Physiology of Speech
*The production of speech is a highly complex motor task that involves approximately 100 orofacial, laryngeal, pharyngeal, and respiratory muscles.
* Speech can be defined as waves of air pressure created by airflow pressed out of the lungs and going out through the mouth and nasal cavities. The air passes through the vocal folds (chords) via the path from the lungs through the vocal tract, vibrating them at different frequencies.
*Speech production requires airflow from the lungs (respiration) to be phonated through the vocal folds of the larynx (phonation) and resonated in the vocal cavities shaped by the jaw, soft palate, lips, tongue and other articulators (articulation)such as : The Vocal tract, The Pharynx, The Glottis, The Velum, The Teeth, The Nose and Larynx.
The Articulators
The structures involved in the articulation of speech can be classified into two categories:
• Movable : Lips, Tongue, Soft Palate, Pharynx, Mandible
• Fixed : Incisors, Hard Palate, Aleolar Ridge
Mechanism
Speech sound is a wave of air that originates from complex actions of the human body, supported by three functional units:
- Generation of air pressure
- Regulation of vibration
- Control of resonators
The lung air pressure for speech results from functions of the respiratory system during a prolonged phase of expiration after a short inhalation.
Vibrations of air for voiced sounds are introduced by the vocal folds in the larynx; they are controlled by a set of laryngeal muscles and airflow from the lungs. The oscillation of the vocal folds converts the expiratory air into intermittent airflow pulses that result in a buzzing sound.
The narrow constrictions of the airway along the tract above the larynx also generate transient source sounds; their pressure gives rise to an airstream with turbulence or burst sounds. The resonators are formed in the upper respiratory tract by the pharyngeal, oral, and nasal cavities. These cavities act as resonance chambers to transform the laryngeal buzz or turbulence sounds into the sounds with special linguistic functions. The main articulators are the tongue, lower jaw, lips, and velum. They generate patterned movements to alter the resonance characteristics of the supra-laryngeal airway.
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