Speech Pathology Unit 2

Functions of the larynx

• Valve: protective device for lower respiratory tract

  • Prevents air from escaping the lungs (crucial for weight bearing, childbirth, micturition, emesis, defecation - Valsalva)

  • Prevents foreign substances from entering larynx/LRT

  • Aids in forcefully expelling foreign substances that threaten to enter the LRT

  • Aid in swallow

• Anterior and superior movement for 

• Phonation for speech

  • VFs can be modified: stretched, shortened, opened, closed 

Location of the larynx

• Anterior portion of the neck

• Roughly aligned with the C3-C6

  • Individual variation 

  • Can move about 7 cm with extreme flexion and extension of the neck

• Forms the lower part of the anterior pharyngeal wall

• Inferior to thyroid bon

• Superior boundary of trachea 

Spaces/Covaries of the larynx

• Supraglottal

  • Aditus laryngitis

  • Vestibule

  • Vestibular/ventricular folds

  • False Glottis

  • Ventricle

  • True vocal folds

  • Glottis: space between vocal folds 

• Pyriform sinus

• Vallecula

• Subglottal: Atrium- true VFs to inferior margin of cricoid cartilage 

Epithelium

Cover layer of vocal folds

Superficial layer of the lamina propria

Second layer of the vocal folds

Intermediate layer of the lamina propria

Third layer of the vocal folds

Deep layer of the lamina propria

Forth layer of the vocal folds

Vocalis Muscle

Fifth layer of the vocal folds, body

False vocal folds

• Ventricular/vestibular folds: two thick folds of mucous membrane each enclosing a narrow band of fibrous tissue

• Thyroid: arytenoid attachment

Hyoid Bone

• Highly mobile

• Unattached, U-shaped

• Superior attachment for some int. Laryngeal muscles

• Suspends larynx

• Greater and lesser cornua

Thyroid Cartilage Hyaline

• Largest, most prominent “laryngeal prominence”

• Superior thyroid horns attach to greater cornua of thyroid

• Inferior thyroid horns articulate with cricoid cartilage

• Oblique line

• Thyroid notch

Cricoid Cartilage Hyline

• Second largest cartilage

• Circles larynx, 

  • inferior to larynx

  • Superior to trachea

• Two parts: posterior quadrate lamina and anterior arch

• Articulates with horns 

Epiglottis Cartilage elastic

• Concave/convex shape

• Covers entrance to larynx during swallowing

• Cavity between epiglottis on L/R of medial fold and root of tongue called valleculae

• Thyroepiglottic and hyoepiglottic ligaments 

Two arytenoid hyaline

• Pyramid shaped

• Vocal process: pointed projection at anterior angle near base

• Located in and articulate posterior cricoid cartilage

• Upwards and outward swinging movements to close/open folds 

Two corniculate elastic

• Horn-like shape

• Cap the apex of the arytenoid cartilage

• Yellow, elastic cartilage serves to prolong them backward and medially

• Vestigial structures

Two cuneiform elastic

• Two elastic, elongated, wedge-shaped cartilages

• Vestigial structures

• Stiffen the aryepiglottic folds to maintain the laryngeal opening  

Cricoarytenoid

Permits rocking and gliding movement

• upward and outward

• downward and inward

Cricothyroid

Permits thyroid to rotate anteriorly or posteriorly on cricoid cartilage

Extrinsic ligaments and membranes of the larynx

• Hyoepiglottic ligament

• Hypothyroid (thyrohyoid) membrane

• Lateral hypothyroid ligament

• Middle hypothyroid ligament

• Cricotracheal membrane 

Intrinsic ligaments and membranes of the larynx

1. Conus elasticus (membrane/ligament): consists of anterior and two lateral portions

   1. Medial cricothyroid ligament

   2. Two lateral cricothyroid membranes/ligaments

2. Posterior cricoarytenoid ligament

3. Thyroepiglottic ligament 

Aryepiglottic folds

• Support tissue for maintaining the laryngeal opening

• Adjacent to the piriformis

Mucous membranes

Lines entire cavity or larynx, mouth, and pharynx

Stylohyoid

Pulls hyoid upward and backward

• Origin is base of skull at styloid process; insertion: hyoid

• Innervated by branch of CN VII

• Retracts and elevates process

Digastric muscles

Sling like belly at each end

• Anteriorly innervated by CN VII (mastoid process-hyoid)

