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The human voice is a fascinating instrument, and the muscles that control vocalization play a crucial role in our ability to communicate. The voice box, or larynx, is the star of this intricate process, housing the vocal cords (or vocal folds) that vibrate to produce sound. But what are the muscles behind this mechanism, and how do they work together to create our unique voices? From the diaphragm and chest muscles that initiate airflow to the complex interplay of intrinsic and extrinsic laryngeal muscles, the journey of vocalization is a symphony of muscular coordination. Let's delve into the fascinating world of these vocal muscles and explore their functions, interactions, and impact on our daily lives.
| Characteristics | Values |
|---|---|
| Muscle that controls vocalization | Vocal folds/cords, thyroarytenoid muscle, cricothyroid muscle |
| Location | Inside the voice box/larynx |
| Function | Produce sound, alter pitch and volume |
| Innervation | Recurrent laryngeal nerve, superior laryngeal nerve |
| Blood Supply | Superior and inferior thyroid arteries |
| Layers | Epithelial, lamina propria, muscular (including vocalis and thyroarytenoid) |
| Length | 6-8mm at birth, grows with age |
| Gender Differences | Testosterone thickens and lengthens male vocal cords during puberty |
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What You'll Learn
The role of the diaphragm and abdominal and chest muscles
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 diaphragm is the primary muscle of respiration, and it contracts and relaxes to facilitate inhalation and exhalation. During inhalation, the diaphragm contracts and flattens, which increases the volume of the chest cavity and draws air into the lungs. During exhalation, the diaphragm relaxes and returns to its dome-shaped position, which decreases the volume of the chest cavity and pushes air out of the lungs. This coordination of inhalation and exhalation by the diaphragm provides the necessary airflow for vocalization.
The abdominal and chest muscles also play a crucial role in vocalization by providing stability and facilitating breathing. The abdominal muscles, including the internal and external obliques, the rectus abdominis, and the transversus abdominis, help to stabilize the trunk and maintain a consistent airflow during vocalization. They work in conjunction with the diaphragm to control the volume and speed of airflow from the lungs. Additionally, the chest muscles, such as the pectoralis major and minor, intercostals, and serratus anterior, assist in expanding and contracting the rib cage, contributing to efficient inhalation and exhalation.
The diaphragm and abdominal and chest muscles work in harmony to regulate the airflow from the lungs, which serves as the foundation for vocalization. The diaphragm's contraction and relaxation, along with the stabilization and respiratory support provided by the abdominal and chest muscles, ensure a steady and controlled airflow. This airflow then passes through the vocal tract, which includes the voice box (larynx) and vocal folds (vocal cords).
The vocal folds, composed of various muscles and cartilage, vibrate due to the airflow from the lungs, producing the sound of the voice. The vocal fold body is made up of the thyroarytenoid muscle, which helps close the glottis and regulate vocal fold tension during speaking and singing. The vocalis muscle, part of the innermost muscular layer of the vocal folds, also contributes to vocal fold movement and tension. Additionally, the cricothyroid muscle lengthens and tenses the vocal folds, resulting in faster vibrations and higher pitch, while the thyroarytenoid muscle shortens and relaxes the vocal folds, leading to slower vibrations and lower pitch.
The intrinsic and extrinsic muscles of the larynx also play a significant role in vocalization. The intrinsic muscles, including the lateral cricoarytenoid, transverse arytenoid, posterior cricoarytenoid, oblique arytenoid, and cricothyroid muscles, govern vocal fold movement, tension, and abduction. The extrinsic muscles, such as the sternohyoid, omohyoid, sternothyroid, and thyrohyoid muscles, attach to the hyoid bone and move the thyroid cartilage, lowering the larynx and influencing vocal fold vibration.
