Anatomy and Physiology of the Vocal Mechanism

Suprahyoids

Extrinsic laryngeal muscles

Above the hyoid bone

Function: elevate larynx via hyoid elevation

Attachment and function of intrinsic laryngeal muscles

Both attachments are with in the larynx

Function: modify the position, tension, and edge of the true vocal folds

Innervation of the ESLN (external superior laryngeal nerve)

Cricothyroid muscle (CT) for motor function

Function of the cricothyroid (CT)

To increase pitch in high register phonation by tensing/thinning the vocal folds

What is the function of the ISLN (internal superior laryngeal nerve)?

Laryngeal sensation above the true vocal folds

Muscles innervated by the RLN (recurrent laryngeal nerve)

Thyroarytenoid (TA)

Lateral cricoarytenoid (LCA)

Interarytenoid (IA)

Posterior cricoarytenoid (PCA)

Motor function of the RLN (recurrent laryngeal nerve)

Vocal fold ab/adduction

Laryngeal adductors

Thyroarytenoid (TA) "rock"

Lateral cricoarytenoid (LCA) "rotate"

Interarytenoid (IA) "glide"

Posterior cricoarytenoid (PCA)

The only vocal fold abductor muscle

Innervated by the RLN

Positioned between the arytenoid complexes to the posterior cricoid cartilage

Vocal fold epithelium

Most external layer of the true vocal folds

Stratified squamous cells

Thinnest, only about 6-8 cells thick

Very pliable

Covered in slippery mucus lubrication for best vibration, hydration, and chemical balance

Delicate and receives first exposure to environmental influences (e.g. humidity, dehydration, pollution, reflux)

Lamina propria

2nd layer under the vocal fold epithelium

Superficial layer/Reinke's space, then intermediate, then deep layer

When do the length of the true vocal folds begin to differ between males and females?

Age 10

Presbylaryngeus

Aging voice

Voice quality, pitch, loudness, range, and endurance often decreases

Primarily due to vocal fold thinning/bowing/muscle atrophy

What changes occur as the vocal folds atrophy with age?

Loss of bulk in the lamina propria

Stiffness/fibrosis due to breakdown of collagen and elastic

Apoptosis

Reduced nerve supply to maintain muscle fibers

What is the primary factor leading to pitch lowering for males during puberty?

Testosterone

Requirements for voicing

Balance and coordination of respiration, phonation, and resonance

Breath support

How much air someone can fit in their lungs and generating appropriate airflow

Breath control

Regulating and coordinating airflow for speech and voice production

What structure does the trachea share a wall with?

The posterior wall of the trachea (e.g. the open part of the C) is shared with the anterior wall of the esophagus

Carina

Inferior aspect of the trachea

Location of split into the L and R mainstem bronchi

Structures of the lower respiratory system

lungs, trachea, bronchi, bronchioles, alveolar sacs

Structures of the upper respiratory system

Larynx, pharynx, nasal cavity

What structures are separated by the diaphragm?

thoracic and abdominal cavities

Inspiration

Diaphragm contracts: flattens to make the thoracic cavity longer while inhaling

External intercostals contract to pull the rib cage up and out, expanding the rib cage

Many different accessory muscles involved in expanding the rib cage

Expiration

Recoiling

Diaphragm goes back to resting position

Internal intercostals running between the ribs depress the rib cage and contract the thoracic cavity

Pressure inside lungs is high -> airflow wants to flow out passively

Abdominal and oblique muscles also involved in the recoil

More active process for speech compared to life (passive)

If the hyoid bone is chronically elevated, what may the larynx experience?

Increased muscular tension from the suprahyoids

What laryngeal cartilage is the Adam's apple part of?

The thyroid notch is the anterior-extending portion of the superior thyroid cartilage

What structure is below the cricoid cartilage?

The first tracheal ring

What are the 2 joints in the larynx + their purpose?

cricothyroid joint: articulates with activation of the cricothyroid muscle for high pitch phonation

cricoarytenoid joint: arytenoids rotate within the cricoid cartilage for vocal fold ab/adduction

Where is the vocal process and what happens there?

where the vocal fold vibratory edge meets the arytenoid cartilage

membrane meets cartilage

posterior-most portion of the vocal fold

Directional reminders when looking at the larynx

You're looking at them from the top

L and R are flip-flopped

Anterior is the bottom of the screen

Posterior is the top of the screen

Superior is toward the viewer

Inferior is deeper within the picture

abducted

true vocal folds are open/away from midline

adducted

true vocal folds are closed/toward midline

What are the 3 required items for the Aerodynamic-Myoelastic Theory of Phonation?

Muscular force for medialization of the vocal folds

Elastic recoil of the true vocal folds

Aerodynamics: positive and negative pressure

self-sustaining oscillation

true vocal folds continuing to independently phonate via the interaction of continuous airflow on adducted vocal folds, building up subglottic air pressure, and elastic recoil + negative pressure bringing the vocal fold edges back together

source

location of vocal fold vibration (aka true vocal folds)

filter

the vocal tract reinforcing or prolonging acoustic waves from the vocal fold vibration via how the wave reflect off the vocal tract structures

vocal tract structures

pharynx

oral cavity

nasal cavity

tongue

teeth

velum

uvula

hard palate

When do the vocal fold layers differentiate?

2-5 months: 2 layers

around 11 months: 3 layers

12-13 years: 5 layers