How the voice works

The human voice is more than just the vocal folds (vocal cords is also used for the same set of tissues). At its most basic level, the voice relies on a power source (breath flow), a transducer (vocal folds) for converting that aerodynamic energy into acoustic energy, and an assortment of resonators (vocal tract, mouth, throat, tongue, lips, nasal passages) to modify (filter) that acoustic signal into words, colors, and meaning.

This process is further complicated by having inputs from health, disease, energy level, content (meaning), and intent (emotions). And because the tissues of the human voice are multifunctional, they must also take care of respiration, swallowing, and sphincter control. We all know how the system can break down if someone tells a joke while you are swallowing! It’s actually quite amazing how we learn to make use of all these functions and tissues without direct training.

So if we are to better understand this complex instrument we can take one of two approaches;

  • learn all about the individual components, or
  • work from the top down with the intent of shaping the outcome of their interactions.

This latter perspective is usually most useful in voice teaching and voice therapy. In fact it’s necessary. If you tell someone to increase the contractile force of their thyroarytenoid muscles by 20%, you’ll achieve only confusion, whereas if you ask the person to add some depth to the sound you stand a better chance of achieving that end. However, understanding the biomechanics of this instrument is crucial knowledge for a teacher. It can also allow the performer to have a better idea of what might be happening when their voice is ‘off.’Larynx from behind

 

Architecture of the larynx

The larynx is comprised of several cartilages and one bone. If you learn the names of these, all the connecting muscles and tissues are easy.Laryngeal cartilages

 

thyroid cartilage – This is the most prominent structure of the larynx. The other structures connect to this, even though it simply ‘floats’ between the trachea and the jaw. It houses and provides protection to the vocal folds. thyroid jpegIt’s most easily identifiable structure is the thyroid notch, or Adam’s apple, along its top middle edge. When you swallow, the larynx is elevated approximately (~) 25mm for men and 18mm for women. This allows the bolus (food and liquid) to pass into the opening of the esophagus. The thyroid cartilage is comprised of two plates (laminas) that join in the front, but are open in the back.

cricoid cartilage – The thyroid cartilage sits loosely on top of the cricoid cartilage. The cricoid cartilage can be thought of as the topmost ring of tracheal cartilage, except that it completes the circumference of the trachea with a large portion at the back of the larynx. Cricoid cartilageA flexible connection between the cricoid and thyroid cartilages is important for swallowing, and even more so for one of evolution’s most beautiful features – pitch change.

arytenoid cartilages – This pair of triangular, tooth-shaped cartilages sit on facets at the rear of the cricoid cartilage. This cricoarytenoid joint is alluvial, which allows the arytenoids to rotate and translocate (slide). All of the internal laryngeal muscles (except the cricothyroid (CT)) attach to these little cartilages. So we watch them carefully when viewing the larynx in the clinic for signs of abnormal movement.

hyoid bone – This is the only bone in the human body Hyoid_bone_-_close-up_- animation-by Animatography that is not connected to another bone. This ‘wishbone” is suspended from the jaw, tongue, and skull by 4 sets of muscles, and the rest of the larynx is suspended from it by 4 sets of muscles.