The vocal folds must be closed and the ratio of air pressure below the glottis (subglottal) to air pressure above the glottis (supraglottal) must exceed a certain positive value for phonation to occur. In other words, subglottal pressure (Psg) must exceed supraglottal pressure by a certain amount for phonation to occur.
In modal phonation the cartilaginous glottis must be closed to prevent leakage of air typical of breathy voice. The vocal folds are adducted (held together) and a certain amount of tension is applied to the vocal folds. Extremes of length, thickness and tension can result in creaky voice (short, thick, low tension vocal folds) or falsetto voice (elongated, thin, high tension vocal folds).
Forces of exhalation cause a build up in air pressure below the closed glottis. Phonation occurs when Psg reaches a certain value (dependent upon vocal fold tension). The air pressure forces the vocal folds apart when the force of the air pressure exceeds the elastic forces holding them closed. This causes Psg to drop as air escapes from below the glottis. When Psg drops to a certain level, elastic and aerodynamic forces cause the vocal folds to snap shut again. Psg then builds up again and the cycle is repeated. This pattern is repeated to create a periodic series of glottal opening and closing patterns. During phonation each cycle can be characterised by a closed and an open phase.
The vocal folds must be closed and the ratio of air pressure below the glottis (subglottal) to air pressure above the glottis (supraglottal) must exceed a certain positive value for phonation to occur. In other words, subglottal pressure (Psg) must exceed supraglottal pressure by a certain amount for phonation to occur.In modal phonation the cartilaginous glottis must be closed to prevent leakage of air typical of breathy voice. The vocal folds are adducted (held together) and a certain amount of tension is applied to the vocal folds. Extremes of length, thickness and tension can result in creaky voice (short, thick, low tension vocal folds) or falsetto voice (elongated, thin, high tension vocal folds).Forces of exhalation cause a build up in air pressure below the closed glottis. Phonation occurs when Psg reaches a certain value (dependent upon vocal fold tension). The air pressure forces the vocal folds apart when the force of the air pressure exceeds the elastic forces holding them closed. This causes Psg to drop as air escapes from below the glottis. When Psg drops to a certain level, elastic and aerodynamic forces cause the vocal folds to snap shut again. Psg then builds up again and the cycle is repeated. This pattern is repeated to create a periodic series of glottal opening and closing patterns. During phonation each cycle can be characterised by a closed and an open phase.
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