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Laryngeal Structure & Function; Vocal Fold Vibration

2/8/00

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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

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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.

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Laryngeal Cartilage's

• 3 Unpaired Cartilage's

-Epiglottis

-Thyroid

-Cricoid

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• 3 Paired Cartilage's

-Cuneiform

-Corniculate

-Arytenoid

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Larynx & Trachea

Hyoid Bone

Thyoid Cartilage

Crioid Cartilage

Tracheal Ring

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Laryngeal Cartilages

Cricoid

Vocal Ligament

Thyroid

Superior horn

Inferior horn

ThyroidNotch

Stretched

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Arytenoid Movement

Rocking

AbductedAdducted

Gliding

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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 musclesSuprahyoid & Infrahyoid

• Anatomical position: Suprahyoid- one of the above attachments lies above the larynx.Infrahyoid- one of the attachments lies

below the larynx.

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Extrinsic laryngeal Muscles

Mastoid Tip

Mylohyoid

Hyoid Bone

Sternohyoid

Omohyoid

Sternum

Mandible

Ant.Digastric

Post.Digastric

Stylohyoid

Thyrohyoid

Sternothyroid

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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.

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Intrinsic Muscles:

• Cricothyroid: fan-shaped, 2 divisions, Lengthens & tenses the vocal folds.

Action of Cricothyriod

Pars obliquePars recta

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Intrinsic Muscles

• Thyroarytenoid: muscle making up the true vocal folds, 2 parts: thyrovocalis (bound to the vocal ligament) & thyromuscularis (lateral to arytenoids).

ThyroarytenoidVocal ligament

Thyrovocalis

Thyromuscularis

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Intrinsic Muscles

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

PosteriorCricoarytenoid

Action of Post.Cricoarytenoid

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Intrinsic Muscles

• Lateral Cricoarytenoid: lies along upper surface of cricoid cartilage, adducts vocal processes of arytenoids closing membranous portion of v.f.’s.

Action of Lat.Cricoarytenoid

LateralCricoarytenoid

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Intrinsic Muscles

• Interarytenoids (transverse & oblique): Unpaired, 2 part muscle, adducts the v.f.’s in the cartilaginous portion by pulling arytenoid tips together.

ObliqueInterarytenoids

TransverseInterarytenoids

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The 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

Glottis

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Vocal Fold Vibration

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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

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Surface Wave

Top = Coronal sectionBottom = Motions of upper and lower margins (Superior view)

Posterior

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Vocal Cord Vibration

22• Note how the vocal folds open from bottom to

top & back to front.

Spread of glottal opening

Vertical Phase difference

Anterior

Superior

Inferior

Vertical & Horizontal Movement of Vocal Fold Vibration

Posterior

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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

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UpperMass

LowerMass

Upper Mass

Lower Mass

Two-Mass Model•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

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Regulation of Fundamental Frequency

• Longitudinal tension = regulation of frequency– Laryngeal muscle adjustments (change

length & tension)• f0 = 1/2L (T/) 0.5

–T= Tension of vocal fold mucosal cover,

– = Density of the tissue & L = Length of folds

• F0 is determined primarily by tension of the vocal fold cover and not by length

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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

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Amplitude of Soft & Loud Vocal Fold Vibration

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Other Laryngeal Functions

• Vocal fold opening: inspiration, silent pause, whisper, voiceless sounds

• Medial compression: excessive closure for lifting, childbirth, defecation