The strength of expiration from the lungs also contributes to loudness. Manipulation of the larynx is used to generate a source sound with a particular fundamental frequency, or pitch. This source sound is altered as it travels through the vocal tract, configured differently based on the position of the tongue, lips, mouth, and pharynx. The process of altering a source sound as it passes through the filter of the vocal tract creates the many different vowel and consonant sounds of the worlds languages as well as tone, certain realizations of stress and other types of linguistic prosody. The larynx also has a similar function to the lungs in creating pressure differences required for sound production; a constricted larynx can be raised or lowered affecting the volume of the oral cavity as necessary in glottalic consonants. The vocal cords can be held close together (by adducting the arytenoid cartilages) so that they vibrate (see phonation). The muscles attached to the arytenoid cartilages control the degree of opening. Vocal cord length and tension can be controlled by rocking the thyroid cartilage forward and backward on the cricoid cartilage (either directly by contracting the cricothyroids or indirectly by changing the vertical position of the larynx), by manipulating the tension of the muscles within the vocal cords, and by moving the arytenoids forward or backward. This causes the pitch produced during phonation to rise or fall. In most males the vocal cords are longer and have a greater mass than most females vocal cords, producing a lower pitch.
Injury to the external branch of the superior laryngeal nerve causes weakened phonation because the vocal cords cannot be tightened. Injury to one of the recurrent laryngeal nerves produces hoarseness, if both are damaged the voice may or may not be preserved, but breathing becomes difficult. Development
In newborn infants, the larynx is initially at the level of the C2–C3 vertebrae, and is further forward and higher relative to its position in the adult body. The larynx descends as the child grows. Laryngeal cavity
The laryngeal cavity (cavity of the larynx) extends from the laryngeal inlet downwards to the lower border of the cricoid cartilage where it is continuous with that of the trachea.It is divided into two parts by the projection of the vocal folds, between which is a narrow triangular opening, the rima glottidis. The portion of the cavity of the larynx above the vocal folds is called the laryngeal vestibule; it is wide and triangular in shape, its base or anterior wall presenting, however, about its center the backward projection of the tubercle of the epiglottis. It contains the vestibular folds, and between these and the vocal folds are the laryngeal ventricles. The portion below the vocal folds is called the infraglottic cavity. It is at first of an elliptical form, but lower down it widens out, assumes a circular form, and is continuous with the tube of the trachea. Function
Sound generation
Sound is generated in the larynx, and that is where pitch and volume are manipulated.