 Hello and welcome to my e-lecture on phonation. Central to the production of speech is the larynx. It controls and modifies the pulmotic airstream. It produces additional types of airstream, and depending on the state of the glottis, it generates phonation. So these aspects constitute the focus of our e-lecture, where we will first look at the structure and the function of the larynx. Then we will see how we can model the central aspects of phonation. And last but not least, we will look at the role of the larynx in speech. Let us look at the structure of the larynx first. The larynx consists of a number of cartilages which are interconnected by complex joints. And move about these joints by means of muscular and ligamental force. Let us study the anatomical details from various angles. Seen from the front, as you can see over here, the most prominent piece of the larynx is the thyroid cartilage. Part of it forms Adam's apple, which you can see even from the outside. The horseshoe-shaped hyoid bone, here at the top, lies on top of the larynx, elevating the larynx during swallowing and speech. Additionally, we can see the epiglottis over here on top. And of course, the trachea down here, with the cricoid cartilage on top. If we turn around the larynx and use the rear view, we can additionally see the arytenoids, the cartilages to which the vocal folds are attached. The sagatal view nicely exhibits the position of the arytenoid cartilages, which you can see here on the left, and part of the vocal folds or vocal cords over here. The vocal folds are attached at the front to the thyroid cartilage and at the back to the arytenoids. And in the top view, we can see that in the center of the larynx lie the vocal folds here or vocal cords and the space between the vocal cords or vocal folds is called the glottis. For normal breathing, the vocal folds are spaced well apart and they come together when sound is produced. And sometimes the vocal folds may be closed, blocking the flow of air and then open suddenly to produce a glottal stop as in a-a or to use an example from Cockney English but-a instead of but-a. The larynx has several functions. The primary biological function of the larynx is a protective function where the larynx acts as a valve by closing off air from the lungs or preventing foreign substances from entering the trachea. The principal example of this protective function of the larynx is the glottal closure during which the laryngeal muscles close the airway while swallowing. A second function is the respiratory function. During respiration, the larynx controls the airflow from subglottal to supraglottal regions. And the larynx is a gateway to the airway and thus in order for air to go into the respiratory system, the larynx must be wide open. During inhalation, the vocal cords abduct away from the midline resulting in a widening of the chink. And during exhalation, there is a relative adduction of the vocal cords and a narrowing of the chink. Moreover, the entire larynx is displaced down in inspiration and up in expiration. The third function of course is the linguistic function in speech where the larynx modifies the airflow from the lungs in such a way as to produce an acoustic signal. The result is phonation. Phonatory vibration of the vocal cords involves first the arrest of rhythmic respiration, then the adduction of the arytenoids with or without repositioning of the larynx and the initiation of voluntary expiration. Length and tension of the vocal cords during this process are slightly increased as you can see over here. And the laryngeal passage becomes occluded at the level of the glottis. The whole mechanism of vocal fold vibration can best be explained by means of an aerodynamic model. Let us look at this model of phonation in more detail. It involves three steps. Step one, adduction and opposition of the arytenoid cartilages in the midline and the immobilization of the posterior ends of the vocal ligaments. Second step, elongation and increased tension in the vocal ligaments. And step three, airflow through the glottis supplying the energy for vibration. The most widely accepted model to describe vocal fold vibration is referred to as the aerodynamic myoelastic model of phonation. It refers to the air pressure and airflow facts, the aerodynamic component, as well as to the mechanical factors involved in muscular activity, the myoelastic component. In short, it can be described like this. The aerodynamic factor involved in the theory of phonation is called the Bernoulli effect, named after Daniel Bernoulli, a Swiss mathematician and physicist. The most practical example of this is in the action of an airfoil. The shape of an airplane wing is such that the air flowing over the top of the wing must travel faster than the air flowing under the wing. And so there is less pressure on top than on the bottom resulting in a lift. We can also demonstrate this with a piece of paper. So here I have a piece of paper. If I now blow air over the top of this piece of paper, the air moves fast along the top and the paper will move up, just like the plane to which a wing is attached. Vocal fold oscillation is similar. The pulmonic air stream causes the vocal folds to be sucked together, creating a closed airspace below the glottis. Down here. Continued air pressure from the lungs builds up underneath the closed folds. And once this air pressure becomes high enough, the folds are blown outward, thus opening the glottis and releasing a single puff of air. And now the muscular or myoelastic effect comes in. The lateral movement of the vocal folds continues until the natural elasticity of the tissue takes over. And the vocal folds move back to their original closed position. Then the cycle begins again, similar to the vibration of a rubber band when I blow air through it. Now here I have a rubber band. In summary, two factors control glottal opening and closure. The aerodynamics of the airflow, opening the glottis via an air stream, and the elastic tension in the laryngeal muscles that is working to close the glottis. Each cycle produces a single puff of air. The sound of the human voice is thus nothing more than tens or hundreds of these small puffs of air being released every second and filtered by the vocal tract. Depending on the tension and elongation of the vocal folds, various types of phonation are possible. The default is nil phonation or voicelessness. It requires a more or less wide opening of the glottis resulting in glottal silence. A normal voice or just voice refers to normal vocal cord vibration occurring along most of the length of the glottis. Whisper, this is an example of whisper, requires a far greater constriction than the voiceless setting of the glottis and is generally achieved by adducting the vocal cords while maintaining an opening between the arytenoids. In breathy voice, this is an example of breathy voice. Normal cord vibration is accompanied by some continuous turbulent airflow. Creaky voice, and here you have an example of creaky voice. Creaky voice is a phonation mode characterised by a low frequency of vibration of the vocal cords. And finally falsetto, falsetto is the phonation mode and this would be an example where the vocal cords are stretched longitudinally so that they become relatively thin in cross-section. Thus falsetto is primarily heard as a phonatory setting in singing. Do you remember the famous BG songs, Saturday night fever, night fever? Just listen and you know what falsetto is. Apart from phonation, the larynx is also involved in the production of a particular airstream, the so-called glottalic airstream and this airstream involves the closure of the glottis, a so-called glottal closure. At the same time, a closure is produced somewhere in the vocal tract. There are two variants of this airstream. If the larynx is moved upward during these two closures and the oral closure is released, the result is a so-called ejective consonant, such as up-ah or ak-ah. See my larynx moving upwards, ak-ah. The second variant is referred to as glottalic ingressive. So if by contrast the larynx is lowered and the oral closure is released, the result is an implosive sound, such as um-bah or ag-ah. See my larynx moving downwards, ag-ah. Well, so much for the larynx. Its structure, its general function and its contribution to speech. You should now understand how the larynx is involved in speech production and, in particular, you should be familiar with the aerodynamic myoelastic model of phonation. That's it for now. Thanks for your attention.