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larynx


larynx
Larynx. Cross-sectional diagram
Known commonly as the voice box or "Adam's apple," an organ in the neck of humans and other mammals that is involved in the production of sound and also serves to protect the upper part of the trachea (windpipe). The larynx houses the vocal folds (vocal chords) and is shaped like a funnel, with walls of cartilage and a highly complicated system of muscles. It lies just below where the tract of the pharynx splits into the trachea and the esophagus, extending from the fourth to the sixth vertebral levels.

The larynx is often divided into three sections: sublarynx, larynx, and supralarynx. It is formed by nine cartilages – the epiglottis, thyroid, cricoid, arytenoid (two), corniculate (two), and cuneiform (two) – that are connected to each other by muscles and ligaments and lined with mucous membrane. Movement of these cartilages alters the tension of the vocal folds, which changes the pitch of the sound emitted by the vocal folds when they vibrate.


Functions of the larynx

The most important function of the larynx is to prevent choking. When a person is not eating or drinking, the epiglottis remains upright, keeping the larynx open as part of the airway to the lungs. As soon as swallowing begins, the epiglottis descends like a lid over the larynx, directing food to either side. Closure of the vocal folds also helps protect the airway. The food or drink then passes down the esophagus to the stomach.

The secondary function of the larynx is voice production.


How the larynx produces sounds

larynx cross-section
a) epiglottis; b) aperture of the glottis; c) arytenoid muscles; d) trachea
The opening of the larynx, i.e., the space between the vocal folds is called the glottis. When at rest, and with normal breathing, it is a triangular orifice through which air passes freely. When a sound is to be made, the arytenoid muscles (see artwork) act so as to twist the arytenoid cartilages, and these stretch or slacken the vocal folds, which can assume about 170 different positions. At the same time, the glottis itself is narrowed to a slit, the size of which regulates the rate at which air passes through the larynx from the lungs. The accurately controlled current of air makes the vocal folds vibrate, and so sounds are produced. As produced by the vocal folds these sounds would be too weak and faint to be heard, but the hollows of the respiratory system, in the trachea, the pharynx, the larynx itself, and the nose and mouth, act as resonators which strengthen and modify the sound. The chest also acts as a resonator and amplifies the sound just as the body of a violin does.


How the larynx helps produce words

In the case of humans, the sounds of the voice can be shaped to form words, which are made up of vowels and consonants. The shaping is done by the muscles of the mouth, palate, lips, and tongue. Vowels are accompanied by vibration of the larynx and the sound passes unobstructed through the mouth. Consonants are formed mainly by the alteration of the laryngeal sound by the tongue, teeth, lips, and palate. A word cannot be made up of consonants alone, because most of these cannot be voiced unless a vowel precedes or follows them. Some consonants are called labials (Latin labia, lip) because they are formed by the lips; it is impossible to say b, p, f, m, or v with your mouth alone. Others (d, t, l, n, r, s, z, ch, j) are linguals, requiring the use of the tongue (Latin lingua, tongue). G, q, and k are gutterals, made with the back of the palate (Latin gutter, throat).

The pitch of the voice depends on the frequency of vibrations of the vocal folds. If they are at normal tension the vibrations are about 80 per second; if the cords are tightly stretched they are more rapid, up to 1,000 per second.


Related entry

human skeleton human skeleton


Related categories

   • ANATOMY AND PHYSIOLOGY
   • ACOUSTICS AND MUSIC


Sources: National Cancer Institute; Knowledge magazine p. 304


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