The Larynx: Structure and Function
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Most singers and speakers are aware of the existence of the larynx, colloquially known as the ‘voice box’, but understand very little about its structure and function, and the role of the vocal folds, (formerly called ‘vocal cords’), in voice production and in the creation of pitch. While I don’t believe that it is necessary for a singer to memorize all the parts and functions of the individual structures within the throat – we can leave that for the medical students - I do believe that gaining a better understanding of how the larynx works and what the vocal folds are and do can help a student of voice achieve technical proficiency and maintain vocal health.
My intention in this section is to provide some basic information about the highly complex structure of the larynx, and how the primary structures of the larynx affect vocal function. I’ll attempt to make descriptions and explanations as succinct and as clear as possible, and focus only on the principle cartilages, joints, bones, ligaments and muscles that help to produce the voice. However, given that the parts that make up the larynx are intricate and function in unique ways, and given that scientific and/or medical terms are sometimes the best ones (or the only ones) to use when discussing human anatomy, it may be impossible to truly simplify everything as much as I would like to. My suggestion is that singers thoroughly read the following sections and attempt to understand and learn whatever they can. Again, what is most important is that the student of voice gains a glimpse into the fascinating and complex – far more complex than any other instrument - structure that produces the voice and comes to develop a better appreciation for his or her built-in instrument.
Anatomy of the Vocal Tract
from the 20th U.S. edition of Gray's Anatomy of the Human Body
Posterior View Of Anterior Wall Of Larynx
Dorland's Medical Dictionary for Health Consumers. © 2007 by Saunders, an imprint of Elsevier, Inc. All rights reserved.
The vocal folds, together with the muscles and cartilages that support them, are known as the larynx.
The larynx is an organ in the neck that lies in front of the fourth, fifth, and sixth cervical vertebrae. It is situated just below where the tract of the pharynx (the part of the neck and throat situated immediately behind the mouth and nasal cavity, and above the esophagus, larynx, and trachea) splits into the trachea (the ‘windpipe’ or tube that allows the passage of air into the lungs) and the esophagus (a muscular tube through which food passes from the pharynx to the stomach). The larynx is involved in both the protection of the trachea and in the production of sound.
The upper entrance of the larynx – that which is continuous with pharynx - is a triangular opening that is narrow in front and wide behind, and slants downward and backward. The lower portion is continuous with the trachea and is circular. It is bordered in front by the epiglottis behind, by the arytenoid cartilages, the corniculate cartilages, and the interarytenoid notch (the indentation of the posterior portion of the aditus laryngeal inlet between the two arytenoid cartilages); and on either side, by the aryepiglottic fold, on the posterior part of the margin of which the cuneiform cartilages form a whitish prominence called the cuneiform tubercle. These folds form the upper borders of the quadrangular membrane.
Spaces of the Larynx
The image above shows the spaces created by the various structures of the larynx.
The first space in the larynx is called the vestibule, which is the space above the vestibular fold (false vocal fold). Just beneath the vestibular fold is the ventricle (not shown), which extends laterally and is connected anteriorly to a small sac called the saccule (also not shown). The saccule has special cells that produce a secretion to keep the vocal folds moist. Beneath the ventricle is the true vocal fold that extends from the vocal process of the arytenoid cartilages to the backside of the thyroid cartilage.
The larynx is connected with the pharynx by the opening or thin space between the right and left vocal folds and the arytenoid cartilages, called the glottis (or rima glottidis or rima glottides), through which air must pass in order to vocalize and breathe. The part between the arytenoid cartilages is called the intercartilaginous part (or the intercartilaginous glottis, respiratory glottis, or interarytenoid space), and the part between the vocal folds is called the intermembranous part (or glottis vocalis). The rima glottidis is closed by the lateral cricoarytenoid and arytenoid muscles, and its entrance is protected by the epiglottis.
The area below the glottis is called the infraglottic cavity (or infraglottic space). Below the infraglottic cavity is the trachea (“windpipe”).
The larynx consists of four basic anatomic components: a cartilaginous skeleton, intrinsic muscles, extrinsic muscles, and a mucosal lining.
Skeleton of the Larynx (Anterolateral View)
Skeleton of the Larynx (Posterior View)
The skeleton of the larynx is made up of the hyoid bone and several cartilages. There are nine cartilages of the larynx, three of which (the thyroid, the cricoid and the epiglottis) are unpaired, and three of which (the arytenoids, the corniculates, and the cuneiforms) are paired. These cartilages support the larynx and form its skeleton. They are connected to other structures of the head and neck through the extrinsic muscles. (The intrinsic muscles of the larynx alter the position, shape and tension of the vocal folds.)
The hyoid bone is a horseshoe-shaped (or U-shaped) bone situated in the anterior midline of the neck between the chin and the thyroid cartilage. At rest, it lies at the level of the base of the mandible (lower jaw) in the front and the third cervical vertebra behind. It is the only bone in the human skeleton that does not make contact with, or connect to, any other bone. The hyoid bone is not technically part of the larynx, though it is connected to it – to the thyroid cartilage - by the thyrohyoid membrane, and is held in place by the thyroid ligaments. The hyoid bone provides attachment to the muscles of the floor of the mouth and the tongue above, the larynx below, and the epiglottis and pharynx behind. It allows a wider range of tongue, pharyngeal and laryngeal movements by bracing these structures alongside each other in order to produce variation. During swallowing, the hyoid bone elevates, (also pulling the larynx upward with it), in order to guard the entrance of the airway against the introduction of food and other swallowed matter.
