741
CHAPTER NINETEEN
Respiratory System
During normal breathing the vocal cords remain relaxed,
and the opening between them, called the
glottis
(glot
is), is
a triangular slit. However, when food or liquid is swallowed,
muscles close the glottis in the false vocal folds. Along with
closing of the epiglottis, this action helps prevent food or liq-
uid from entering the trachea
(f g. 19.7)
. The mucous mem-
brane that lines the larynx continues to F lter incoming air by
entrapping particles and moving them toward the pharynx
by ciliary action.
PRACTICE
7
What part of the respiratory tract is shared with the alimentary
canal?
8
Describe the structure of the larynx.
9
How do the vocal cords produce sounds?
10
What is the function of the epiglottis? Of the glottis?
vocal cords during speech and aid in closing the larynx dur-
ing swallowing.
The
cuneiform cartilages
are small, cylindrical struc-
tures in the mucous membrane between the epiglottic and the
arytenoid cartilages. They stiffen the soft tissues in this region.
Inside the larynx, two pairs of horizontal folds com-
posed of muscle tissue and connective tissue with a covering
of mucous membrane extend inward from the lateral walls.
The upper folds (vestibular folds) are called
false vocal cords
because they do not produce sounds. Muscle F
bers within
these folds help close the larynx during swallowing.
The lower folds are the
true vocal cords.
They have elastic
F bers and are responsible for vocal sounds, which are created
when air is forced between these folds, vibrating them. This
action generates sound waves, formed into words by chang-
ing the shapes of the pharynx and oral cavity and by using the
tongue and lips.
Figure 19.6
shows both pairs of cords.
Changing tension on the vocal cords, by contracting or
relaxing laryngeal muscles, controls
pitch
(musical tone) of
the voice. Increasing the tension produces a higher pitch,
and decreasing the tension creates a lower pitch.
The
intensity
(loudness) of a vocal sound depends upon
the force of the air passing over the vocal cords. Stronger
blasts of air result in greater vibration of the vocal cords and
louder sound.
FIGURE 19.5
Larynx. (
a
) Anterior and (
b
) posterior views of the larynx.
T
Epiglottic cartilage
Hyoid bone
Thyroid cartilage
Cricoid cartilage
Hyoid bone
Epiglottic cartilage
Thyroid cartilage
Cricoid cartilage
(b)
rachea
Trachea
(a)
False vocal cord
Glottis
True vocal
cord
Epiglottis
Hyoid bone
Thyroid cartilage
Cricoid cartilage
Hyoid bone
Epiglottis
False vocal
cord
Thyroid cartilage
Cricoid cartilage
Thyroid
cartilage
Corniculate
cartilage
Cuneiform
cartilage
Arytenoid
cartilage
True vocal
cord
(b)
(a)
FIGURE 19.6
±Larynx.±(
a
) Frontal section and (
b
) sagittal section of
the larynx.
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