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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
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Laryngeal Cartilages
Thyroid
Thyroid
Notch
Vocal Ligament
Superior horn
Cricoid
Inferior horn
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Arytenoid Movement
Rocking
Gliding
Adducted
Abducted
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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 muscles
Suprahyoid & 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
Mandible
Ant.
Digastric
Post.
Digastric
Stylohyoid
Mastoid Tip
Mylohyoid
Hyoid Bone
Thyrohyoid
Sternohyoid
Omohyoid
Sternothyroid
Sternum
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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:
Action of Cricothyriod
Pars oblique
Pars recta
• Cricothyroid: fan-shaped, 2 divisions,
Lengthens & tenses the vocal folds.
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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).
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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.
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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.
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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
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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
Posterior
Top = Coronal section
Bottom = Motions of upper and lower margins (Superior view)
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Vocal Cord Vibration
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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
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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
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•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
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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
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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
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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
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