News of Note
The Hyoid Bone is Connected to …
So far this year we have covered the basics of posture and the respiratory system and their role in singing. This month, before we go into the actual mechanics of phonation, I will present a simple overview of the anatomy of the vocal apparatus.
Anatomy is “the science of structure in plant and animals.” (Titze). The larynx or voice box houses the vocal folds and is comprised of several cartilages. The frontal piece, the thyroid cartilage, is made up of 2 plates that form an angle in the front, with a “V” notch at the top. You can actually feel this with your fingers. Theses plates curve around, leaving an opening in the back. Two horn-like projections on the back ends of both sides extend upwards and downwards beyond the thyroid cartilage. They are the superior and inferior cornu. The upper set connects to the hyoid, indirectly connecting the tongue to the larynx. (This information will be important in the upcoming issues when we delve into the actual process of sound making! )The lower protrusions attach to the cricoid thyroid cartilage. Unlike the thyroid cartilage, the cricoid cartilage is a ring-like structure, encircling the airway. It is actually the top most tracheal ring.
The two back corners of the cricoid thyroid cartilage are set up to accommodate the paired pyramid-shaped arytenoid cartilages. The arytenoids can swivel backwards, forwards and sideways. The vocal folds are attached to them and it is the arytenoids that are in part, responsible for the abduction and adduction of the folds, ie.,the opening and closing of them. A note here: as we age, these joints like others in our bodies, can suffer from arthritis which can cause breathiness in the sound from an incomplete adduction.
The tongue-shaped epiglottis, also a cartilage, has the job of preventing food from getting into the airway, by dropping down over the larynx. The food is directed to the esophagus which lies directly behind the trachea. The epliglottis attaches to the anterior inner surface of the thyroid cartilage, the hyoid bone and tongue base.
The horse-shoe shaped hyoid bone, also called the tongue bone, is the only bone among all these cartilages. It is connected to the larynx via the thyroid membrane and the superior cornu. This bone acts as a sort of grand central station as several muscles anchor here.
Now let’s look at some of the muscles that are involved in vocal production. The laryngeal muscles fall into two categories: intrinsic and extrinsic. The intrinsic muscles interconnect the interior components of the larynx, primarily working to control the act of phonation while the extrinsic muscles connect the larynx to the outside surrounding structures, supporting and stabilizing the larynx within its framework. The cricoid thyroid muscles runs from the front of the cricoid thyroid to the thyroid cartilage and the inferior cornu. They control pitch by elongating and tensing the vocal folds. Other muscle groups attach the arytenoids to the CT and assist in the opening and closing of the vocal folds. They are the lateral (adduction) and posterior (abduction) cricoid thyroid muscles. The interarytenoid muscles connect the 2 arytenoids to each other and are also adductors.
The extrinsic muscles include the infrahyoid and superhyoid groups which are composed of smaller muscle sub-groups. Per their name, these muscles hitch up to the hyoid bone. Each has their own specific function, ranging from depressing to elevating the larynx and depressing and retracting the hyoid, effecting tongue movement.
The vocal folds are comprised of 5 layers. The skin-like epithelium is the top layer. It helps to hold the shape of the vocal folds. It is made up of fluid-like tissue and measures approximately .05-.10mm thick. The next 3 non-muscular tissue layers, collectively, are called the lamina propria. These 3 layers are very important to the efficient workings of the vocal folds. The outer most layer of this group, the superficial layer, at .5mm thick, is made up of “loosely organized elastin fibers surrounded by interstitual fluids”. (Titze) Because of its stretching and elongation properties, elastin protein plays a big role in the vibration of the tissues that produce the sound waves necessary for phonation. It is similar to a rubber band and is responsible in large part for the important muscosal wave we will explore in later issues. It also assists in the regulation of longitudinal tension and relaxation of the vocal folds necessary for pitch change, and helps in closing the opening between the folds (the glottis). The intermediate layer contains both elastin and some collagen fibers making it a little less pliable. The deep and final layer of the lamina propria contains mostly collagen fibers whose protein structure limits elongation (which is why it is used in beauty skin creams!). Collagen fibers are similar to the consistency of cotton thread. These last two layers combined, are about 1-2mm thick. The paired thyroidarytenoid muscle (a reminder on how muscles are named: the point of origin, in this case the thryroid and the insertion point, the arytenoids.) at 7-8mm thick, makes up the bulk of the folds and is comprised of 2 sections, the vocalis muscle and the thryomuscularis.
Like other parts of the body, the larynx requires blood flow. This is supplied by arteries that branch off from the carotid artery. Innervation to the laryngeal muscles is provided by the superior and the recurrent laryngeal nerves, fed by the vagus nerve. Any injury or surgery to this area could affect the condition of these nerves and therefore, phonation.
I hope this brief anatomical overview of the vocal mechanism will come in handy throughout the year as we begin to explore the actual process of phonation.
Principles of Voice Production. Titze, Ingo. Prentice Hall. 1994 Speech and Hearing Science: anatomy and physiology. 4th ed. Zemlin, William. Allyn & Bacon. 1997. www.photosearch.com
May Vocal Opportunities
On Saturday, May 12th from 10-11am, I will once again be offering an “Introduction to Voice” class at the Waldo library through Communiversity. Enrollment is limited so if you are interested call 816-235-1448 to register.
A new beginning voice class will be starting Tuesday, May 22nd, 7-8pm. The cost of this 6 week course is $75. This is a great introductory class for those wanting to use their voices in a more effective and healthy manner, whether for singing or speaking. If you would like to know more, visit my website at www.revoice.biz or contact me at [email protected]
Don’t forget Mother’s Day! reVoice offers gift certificates that can be used towards private or group sessions. Contact me at [email protected] or 816-444-5089. A unique gift for Mom!