Isabel Villagar

Speaking and singing involve a voice mechanism that is composed of three subsystems. Each subsystem is composed of different parts of the body and has specific roles in voice production.

The ability to produce voice starts with airflow from the lungs, which is coordinated by the action of the diaphragm and abdominal and chest muscles.

The voice box (larynx) and vocal folds (sometimes called vocal cords) comprise the vibratory system of the voice mechanism.

The vocal tract is comprised of resonators which give a personal quality to the voice, and the modifiers or articulators which form sound into voiced sounds.

The key function of the voice box is to open and close the glottis (the space between the two vocal folds).

• Role in breathing: open glottis
  • Voice box brings both vocal folds apart during breathing.
• Role in cough reflex: close, then open glottis
  • Voice box closes the glottis to build up pressure, then opens it for the forceful expelling of air during cough.
• Role in swallowing: close glottis
  • Voice box coordinates closing the glottis by bringing both vocal folds to the midline to prevent choking during swallowing.
• Role in voice: close glottis and adjust vocal fold tension
  • Voice box brings both vocal folds to the midline to allow vocal fold vibration during speaking and singing.
  • Voice box adjusts vocal fold tension to vary pitch (how high or low the voice is) and changes in volume (such as loud voice production).

• Cartilages
• Muscles
• Nerves
• Vocal Folds

There are three cartilages within the larynx.

1. Thyroid Cartilage
   • Forms the front portion of the larynx
   • Most forward part comprises the "Adam's apple"
   • Houses the vocal folds
   • Vocal folds attach just below the Adam's apple
2. Cricoid Cartilage
   • Below the thyroid cartilage
   • Ring-like: front to back
   • Becomes taller in the back of the voice box
   • Platform for the arytenoid cartilages
3. Arytenoid Cartilages (left and right)
   • Pair of small pyramid-shaped cartilages
   • Connect with the cricoid cartilage at the back of the vocal folds
   • With the cricoid cartilage, forms the cricoarytenoid joint

Voice box muscles are named according to the cartilages to which they are attached.

• The brain coordinates voice production through specific nerve connections and signals
• Signals to the voice box for moving voice box muscles (motor nerves) come from:
  • Motor branches of recurrent laryngeal nerve (RLN)
  • Superior laryngeal nerve (SLN)
• Signals from the voice box structures for feeling (sensory nerves) travel through sensory branches of the RLN and SLN

Key Information

"Recurrent" laryngeal nerve: The recurrent laryngeal nerve is so named because on the left side of the body it travels down into the chest and comes back (recurs) up into the neck to end at the larynx. [see figure below]

Long path of left RLN: The circuitous path of the left RLN throughout the chest is one reason why any type of open-chest surgery places patients at risk for a recurrent laryngeal nerve injury, which would result in vocal fold paresis or paralysis. [see figure below] (For more information, see Vocal Fold Scarring and Vocal Fold Paresis / Paralysis.)

Shorter path of right RLN: The right recurrent laryngeal nerve continues in the upper chest and loops around the right subclavian artery, just behind the clavicle (collarbone), then travels the short distance in the neck to the larynx.

Diagram of Key Nerves for Voice Production

This diagram shows the "long path" of the left recurrent laryngeal nerve (left RLN). After it branches off the vagus nerve, the left RLN loops around the aortic arch in the chest cavity and then courses back into the neck. This long course makes it at higher risk for injury compared with the shorter course of the right RLN which does not run through the chest cavity. (click for larger image)

The left and right vocal folds are housed within the larynx. The vocal folds include three distinct layers that work together to promote vocal fold vibration.

1. Covering/mucosa: Loose structure that is key to vocal fold vibration during sound production; is composed of:
   • Epithelium
   • Basement membrane
   • Superficial lamina propria (SLP)
2. Vocal ligament: The vocal ligament is composed of:
   • Intermediate lamina propria
   • Deep lamina propria (contains collagen fibers that are stronger and more rigid than the superficial lamina propria)
3. Body: The vocal fold body is composed of the thyroarytenoid muscle. This muscle helps close the glottis and regulate tension of vocal fold during speaking and/or singing. The medial portion of this muscle is also called "vocalis muscle."

The vocal folds move similar to a car's windshield wipers that are attached to the middle of the windshield and open outwards. (See figure below.)

• The front ends of both vocal folds are anchored to the front-middle (anterior commissure).
• The back ends of both vocal folds are anchored to the arytenoid cartilages.
• When arytenoids are moved to the open position by the posterior cricoarytenoid muscle, vocal folds open, resulting in glottal opening.
• When arytenoids are closed by the lateral cricoarytenoid and inter arytenoid muscles, vocal folds are brought to the midline resulting in glottal closure.