• Raises hyoid bone or depresses the mandible 

Mylohyoid

Elevates hyoid

• Muscle sheet forming on floor of mouth, which tongue rests on

• Mandible-hyoid

• Innervated by CN V

• Elevates hyoid and laryngeal structures in general and tongue

• oriented between two sides of mandible and hyoid centrally

Geniohyoid

Pulls the hyoid up and forward

• Originates from internal surface of mandible

• Runs posteriorly and downward, inserting into anterior hyoid away from midline

• Innervated by CN XII

• Pulls hyoid up and forward

• Paired muscle

Sternohyoid

Depresses hyoid

• Originates in most superior surface of thorax at clavicle, inserts: hyoid

• CN XI

Sternothyroid

Depresses thyroid cartilage

•  Located close to midline of neck

• Originates at sternum, insert to thyroid at oblique line

• CN XII

Thyrohyoid

Depresses hyoid or elevates thyroid

• Thyroid (at oblique line) to hyoid (greater cornua) 

• CN XII

• Continuation of sternothyroid muscle

Omohyoid

Depresses, retracts, or pulls hyoid to one side or the other

• Two-bellied, two-directional from scapula to hyoid

• CN XII

Extrinsic muscles of the larynx

• Support of the larynx, fixing position

• One attachment is to non-laryngeal structure

• Suprahyoid muscles: elevate larynx or moves forward

  • Associated with mandible and tongue

Intrinsic muscles of the larynx

• Control of sound production

• Both attachments within larynx 

Lateral cricoarytenoid

• Regulates medial compression

• Supplied by recurrent laryngeal branch of CN X

• Draws arytenoids forward and medially, aids in rocking arytenoids, adducts vocal cords: adductor

• Connects cricoid with arytenoids

Transverse arytenoid

Draws arytenoids together (adducts) and regulates medial compression

• Part of “interarytenoid” group

• Supplied by recurrent laryngeal branch

• CN X

Oblique Arytenoid

Adducts arytenoids to regulate medial compression

• Part of “interarytenoid” group

• Supplied by recurrent laryngeal nerve CN X

Posterior Cricoarytenoid

Rocks arytenoid dorsally, abducting the vocal processes

• Antagonist of lateral cricoarytenoid

• Innervated by recurrent laryngeal nerve (CN X)

• Originates midline or cricoid lamina to posterior surface of arytenoids muscular process

Vocalis

• Tensor

• May be part of thyroarytenoid 

• Innervated by recurrent laryngeal nerve (CN X)

• Immediately flanks vocal ligament

• Angle of thyroid to vocal process of arytenoids

Cricothyroid

1. Found on outer surface of larynx

2. Cricoid cartilage to thyroid

3. Innervated by superior laryngeal nerve (CN X)

4. Elevates cricoid arch, depresses cricoid lamina

5. Lengthens and tenses VFs (tensor)

6. Related to pitch changes

Lateral thyroarytenoid

• Arises from lower portion of thyroid angle to vocal process and surface of arytenoids

• Supplied by recurrent laryngeal nerve (CN X)

• Draws arytenoids forward, shortens, and thickens VFs (relaxer)

Pharynges

• Made up of three walled spaces in vocal track

• Muscular tubes that contain air

• Divided into three parts

  • Nasopharynx (upper)

  • Oropharynx (middle)

  • Hypo/laryngopharynx (lower)

• Critical in modifying sound

• Taste/temperature sensation

Constrictor group

Narrows pharynx

• Superior:

  • Velopharyngeal

• Middle 

• Inferior:

