The Larynx

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The larynx (LAIR-inks), or "voicebox" (figs. 22.4 and 22.5), is a cartilaginous chamber about 4 cm (1.5 in.) long. Its primary function is to keep food and drink out of the airway, but it has evolved the additional role of producing sound.

The superior opening of the larynx, the glottis,3 is guarded by a flap of tissue called the epiglottis.4 During swallowing, extrinsic muscles of the larynx pull the larynx upward toward the epiglottis, the tongue pushes the epiglottis downward to meet it, and the epiglottis directs food and drink into the esophagus dorsal to the airway. The vestibular folds of the larynx, discussed shortly, play a greater role in keeping food and drink out of the airway, however. People who have had their epiglottis removed because of cancer do not choke any more than when it was present.

In infants, the larynx is relatively high in the throat and the epiglottis touches the soft palate. This creates a more or less continuous airway from the nasal cavity to the larynx and allows an infant to breathe continually while swallowing. The epiglottis deflects milk away from

3glottis = back of the tongue

4epi = above, upon

Trachea Hyoid Bone

Thyroid cartilage Laryngeal prominence

Arytenoid cartilage

Trachea

(a) Anterior

Epiglottis Hyoid bone

Thyroid cartilage Laryngeal prominence

Arytenoid cartilage

Cricoid cartilage

Trachea

Epiglottis Hyoid bone

Cricoid cartilage

Tracheal Anatomy Posterior Aspect

(b) Posterior

Figure 22.4 Anatomy of the Larynx. (a) Anterior aspect. (b) Posterior aspect. (c) Median section, anterior aspect facing left.

Epiglottis-

Hyoid bone-

Epiglottic cartilage

Fat pad

Thyroid cartilage Cuneiform cartilage Corniculate cartilage Vestibular fold

Vocal cord Arytenoid cartilage Arytenoid muscle Cricoid cartilage

Tracheal cartilage

Cartilage The Respiratory System

Midsagittal

(a) Anterior

(b) Posterior

Midsagittal

Figure 22.4 Anatomy of the Larynx. (a) Anterior aspect. (b) Posterior aspect. (c) Median section, anterior aspect facing left.

Saladin: Anatomy & I 22. The Respiratory System I Text I © The McGraw-Hill

Physiology: The Unity of Companies, 2003 Form and Function, Third Edition

846 Part Four Regulation and Maintenance

846 Part Four Regulation and Maintenance

Superior View Larynx
Figure 22.5 Superior View into the Larynx of a Living Person, as Seen with a Laryngoscope.

the airstream, like rain running off a tent while it remains dry inside. By age two, the root of the tongue becomes more muscular and forces the larynx to descend to a lower position.

The framework of the larynx consists of nine cartilages. The first three are relatively large and unpaired. The most superior one, the epiglottic cartilage, is a spoon-shaped supportive plate in the epiglottis. The largest, the thyroid cartilage, is named for its shieldlike shape. It has an anterior peak, the laryngeal prominence, commonly known as the Adam's apple. Testosterone stimulates the growth of this prominence, which is therefore significantly larger in males than in females. Inferior to the thyroid cartilage is a ringlike cricoid5 (CRY-coyd) cartilage, which connects the larynx to the trachea.

The remaining cartilages are smaller and occur in three pairs. Posterior to the thyroid cartilage are the two arytenoid6 (AR-ih-TEE-noyd) cartilages, and attached to their upper ends are a pair of little horns, the corniculate7 (cor-NICK-you-late) cartilages. The arytenoid and cornic-ulate cartilages function in speech, as explained shortly. A pair of cuneiform8 (cue-NEE-ih-form) cartilages support the soft tissues between the arytenoids and the epiglottis. The epiglottic cartilage is elastic cartilage; all the others are hyaline.

The walls of the larynx are also quite muscular. The deep intrinsic muscles operate the vocal cords, and the superficial extrinsic muscles connect the larynx to the hyoid bone and elevate the larynx during swallowing. The extrinsic muscles, also called the infrahyoid group, are named and described in chapter 10.

The interior wall of the larynx has two folds on each side that stretch from the thyroid cartilage in front to the arytenoid cartilages in back. The superior pair, called the

5crico = ring + oid = resembling

6aryten = ladle

Bcune = wedge + form = shape vestibular folds (fig. 22.5), play no role in speech but close the glottis during swallowing. The inferior pair, the vocal cords (vocal folds), produce sound when air passes between them. They are covered with stratified squamous epithelium, best suited to endure vibration and contact between the cords.

The intrinsic muscles control the vocal cords by pulling on the corniculate and arytenoid cartilages, causing the cartilages to pivot. Depending on their direction of rotation, the arytenoid cartilages abduct or adduct the vocal cords (fig. 22.6). Air forced between the adducted vocal cords vibrates them, producing a high-pitched sound when the cords are relatively taut and a lower-pitched sound when they are more relaxed. In adult males, the vocal cords are longer and thicker, vibrate more slowly, and produce lower-pitched sounds than in females. Loudness is determined by the force of the air passing between the vocal cords. The crude sounds of the vocal cords are formed into words by actions of the pharynx, oral cavity, tongue, and lips.

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Responses

  • senait
    What is the primary muscle that deflects the epiglottis?
    6 years ago

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