow increases through the glottis – Threshold (3-6 kPa= 45-65 dB SPL) – Conversation (below 10 cm H20) – Loud conversation (up to 50 cm H20) • Intensity increases: – Amplitude increases – Longer closed phase of vocal vibration 26 Amplitude of Soft & Loud Vocal Fold Vibration 27 Other Laryngeal Functions • Vocal fold opening: inspiration, silent pause, whisper, voiceless sounds • Medial compression: excessive closure for lifting, childbirth, defecation 28