Larynx
The larynx, which lies at the level of the third through sixth
cervical vertebrae, serves as the organ of phonation and as a valve to protect the
lower airways from the contents of the alimentary tract. The structure consists
of muscles, ligaments, and a framework of cartilages. These include the thyroid,
cricoid, arytenoids, corniculates, and the epiglottis. The epiglottis, a fibrous
cartilage, has a mucous membrane covering that reflects as the glossoepiglottic fold
onto the pharyngeal surface of the tongue. On either side of this fold are depressions
called valleculae. These areas provide the site for placement of the curved MacIntosh
laryngoscope blade. The epiglottis projects into the pharynx and overhangs the laryngeal
inlet. However, it is not absolutely essential for sealing off the airway during
swallowing.
The laryngeal cavity extends from the epiglottis to the lower
level of the cricoid cartilage. The inlet is formed by the epiglottis, which joins
to the apex of the arytenoid cartilages on each side by the aryepiglottic folds.
Inside the laryngeal cavity are the vestibular folds, which are narrow bands of
fibrous tissue on each side. These extend from the anterolateral surface of each
arytenoid to the angle of the thyroid, where the latter attaches to the epiglottis.
These folds are referred to as the false vocal cords and are separated from the
true vocal cords by the laryngeal sinus or ventricle. The true vocal cords are pale,
white, ligamentous structures that attach to the angles of the thyroid anteriorly
and to the arytenoids posteriorly. The triangular fissure between these vocal cords
is the glottic opening, which represents the narrowest segment of the laryngeal opening
in adults. In children younger than 10 years, the narrowest segment lies just below
the cords at the level of the cricoid ring. The mean length of the relaxed open
glottis is about 23 mm in males and 17 mm in females. The glottic width is 6 to
9 mm but can be stretched to 12 mm. The cross-sectional area of the relaxed glottis
may be 60 to 100 mm2
.
The scope of this chapter does not permit a detailed description
of the actions of the laryngeal muscles; however, these muscles may be classified
into three basic groups relative to their actions on the cords: abductors, adductors,
and regulators of tension. The entire motor innervation to these muscles and the
sensory supply to the larynx are supplied by two branches of the vagus nerve: the
superior and recurrent laryngeal nerves. This motor and sensory innervation is summarized
in Table 42-1
.
