AERODYNAMIC MYOELASTIC THEORY
First introduced in 1843 by Johannes Muller AERO - air pressure and ow DYNAMIC - movement and change MYO - muscular involvement ELASTIC - ability to return to original state Consider how these are involved in voice production... Steps in MYOELASTIC AERODYNAMIC Theory STEP ONE
Diaphragm lowered Chest cage expanded Air drawn in lungs Vocal folds are open
Steps in MYOELASTIC AERODYNAMIC Theory
STEP TWO
Vocal folds are closed Vocal folds set to involuntarily proper length and tension for desired pitch by contraction of ve laryngeal adductor muscles
Steps in MYOELASTIC AERODYNAMIC Theory
STEP THREE
Muscular forces collapse lungs Air is forced out of the lungs
Through the bronchi Up the trachea
Steps in MYOELASTIC AERODYNAMIC Theory
STEP FOUR
Air slows at underside of vocal folds Air pressure increases
Air ow increases
Steps in MYOELASTIC AERODYNAMIC Theory
STEP FIVE
Air pressure overcomes strength with which the vocal folds are held together Vocal folds are blown apart Puff of air is emitted Airow rate increases again Complete obstruction not necessary to initiate phonation
A space of 3 mm & minimum airow will cause vibration
Steps in MYOELASTIC AERODYNAMIC Theory
STEP SIX
Subglottal pressure reduced when the rst puff of air is emitted Elasticity and muscular conditions of vocal folds and Bernoulli Effect cause adduction to occur again
Steps in MYOELASTIC AERODYNAMIC Theory
BERNOULLI EFFECT
Occurs when velocity of subglottal pressure increases while approaching and passing through constricted glottis Increased velocity creates negative pressure between and just below the medial edge of the vocal folds Vocal folds are drawn together because of the negative pressure
Steps in MYOELASTIC AERODYNAMIC Theory
STEP SEVEN
Vocal folds are symmetrical and consistent in weight and mass Because of symmetry and consistency, the process can be repeated in a periodic manner as long as air is exhaled
Vocal Production
Entire vocal fold vibrates in normal phonation
Greatest excursion occurs at juncture of anterior 1/3 and posterior 2/3 of vocal folds
Greatest amount of displacement from midline
Posterior portion (cartilaginous portion) vibrates less because of weight of vocal process in the folds
The Functions of the Larynx
Matthew Reeve The larynx is often described as the voice box. This label can be misleading as the larynx is not only a source of vocal sounds but it also has several other biological functions that are vital to survival. Knowledge and understanding of these functions help vocalists to use their voices safely and skilfully. Protection of the airways. The need to keep the airways free from obstruction is paramount to survival. This is considered the primary function of the larynx. The true vocal folds, false vocal folds and epiglottis act together as a sphincter to form a barrier that prevents food and foreign bodies entering the trachea and impeding respiration. A demonstration of the importance of this primary function is seen in there being three sets of muscles in place to close and tense the true vocal folds but only one set to open. The larynx reacts violently when stimulated by foreign objects consider how the body responds when food goes down the wrong way. This is a natural reex and happens as part of swallowing. Pressure valving. The ability to control pressure in the thoracic cavity is important for the efciency of bodily functions. These include going to the toilet, childbirth and the ability to secure the thoracic cavity when lifting heaving objects. In pressure valving larynx closure helps to stabilise the upper body, providing a solid framework for strenuous muscular effort. Do the following and notice what can happen at the larynx: sit on a chair and raise your feet off the ground; then, whilst seated, inhale and try lifting yourself and the chair off the ground. You feel a sense of closure at the larynx as the physical effort is exerted. Phonation. On the biological survival scale, phonation is considered a tertiary function. Like with other mammals, the larynx has evolved to assist with noise-making. The larynx is designed to enable crying and shouting with ease a baby can cry loud and long. Human larynxes have descended lower in the vocal tract compared to other mammals; this has facilitated more complex communication patterns. Singers and speakers capitalise on the phonatory ability of the larynx with complex linguistic tasks such as speech and song. The protective instincts of the larynx are easily triggered; they are wired into our ight and ght responses. Two of the natural functions of the larynx are reex actions that involve constriction the
of laryngeal structures, that is closure of the airway. For instance, if something goes wrong in a rehearsal and we get upset or angry, the protective reex can be triggered, and the larynx may constrict. This will clearly impede on vocal function. Active measures are needed to counteract what is biologically normal when singing or speaking in stressful situations. SOUND: Sound is generated when air is moved to cause variations in air pressure. The variations then travel through the air as sound waves. These variations of air pressure are then picked up by the ear and interpreted by the brain. Something has to move or vibrate in the rst place to cause the air to be displaced. Movement energy, or kinetic energy, is changed to acoustic energy. The environment can affect the properties of the sound waves as they travel to the ear.
