Function of a Larynx

Sound generation

Sound is generated in the larynx, and that is where pitch and volume are manipulated. 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 world's 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 folds 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 fold 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 folds, and by moving the arytenoids forward or backward. This causes the pitch produced during phonation to rise or fall. In most males the vocal folds are longer and with a greater mass than most females' vocal folds, producing a lower pitch.

The vocal apparatus consists of two pairs of mucosal folds. These folds are false vocal folds (vestibular folds) and true vocal folds (folds). The false vocal folds are covered by respiratory epithelium, while the true vocal folds are covered by stratified squamous epithelium. The false vocal folds are not responsible for sound production, but rather for resonance. The exceptions to this are found in Tibetan Chant and Kargyraa, a style of Tuvan throat singing. Both make use of the false vocal folds to create an undertone. These false vocal folds do not contain muscle, while the true vocal folds do have skeletal muscle.

Other[edit]

The most important role of the larynx is its protecting function; the prevention of foreign objects from entering the lungs by coughing and other reflexive actions. A cough is initiated by a deep inhalation through the vocal folds, followed by the elevation of the larynx and the tight adduction (closing) of the vocal folds. The forced expiration that follows, assisted by tissue recoil and the muscles of expiration, blows the vocal folds apart, and the high pressure expels the irritating object out of the throat. Throat clearing is less violent than coughing, but is a similar increased respiratory effort countered by the tightening of the laryngeal musculature. Both coughing and throat clearing are predictable and necessary actions because they clear the respiratory passageway, but both place the vocal folds under significant strain.^[8]

Another important role of the larynx is abdominal fixation, a kind of Valsalva maneuver in which the lungs are filled with air in order to stiffen the thorax so that forces applied for lifting can be translated down to the legs. This is achieved by a deep inhalation followed by the adduction of the vocal folds. Grunting while lifting heavy objects is the result of some air escaping through the adducted vocal folds ready for phonation.^[8]

Abduction of the vocal folds is important during physical exertion. The vocal folds are separated by about 8 mm (0.31 in) during normal respiration, but this width is doubled during forced respiration.^[8]

During swallowing, elevation of the posterior portion of the tongue levers (inverts) the epiglottis over the glottis' opening to prevent swallowed material from entering the larynx which leads to the lungs, and provides a path for a food or liquid bolus to "slide" into the esophagus; the hyo-laryngeal complex is also pulled upwards to assist this process. Stimulation of the larynx by aspirated food or liquid produces a strong cough reflex to protect the lungs.

In addition, intrinsic laryngeal muscles are spared from some muscle wasting disorders, such as Duchenne muscular dystrophy, may facilitate the development of novel strategies for the prevention and treatment of muscle wasting in a variety of clinical scenarios. ILM have a calcium regulation system profile suggestive of a better ability to handle calcium changes in comparison to other muscles, and this may provide a mechanistic insight for their unique pathophysiological properties

The larynx is composed of an external skeleton of cartilage plates that prevents collapse of the structure. The plates are fastened together by membranes and muscle fibres. The front set of plates, called thyroid cartilage, has a central ridge and elevation commonly known as the Adam’s apple. The plates tend to be replaced by bone cells beginning from about 20 years of age onward.

The epiglottis, at the upper part of the larynx, is a flaplike projection into the throat. As food is swallowed, the whole larynx structure rises to the epiglottis so that the passageway to the respiratory tract is blocked. After the food passes into the esophagus (food tube), the larynx relaxes and resumes its natural position.

The centre portion of the larynx is reduced to slitlike openings in two sites. Both sites represent large folds in the mucous membrane lining the larynx. The first pair is known as the false vocal cords, while the second is the true vocal cords (glottis). Muscles attached directly and indirectly to the vocal cords permit the opening and closing of the folds. Speech is normally produced when air expelled from the lungs moves up the trachea and strikes the underside of the vocal cords, setting up vibrations as it passes through them; raw sound emerges from the larynx and passes to the upper cavities, which act as resonating chambers (or in some languages, such as Arabic, as shapers of sound), and then passes through the mouth for articulation by the tongue, teeth, hard and soft palates, and lips. If the larynx is removed, the esophagus can function as the source for sound, but the control of pitch and volume is lacking.

larynx IS ALSO CALLED VOICE BOX