  • Cricopharyngeal

  • Thyropharyngeal 

Levator group

Elevates pharynx

• Stylopharyngeal

• Salpingopharyngeal 

Cranial Nerves involved in phonation

• Trigeminal (CN V)

• Facial (CN VII)

• Glossopharyngeal (CN IX)

• Vagus (CN X)

• Hypoglossal (CN XII)

Three issues with direct observation of the larynx

1. Larynx is deep within neck and out of view

2. Interior of larynx is dark and must be illuminated for viewing

3. Vocal fold movement during phonation are too rapid for unaided eye

Myoelastic-aerodynamic theory of voice production

• First introduced by Johannes Muller in 1843

• Essence of theory is that glottal vibration is a result of the interaction between aerodynamic forces and vocal fold muscular forces

• Seven-step process of phonation 

Myoelastic-aerodynamic theory step 1

Vocal folds are abducted

• Diaphragm lowers

• Thorax expands

• Air is drawn into lungs because of pressure

Myoelastic-aerodynamic theory step 2

Vocal fold adduct (or partially adduct)

• Vocal fold involuntarily set proper length and tension for desired pitch

Myoelastic-aerodynamic theory step 3

Muscular and passive forces collapse lungs

• Air is forced out of the lungs

Myoelastic-aerodynamic theory step 4

Air slows at underside of adducted vocal folds

• subglottal air pressure rises

• air flow continues from lungs

Myoelastic-aerodynamic theory step 5

Air pressure overcomes strength of vocal fold adduction

• Vocal folds are blown apart

• Puff of air is emitted

• Airflow rate increases again while moving through glottis

Myoelastic-aerodynamic theory step 6

Subglottal pressure is reduced when first puff of air is emitted

• Elasticity and muscular condition of vocal folds and Bernoulli effect cause adduction to occur again

Myoelastic-aerodynamic theory step 7

Vocal folds should be symmetrical and consistent in weight and mass

• because of symmetry and consistency, the process can be repeated in a periodic manner as long as air is exhaled

Bernoulli Effect

• Bernoulli effect occurs when velocity of subglottal pressure increases while approaching and passing through constricted glottis; increased velocity creates negative pressure between and just below medial edge of vocal folds; vocal folds are drawn together because of negative pressure

Titze’s Cover Body Theory (1994)

• Complex vibratory patterns of phonation come from

  • Loose masses of vocal folds associated with cover (epithelium and superficial layer of the lamina propria)

  • Denser masses of vocal folds associated with transition/body (intermediate and deep layers of the lamina propria and vocalis muscle)

• Allows for multiple modes of phonation 

• The basic features of laryngeal adjustments to the different phonatory settings can be summarized as proposed by Hirose (1996)

  • Abduction or adduction of the vocal folds

  • Constriction of the supraglottal structures

  • Adjustment of length

  • Stiffness and thickness of the vocal folds 

  • Elevation and lowering of the larynx 

Cover

Epithelium and superficial layer of lamina propria

Transition

Intermediate and deep layer of the lamina propria

Body

Vocalis muscle

Medial Compression

• Vocal Intensity changing

  • As intensity increases, vocal folds remain closed for a longer time during vibratory cycle

    • Medial compression and laryngeal resistance to air flow increases

    • Forceful adduction of vocal folds accomplished by simultaneous contraction of the lateral cricoarytenoid and interarytenoid muscles

    • Increase in glottal tension accomplished by vocalis and cricothyroid muscles

  • With increased airflow subglottal pressure, intensity increases because greater medial compression, greater excursion from midline/greater amplitude

  • Modifying vocal intensity/loudness happens frequently during speech (this is a suprasegmental/prosodic feature)

Pitch Rising

• Acoustic: fundamental freq, perceptual: pitch

• Pitch changes primarily as a result of modifications in glottic tension and mass

• Pitch rising: vocal folds must vibrate more quickly; to do this, the folds get thinner by being stretched longer