Larynx
interface between the pharynx and the trachea (and respiratory tree). Shorter than pharynx, epiglottis at top primary function to keep the airway patent. secondary function the production of sound in phonation (1) Laryngeal Skeleton 3 single cartilages (1) epiglottis-thin, leaf shaped cartilage, located posterior to the root of the tongue. (2) thyroid cartilage two lamina that form Adams apple (3) cricoid- shaped like a signet ring, most inferior cartilage, articulates on its lateral surface with the inferior horns of the thyroid cartilage in a synovial jointernal 3 paired cartilages (1) Arytenoid cartilages- pyramidal in shape, articulate with the lateral parts of the lamina of the cricoid cartilage. Vocal process attaches the vocal ligament, narrowest portion of airway Muscular process attaches muscles (2) Corniculate- in the Quadrate membrane (makes up the vestibule of the larynx) (3) Cuneiform- sit on top of cricoid cartilages, synovial joints, slip back and forth, allow movement of vocal cords. (2) Membranes Larynx is suspended from the hyoid by the thyrohyoid membrane Conus elastus made of three ligaments, an elastic membrane that extends from the cricoid to the vocal ligaments. Cricothyroid ligament connect the arch of the cricoid cartilage with the thyroid cartilage Median cricothyroid ligament soft spot inferior to the thyroid cartilage where airway is closest to the skin Vocal ligament- forms the skeleton of the vocal fold Quadrangular membrane from the epiglottis to the arytenoid cartilages, lies superior to the vocal cords. The free inferior edges of the quadrangular membrane is the vestibular ligament or false cords (sup to real cords) Cricotracheal ligament connects the cricoid with the 1st tracheal ring (3) Glottis Definition The two vocal cords and the space between them. The functional larynx concerned with voice production Rimi glottidis the space between the vocal cords. (4) Muscles
Posterior cricoarytinoid muscles- CN X, pulls the muscular processes together abduct the vocal cords Lateral cricoarytinoid -adduct the vocal cords Cricothyroid only outside muscle innervated by superior laryngeal nerve (X) (5) Nerves Vagus Superior laryngeal nerve 2 branches (1) external branch motor to the cricothyroid and to the cricopharyngeus portion of the inferior constrictor (2) internal branch sensory to the interior of the larynx to the level of the subglottic space Recurrent laryngeal nerve motor to all muscles of larynx (except cricothyroid) sensory to subglottic area (6) Arteries Superior laryngeal artery a branch of the superior thyroid, travels with the superior laryngeal nerve Inferior laryngeal artery a branch of the inferior thyroid, travels with the recurrent laryngeal nerve (7) Miscellaneous Information all intrinsic muscles of the larynx are innervated by the recurrent laryngeal of CN X except cricothyroid (superior laryngeal) interarytenoid (transverse arytinoid) connects the posterior aspects of the arytenoid cartilages; adducts vocal cords; only unpaired muscle in the larynx thyro-arytenoid run from posterior surface of the medial aspect of the thyroid cartilage to the anterolateral surfaces of the arytenoid cartilages; pulls the arytenoid cartilages forward to relax the vocal cords vocalis: slips of muscle from the thyroarytenoids go directly to the vocal cords and make fine adjustments oblique arytenoid run from the posterolateral process of one arytenoid to the superior part of the other; fibers continue to the epiglottis as the aryepiglottic mm; result is that contraction both closes the vocal cords, and depresses the epiglottis thus closing the trachea in two ways when swallowing ventricle space between the true and false vocal cords; ends in a blind pouch that contains glands to moisten the cords