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The vocal ligament and vocal fold body
The vocal ligament is the medial edge of the laryngeal triangular membrane, also called the conus elasticus. The vocal ligament forms from the free upper edge of the cricothyroid ligament. The vocal fold body is composed of the thyroarytenoid muscle, which helps close the glottis and regulate vocal fold tension during speech and song. The medial portion of this muscle is also called the vocalis muscle. The thyroarytenoid muscle is the most internal portion of the large thyroarytenoid muscle lying externally to the laryngeal quadrangular membrane. The vocal ligament is the elastic component of the vocal fold, which is important for producing vibrations of the expiratory airflow and, consequently, for the generation of specific sound frequencies. The thyroarytenoid muscle regulates the tension of the vocal folds, which is commonly accepted to be critical for sound production, pitch, and speech in humans.
The vocal folds are intrinsic parts of the composite laryngeal structure. They are two tissue folds stretched between the internal anterior angle of the thyroid cartilage and the vocal process of the arytenoid cartilages. The vocal folds appear as two white and shiny ribbons, which, in phonation, are adducted, i.e., the free edge of both folds come into contact. During respiration, they abduct to permit the free flow of inspiratory and expiratory air volumes. The vocal folds are relatively avascular, and appear white in colour. The space between the vocal folds is known as the rima glottidis. The vestibular folds (false vocal cords) lie superiorly to the true vocal cords. They consist of the vestibular ligament (free lower edge of the quadrangular membrane) covered by a mucous membrane, and are pink in colour.
The length of the vocal folds in humans varies between 10 mm for females and 16 mm for males. The vocal ligament is composed of the intermediate and deep layers of the VFLP, with a mean thickness between 1 mm and 2 mm. The vocal fold body is composed of the thyroarytenoid muscle, which is also called the vocalis muscle in its medial portion. The thyroarytenoid muscle regulates the tension of the vocal folds, which is critical for sound production, pitch, and speech.
The vocal folds move similar to a car's windshield wipers that are attached to the middle of the windshield and open outwards. 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.
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The role of the thyroarytenoid muscle
The thyroarytenoid muscle is a broad, thin muscle that forms the body of the vocal fold and supports the wall of the ventricle and its appendix. It is one of the intrinsic muscles of the larynx, along with the oblique arytenoid, transverse arytenoid, posterior cricoarytenoid, lateral cricoarytenoid, cricothyroid, aryepiglotticus, and thyroepiglottic muscles. These muscles work together to regulate the length and tension of the vocal folds.
The thyroarytenoid muscle arises from the inner surface of the inferior part of the thyroid cartilage and the cricothyroid ligament. Its fibres pass backward and laterally, inserting into the base and anterior surface of the arytenoid cartilage. The lower and deeper fibres of the muscle can be differentiated as a triangular band that inserts into the vocal process of the arytenoid cartilage. This portion is called the Vocalis and lies parallel to the vocal ligament.
The thyroarytenoid muscle has two main functions: drawing the arytenoid cartilages forward toward the thyroid, thus relaxing and shortening the vocal folds; and rotating the arytenoid cartilages inward, which helps close the rima glottidis by bringing the two vocal cords together. This closure is crucial for sound production or phonation, as it allows the vocal folds to oscillate and produce sound.
The thyroarytenoid muscle also plays a role in controlling pitch. While the cricothyroid muscle increases the length and tension of the vocal folds, leading to a higher-pitched sound, the thyroarytenoid muscle shortens the vocal folds. Interestingly, canine studies have found that isolated thyroarytenoid activation actually raises the pitch, although less steeply than cricothyroid activation.
The complex structure and multiple points of attachment of the thyroarytenoid muscle enable it to perform these two distinct actions simultaneously. This muscle is supplied by the laryngeal branches of the superior and inferior thyroid arteries and drained by the internal jugular vein via the superior and inferior laryngeal veins.
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The cricothyroid muscle and vocal fold vibration
The ability to produce voice starts with airflow from the lungs, which is coordinated by the diaphragm and abdominal and chest muscles. The voice box (larynx) and vocal folds (vocal cords) comprise the vibratory system of the voice mechanism. The vocal folds must be held in the midline of the glottis for vocal fold vibration to occur during voice production.
