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Larynx, also called voice BOX, a hollow, tubular structure connected to the top of the windpipe (trachea); air passes through the larynx on its way to the lungs. The larynx is also responsible for the sounds produced in talking and singing and prevents the passage of food and other foreign particles into the lower respiratory tracts, The larynx is approximately five centimetres (about two inches) in length in a man and a bit smaller in a woman. The greater size in the male reflects increased growth after puberty because of male reproductive hormones.
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, have 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. Inside the epiglottal flap there is an elastic cartilage that gives support. The top epiglottal surface is covered by a moist mucous membrane. The cells are flat and closely packed together to give this covering resistance to abrasion and irritation by passing food, There are a few taste buds on the surface. The lower side of the epiglottis is covered by a mucous membrane with large column-shaped cells that generally have hairlike projections called cilia. The cilia bend toward the throat to push any particles or mucus away from the respiratory tract.
The centre portion of the larynx is reduced to slitlike openings in two sites. Both sites repre
sentlarge folds in the mucous membrane. The first pair is known as the false vocal cords, while the second is the true vocal cords (glottis) of the larynx. The vocal cords leave a small opening when they are close together and a larger triangular-shaped one when they are apart.
The vocal cords are formed by a ligament, elastic fibres, and the mucous membrane. Muscles attached directly and indirectly to the vocal cords permit the opening and closing of the folds.
Speech is caused by pushing of air from the lungs; the vibrations are created when air passes over the vocal cords; and the articulation of the sounds is formed by the throat, mouth, and nose. The larynx is the fundamentat tone-producing instrument that supplies only the raw sound. The sound passes to the upper cavities, which act as resonating chambers; it then passes over the tongue and lips for word formation. If the larynx is removed, the esophagus can function as the source for sound, but the control of pitch and volume is lacking.
Coughing and sneezing are respiratory reflexes. First the glottis is closed and then suddenly reopened, permitting a burst of air to be forced through the mouth and nose. A hiccup is caused by short, fast inspirations of air through a partially or fully closed glottis; the reflex is precipitated by sudden contractions of the muscular diaphragm under the lungs. Laughter is produced by short jerky exhalations of air accompanied usually by some phonation.
In other forms of animal life, sounds can be produced by the glottis, but word formation is lacking. Reptiles can produce a hissing sound by rushing air through the glottis, which is at the back of the mouth. Frogs when frightened or attracting a mate produce their croaking sounds by passing air back and forth over the vocal folds; a pair of vocal sacs near the mouth serve as resonating chambers. In birds the larynx is a small structure in front of the trachea; it serves only to guard the air passage. Sound is produced in a special organ called the syrinx (q.v.), which is located at the lower end of the trachea. The syrinx is an enlarged area with a pair of membranes that move to alter the pitch of sound. The muscles attached to the membranes determine the complexity of the sounds produced.
