Muscle control and some of the forces involved in speech breathing and voice Forces muscle contraction shorten the muscle muscle elasticity return to resting length lung elasticity return to resting volume aerodynamic suction the Bernouli force aerodynamic pressure In inhaling the rib cage is expanded by pulling the ribs up In exhaling the rib cage is deflated by pulling the ribs down This is done by the external intercostal muscles This is done by the internal intercostal muscles External intercostal mucles lifting the rib cage expanding the thoractic cavity Internal intercostal mucles drawing down the rib cage shrinking the thoractic cavity Electrical activity of the internal and external intercostal muscles during a string of syllables Draper Ladefoged Whitteridge 1960 External intercostals Speech envelope Lung volume Internal intercostals time sec Early during exhale the main muscle activity is of the inhaling muscles opposing the elastic recoil of muscles and lung tissue Lung tissue elasticity imagine blowing up a balloon by pulling on the handle The elastic surface of the balloon will tend to contract as soon as you stop pulling on the handle Here we see a similar pattern activity recorded from surface electrodes on the abdomen exhaling muscles Electrode placements UL upper lateral LL lower lateral UM upper middle MM mid middle LM lower middle Hoit Plassman Lansing and Hixon 1988 Abdominal muscle activity during speech production Journal of Applied Physiology 65 2656 64 The arytenoid cartilages are shaped like pyramids and sit on the upper back edge of the cricoid cartilage They rotate and slide to adduct or abduct the vocal folds View of the larynx from the top View of the larynx from the back To adduct the vocal folds for voicing or glottal stop lateral cricoarytenoids inter arytenoids oblique and transverse To abduct the vocal folds for breathing or voiceless sounds posterior cricoarytenoids oblique transverse arytenoid cartilage posterior cricoarytenoid lateral cricoarytenoid The length of the vocal folds is altered by changing the angle between the thyroid cartilage and the cricoid cartilage When the thyroid is tilted forward the vocal folds are longer and thus thinner and vibrate at a higher rate thus the voice is higher pitched When the thyroid is tilted back the vocal folds are shorter and thus thicker and vibrate at a lower rate thus the voice is lower pitched Therefore the main muscle in the larynx that controls pitch for tone and intonation in language and for carrying a tune in singing is the cricothyroid arytenoid cartilage cricothyroid Voicing phonation the vocal folds slap together producing noise This is a myoelastic aerodynamic process Air pressure below the glottis forces the vocal folds open 1 2 3 Muscle elasticity and the Bernoulli force close the vocal folds 4 5 6 The Bernoulli force in phonation High velocity through narrow passage negative pressure perpendicular to direction of flow Fas Fb Ft ma Fas aerostatic force pressure on the surface of the vocal folds Fb Bernoulli force Ft tissue force muscle elasticity m mass of the vocal folds a acceleration of the vocal folds
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