• Cricothyroid muscle is contracted and rotated

  • VFs elongate by sliding of thyroid cartilage on the cricothyroid joint

  • An increase in pitch results from the antagonistic action of the cricothyroid and thyroarytenoid muscles

  • VFs make the finer adjustments

• Posterior cricoarytenoid: abductor that also increases gross tension

• Subglottal pressure may or may not increase 

Pitch lowering

• Decrease in tension or length and/or an increase in mass of vocal folds

• Thyroarytenoid muscle

  • Decreases the distance between the arytenoid and thyroid cartilages

  • Shortens and relaxes the vocal folds

• Medial compression/adduction partially relaxation facilitates by the lateral cricoarytenoid muscle

• We change pitch/intonation (suprasegmentals) frequently during speech 

Phonation

• Posterior portion (cartilaginous) vibrates less because of weight of vocal process in the folds

• Greatest excursion at juncture of anterior one third and posterior two thirds of VFs

  • Greatest amount of displacement from midline

• When VF length, tension, and medial compression are modified, acoustic and perceptual properties change 

• Two basic adjustments:

  • Medial compression

  • Longitudinal compression

• Primary factors affecting vibratory rate

  • Mass

  • Tension

• Pitch is dependant on

  • Frequency of VF vibration

  • Pattern of vibration

  • Configuration of vocal tract

• Divided into two phases

  • Prephonation phase

  • Attack phase 

Active longitudinal tension of the VFs

Contraction of the vocalis muscle

Passive longitudinal tension

Contraction of the cricothyroid muscle 

Medial compression is achieved by

Contracting the lateral cricothyroid muscles

Adductive tension caused by

Contraction of the interarytenoid muscles and the lateral cricoarytenoid muscles

Phonation phase

• Vocal folds move from an abducted to either and adducted or partially adducted position

• Subglottal pressure build and velocity of air is raised sharply

• Medial compression of vocal folds (varies depending on desired intensity) 

Attack phase

• Begins with VFs adducted though initial vibratory cycles

• Bernoulli effect (myoelastic aerodynamic theory)

• Highly variable in duration (depends on adduction/compression during pre-phonation)

Breathy

airflow starts before vocal folds vibrate

Glottal

Abrupt start to vocal fold vibration

Modal register

• Your normal speaking voice

• Pattern of phonation used most often

• Habitual pitch

• Most optimal

Whisper

No phonation

Glottal fry

• Creaky voice/”popcorn” quality/pulse register

• Vibrating vocal folds with very low frequency

• Vocal folds are strongly adducted with weak longitudinal tension 

Falsetto

Extreme upper portion of the pitch range

• Vocal folds stretched longitudinally

• Adduction of folds is high and the medial compression is also strong

Laryngeal whistle

• Escape of air between vocal folds

• Triangular opening of the cartilaginous glottis

• Adductive tension is very low and medial compression as well as longitudinal tension are moderately high 

Infant larynx

• Larynx is higher in the neck

• More than 50% of glottis is cartilaginous whereas two-thirds is muscles and tissue in adult

• Lower border of cricoid is between 2nd and 3rd cervical vertebrae

• Epiglottis touches the soft palate

• Hyoid bones and thyroid cartilage in direct contact with no space between them anteriorly 

Young larynx

• Larynx begins the initial descent at birth until age 5 (level of C6) and continues until 15 or 20 (reaches C7)

• No major differences in pitch and pitch range between and and girls prior to puberty

• In males during puberty, thyroid cartilage grows and VFs increase in length (10mm to 17-20mm total) and thicken

• In females, VFs also increase in length (4mm to 12.5-17mm total)

• VFs and mucosa begin to mirror an adult’s around age 16

• Thyroid angle more rounded in females, although no relationship between VF length and thyroid angle

Aging Larynx

• Adults: male and female voice, roughly an octave apart

• Vocal pitch lowers in females

  • Vocal folds thicken

• Vocal pitch raised slightly in males

  • Vocal folds thin

• Ossification and calcification of laryngeal cartilages

  • Cartilage becomes brittle