The cartilaginous skeleton refers to the cartilage structure in and around the trachea that contains the larynx, or houses the vocal folds, (which used to be called the ‘vocal cords’). It is comprised of the thyroid, cricoid, and arytenoid cartilages.
The thyroid cartilage is the largest of the nine cartilages that make up the laryngeal skeleton. It is attached to the hyoid bone and is made up of two plate-like laminae (thin cartilages) that fuse on the anterior (front) side of the cartilage to form a peak, lump or protrusion called the laryngeal prominence, (otherwise known as the Adam's apple). The angle of the thyroid cartilage surrounding the larynx is usually more acute in adult males - the two laminae of the thyroid cartilage that form the protrusion meet at an average of 90°in males, as opposed to 120°in females - and is therefore more pronounced. The thyroid cartilage forms the bulk of the anterior wall of the larynx, making up the body of the larynx, and serves to protect the vocal folds, which are located directly behind it. It also serves as an attachment for several laryngeal muscles.
The lip of the thyroid cartilage just superior to the laryngeal prominence is called the superior thyroid notch, while the notch inferior to the thyroid angle is called the inferior thyroid notch. Its posterior border is elongated both inferiorly and superiorly to form the superior horn of thyroid cartilage and inferior horn of thyroid cartilage. The inferior horns articulate with (connect with or come in contact with) the sides of the cricoid cartilage – see next paragraph - and form the cricothyroid joint, where the thyroid cartilage rocks back and forth, or pivots, at this point.
The cricoid cartilage is the only complete cartilaginous ring of the larynx and is the strongest of all the laryngeal cartilages. It is made of hyaline cartilage, (consisting of a slimy mass of a firm consistency, but of considerable elasticity and pearly bluish color), and can become calcified or even ossified, particularly in old age. It is shaped like a signet ring with a broad arch (the cricoid arch) on its posterior side - where it forms a square-shaped lamina (the cricoid lamina). As it extends upward to form the posterior border of the larynx, it tapers anteriorly to a narrow arch. Its anterior part is called the band. The cricoid is attached to the top of trachea, to the first tracheal ring, by the cricotracheal ligament. The cricoid cartilage provides attachments for the various muscles, cartilages, and ligaments involved in opening and closing the airway and in speech production.
The epiglottis is a large, leaf-shaped flap of elastic cartilage tissue that is attached to the root of the tongue and inferiorly to the thyroid cartilage by a small stem. During breathing, the epiglottis is pointed upward to allow air to freely enter and exit the trachea and lungs. During swallowing, however, the backward motion of the tongue forces the epiglottis over the laryngeal opening – it folds down into a horizontal position like a lid - to prevent swallowed material from entering the larynx and lungs, which would produce irritation and a strong cough reflex. The larynx is also pulled upwards with the elevation of the hyoid bone to assist this process.
The arytenoid cartilages are triangular (or pyramidal) pieces of mostly hyaline cartilage that sit on top of the cricoid lamina, posteriorly, and articulate there at the cricoarytenoid joints. The arytenoid cartilages slide and rotate on an axis at these joints. The movements that take place between the arytenoid and cricoid cartilages – that is, at the cricoarytenoid joints - include adduction (drawing together), abduction (pulling apart), anterior-posterior sliding, and medial-lateral sliding.
The triangular base of the arytenoid cartilages contains three processes: the vocal process, the muscular process, and a third process that is not well defined. The anterior angle of the base of the arytenoid cartilage – the medial process - is called the vocal process. It projects horizontally forward and gives attachment to the vocal ligament (vocal fold), which extends from the vocal process to the backside of the thyroid cartilage. Of the paired cartilages, the arytenoid cartilages are the most important because they influence the position and tension of the vocal folds. Any movement of the arytenoid cartilage will have an effect on the vocal folds (e.g., making them loose or taut, bringing them together or spreading them apart). The muscular process of the arytenoids – the lateral process - lies laterally, and most of the muscles that act to abduct (open) or adduct (close) the vocal folds attach to it. The arytenoid cartilages are pulled towards each other (approximated) by the transverse arytenoid muscle.
The paired corniculate cartilages are two small conical (or horn-shaped) nodules consisting of pieces of hyaline (yellow elastic) cartilage that articulate with the apex (summits) of each arytenoid cartilage, and serve to prolong them posteriorly and medially. They are situated in the posterior parts of the aryepiglottic fold, and are sometimes fused with the arytenoid cartilages.
The paired cuneiform cartilages are small, elongated, club-shaped pieces of yellow elastic cartilage located anterior to the corniculate cartilages. On the posterior part of the margin of the aryepiglottic fold, just in front of the arytenoid cartilages, they form a whitish prominence on the surface of the mucous membrane called the cuneiform tubercle.