The cricothyroid muscle is the only tensor muscle of the larynx aiding with phonation. It is a fan-shaped muscle situated at the outer surface of the larynx. Its action tilts the thyroid cartilage forward to help tense the vocal cords, thus increasing the pitch of the voice. The cricothyroid muscle increases the angle between the cricoid and thyroid cartilages, thus elongating the vocal folds to increase tension and the rate of vibration. This results in a higher pitch.
The thyroarytenoid muscle fibers help form the muscular layer of the vocal cord. The medial portion of this muscle is also called the vocalis muscle, which forms the vocal ligament. The vocal ligament is the free edge of the cricothyroid ligament. The thyroarytenoid muscle contraction brings the arytenoids closer to the thyroid cartilages, thus shortening and relaxing the vocal fold and allowing for a lower pitch.
The interaction of the cricothyroid and thyroarytenoid muscles can produce different stress conditions in the vocal folds and different voice types. Vocal fold eigenfrequencies are primarily determined by vocal fold stiffness. With strong cricothyroid activation and an elongated vocal fold, increasing thyroarytenoid contraction reduces the degree of vocal fold elongation and thus reduces vocal fold eigenfrequencies.
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The interaction of intrinsic and extrinsic muscles
The ability to produce voice starts with airflow from the lungs, which is coordinated by the diaphragm and abdominal and chest muscles. The voice box (larynx) and vocal folds (vocal cords) comprise the vibratory system of the voice mechanism. The vocal folds are controlled by intrinsic and extrinsic muscles.
The intrinsic laryngeal muscles act on the individual components of the larynx. They control the shape of the rima glottidis (the opening between the vocal folds and the arytenoid cartilages), and the length and tension of the vocal folds. The intrinsic muscles of the larynx are classified as adductors (vocal fold closing) or abductors (vocal fold opening). The adductor group includes the lateral cricoarytenoid and transverse arytenoid muscles, while the posterior cricoarytenoid muscles govern abduction. The cricothyroid muscle, also known as the 'singer's muscle', is responsible for tensing the vocal cords. The thyroarytenoid and vocalis muscles relax the vocal cords.
The extrinsic laryngeal muscles, on the other hand, change the position of the larynx in the neck by raising or lowering the thyroid cartilage. The suprahyoid and infrahyoid muscles, along with the stylopharyngeus, comprise the extrinsic muscles. The suprahyoid muscles and stylopharyngeus elevate the larynx, while the infrahyoid muscles depress it.
Most functions involving the larynx require the coordination of both intrinsic and extrinsic muscle groups. Honda et al. (1999) demonstrated that the interaction between the intrinsic CT muscle and the extrinsic sternothyroid muscle influences the fundamental frequency of vocal fold vibration. The CT muscle increases the angle between the cricoid and thyroid cartilages, elongating the vocal folds and increasing tension and vibration rate. Conversely, the sternothyroid lowers the larynx, reducing the angle between the cartilages, shortening the vocal folds, and lowering the frequency of vibration.
The complex interaction of intrinsic and extrinsic muscles allows for precise control of vocal fold movements, enabling the production of a wide range of sounds, from speech to singing.
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Frequently asked questions
Vocal cords, or vocal folds, are two muscular bands inside your voice box that vibrate to produce the sound of your voice.
The intrinsic muscles of the larynx alter the length and tension of the vocal cords. The adductor muscle group includes the lateral cricoarytenoid and transverse arytenoid muscles, while the posterior cricoarytenoid muscles govern abduction. The cricothyroid muscles tense the vocal cords, and the thyroarytenoid and vocalis muscles relax them.
The vocal cords vibrate when air passes between them, reducing the pressure between them (the Bernoulli effect). The vocal cords vibrate faster when they are longer, thinner, and more taut, and slower when they are shorter, thicker, and floppier.
The cricothyroid and thyroarytenoid muscles coordinate with each other to create different pitches. They can also work together to produce the same pitch with a different sound quality. The length and thickness of the vocal cords help determine the pitch, with thicker vocal cords producing a lower pitch.
