Larynx
The
larynx (plural
larynges), or
voicebox, is an
organ in the
neck of
mammals involved in protection of the
trachea and sound production. The larynx houses the
vocal cords, and is situated at the point where the upper tract splits into the
trachea and the
esophagus.
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Ligaments of the larynx. Posterior view. |
The structure of the larynx is mainly composed of
cartilage bound by
ligaments and
muscle. At the front is the
thyroid cartilage, creating the prominence of the
Adam's apple in humans. The inferior horns (protrusions at the bottom rear of the thyroid cartilage) of the
thyroid cartilage rest on a ring-shaped cartilage called the
cricoid cartilage which connects the larynx to the trachea. The cricoid cartilage resembles a signet ring (narrow in front, broader in back). Above the larynx is the
hyoid bone, by which (via various muscles and ligaments) the larynx is connected to the jaw and skull. These muscles move the larynx during
swallowing. The
hyoid is the only floating bone in the body; it is not 'attached' to any other bones. The
epiglottis is another cartilage that extents upwards behind the back of the
tongue and projects down through the hyoid bone. It connects to the thyroid cartilage just beneath the thyroid notch (the
Adam's apple).
The space defined by these main cartilages can be divided roughly into the
supraglottis at the top and the
glottis.
The glottis is defined as the space between the vocal folds (more commonly known as vocal cords), which are located at the upper rim of the cricoid cartilage. They attach to the thyroid cartilage at the front, and to the
Arytenoid cartilages at the back. These are two roughly tetrahedral cartilages responsible for pulling the vocal folds together and apart (adduction and abduction â€" see
Anatomical terms of location). The glottis is the laryngeal area of most interest to speech researchers, as it is widely believed to be where most of the control of
phonation and
pitch goes on. The vocal folds are muscular masses coated with a mucous membrane which protects much of the respiratory tract from foreign particles. Their inner edges contain the
vocal ligament.
The supraglottis is that part of the pharynx above the glottis. It contains the ventricle of the larynx (laryngeal sinus), the ventricular folds (or false vocal folds), the
epiglottis, and the
aryepiglottal folds â€" two folds of connective tissue that connect the
epiglottis to the
arytenoid cartilages. Muscles in the
aryepiglottal folds can pull the leaf-shaped
epiglottis down, sealing the larynx and protecting the
trachea below from foreign objects.
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Cricothyroid muscle tensor for vocal ligament
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Posterior cricoarytenoid muscle abductor for vocal ligament
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Lateral cricoarytenoid muscle adductor for vocal ligament
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Oblique Arytenoid muscle closes the larynx orfice
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Transverse Arytenoid muscle adductor for vocal ligament
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epiglottic Arytenoid muscle closes the larynx orfice
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Thyroarytenoid muscle make vocal ligament relaxes
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The entrance to the larynx, viewed from behind. |
During swallowing, the larynx (at the
epiglottis and at the
glottis) closes to prevent swallowed material from entering the
lungs; there is also a strong
cough reflex to protect the lungs. Sensation is transferred by the
superior laryngeal nerve (glottis and supraglottis - Sensory and Autonomic Innervation) and the
recurrent laryngeal nerve (subglottis and muscles - Sensory and Motor Innervation), both branches of the
vagus nerve.
While articulation of the sound (the fine manipulation that creates the many different vowel and consonant sounds of the world's languages) is achieved by the use of the
teeth,
tongue,
palate, and
lips, sound is generated in the larynx, and that is where
pitch and
volume are manipulated.
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, and by manipulating the tension of the muscles within the vocal folds. This causes the pitch produced during
phonation to rise or fall.
In most animals, including infant humans, the larynx is situated very high in the throat â€" a position that allows it to couple more easily with the nasal passages, so that breathing and eating are not done with the same apparatus. However, some
aquatic mammals, large
deer, and adult humans have descended larynges. An adult human cannot raise the larynx enough to directly couple it to the nasal passage.
Some linguists have suggested that the descended larynx, by extending the length of the vocal tract and thereby increasing the variety of sounds humans could produce, was a critical element in the development of
speech and
language. Others cite the presence of descended larynges in non-linguistic animals, as well as the ubiquity of
nonverbal communication and language among humans, as counterevidence against this claim.
There are several things that can cause a larynx to not function properly. Some symptoms are hoarseness, loss of voice, pain in the throat or ears, and breathing difficulties.
Acute laryngitis is the sudden inflammation and swelling of the larynx. It is caused by the common cold or by excessive shouting. It is not serious.
Chronic laryngitis is caused by smoking, dust, frequent yelling, or prolonged exposure to polluted air. It is much more serious than acute laryngitis.
Presbylarynx is a condition in which age-related atrophy of the soft tissues of the larynx results in weak voice and restricted vocal range and stamina. Bowing of the anterior portion of the vocal cords is found on laryngoscopy.
Ulcers may be caused by the prolonged presence of an
endotracheal tube.
Polyps and
nodules are small bumps on the
vocal cords caused by prolonged exposure to
cigarette smoke and vocal overuse, respectively. Finally, two related types of
cancer of the larynx, namely
squamous cell carcinoma and
verrucous carcinoma, are strongly associated with repeated exposure to cigarette smoke and alcohol.
Vocal cord paresis is weakness of one or both vocal folds that can greatly impact daily life. Symptoms of paresis include: hoarseness, vocal fatigue, pain in the throat when speaking, shortness of breath, and aspiration (food or liquids going down the trachea).
Some of the primary causes of paresis include: viral infection, cancer or tumor compressing the recurrent laryngeal nerve, trauma, compression of the vocal cord nerve from intubation, or laryngopharyngeal reflux. Many patients may also experience paresis from an unknown cause (idiopathic).
Paresis can be diagnosed by a lack of motion of one or both cords on laryngoscopy, and more precisely by EMG (electromyography) which measures the level of electrical activity in the muscles of the larynx. This diagnosis can be made by a laryngologist, or by some otolaryngologists. In some cases, the nerves may heal and full motion of the vocal cords may return. In other cases, surgery may be required to provide temporary or permanent medialization of the vocal cords.
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Laryngitis*
EpiglottitisSpeech and Hearing Science: Anatomy and Physiology 3rd edition. Willard R. Zemlin. 1988. Prentice-Hall, Inc. Englewood Cliffs, New Jersey. ISBN 0-13-827429-0
