Laryngeal Structure & Function; Vocal Fold Vibration 2/8/00

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

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.

Laryngeal Cartilage's 3 Unpaired Cartilage's -Thyroid -Cricoid -Epiglottis -Thyroid -Cricoid

3 Paired Cartilage's -Cuneiform -Corniculate -Arytenoid

Larynx & Trachea Tracheal Ring Hyoid Bone Thyoid Cartilage Crioid Cartilage

Laryngeal Cartilages Thyroid Thyroid Notch Superior horn Cricoid Vocal Ligament Superior horn Stretched Cricoid Inferior horn

Arytenoid Movement Rocking Gliding Adducted Abducted

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.

Extrinsic laryngeal Muscles Mandible Mastoid Tip Mylohyoid Hyoid Bone Sternohyoid Omohyoid Sternum Ant. Digastric Post. Digastric Stylohyoid Thyrohyoid Sternothyroid

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.

Intrinsic Muscles: Pars recta Action of Cricothyriod Pars oblique Pars recta Cricothyroid: fan-shaped, 2 divisions, Lengthens & tenses the vocal folds.

Intrinsic Muscles Vocal ligament Thyroarytenoid Thyrovocalis Thyromuscularis Thyroarytenoid: muscle making up the true vocal folds, 2 parts: thyrovocalis (bound to the vocal ligament) & thyromuscularis (lateral to arytenoids).

Intrinsic Muscles Action of Post. Cricoarytenoid Posterior Posterior Cricoarytenoid: Abducts the vocal folds, actively contracted at the end of phonation & any speech sound not requiring v.f. vibration.

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.

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.

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

Vocal Fold Vibration

Phonation Subglottal pressure develops Folds begin to vibrate 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

Surface Wave Posterior Top = Coronal section Bottom = Motions of upper and lower margins (Superior view)

Vocal Cord Vibration

Vertical & Horizontal Movement of Vocal Fold Vibration Anterior Posterior Spread of glottal opening Superior Inferior Vertical Phase difference Note how the vocal folds open from bottom to 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

Two-Mass Model Upper Mass Lower Mass Upper Mass Lower Mass Two masses connected by a spring Vibratory pattern has horizontal & vertical components Mechanical (elastic) forces Body responsible for lateral motion Cover responsible for surface-wave behavior Upper Mass Lower Mass Upper Mass Lower Mass

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 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

Amplitude of Soft & Loud Vocal Fold Vibration

Other Laryngeal Functions Vocal fold opening: inspiration, silent pause, whisper, voiceless sounds Medial compression: excessive closure for lifting, childbirth, defecation