755
CHAPTER NINETEEN
Respiratory System
Internal (expiratory)
intercostal muscles
External (inspiratory)
intercostal muscles
Diaphragm
Fourth
ventricle
Medullary
respiratory
center
Ventral respiratory group
Medulla oblongata
Pons
Pontine respiratory
group
Midbrain
Dorsal respiratory group
Yawning
is familiar to everyone, yet its significance
and the mechanism by which yawning is contagious remain
poorly understood. Evidence points away from a role in
increasing oxygen intake. Yawning, and its effect of getting
others yawning, may be rooted in primitive brainstem mech-
anisms that maintain alertness.
Table 19.5
summarizes the characteristics of nonrespi-
ratory air movements. Clinical Application 19.3 discusses
respiratory problems that affect ventilation.
PRACTICE
27
How is the minute ventilation calculated? The alveolar ventilation
rate?
28
Which nonrespiratory air movements help clear the air passages?
29
Which nonrespiratory air movements are used to express
emotions?
30
What seems to be the function of a yawn?
19.5
CONTROL OF BREATHING
Normal breathing is a rhythmic, involuntary act that con-
tinues when a person is unconscious. However, the respira-
tory muscles can be voluntarily controlled too (Take a deep
breath and consider this!).
Respiratory Areas
Groups of neurons in the brainstem comprise the
respira-
tory areas,
which control breathing. These areas periodically
initiate impulses that travel on cranial and spinal nerves to
breathing muscles, causing inspiration and expiration. The
respiratory areas also adjust the rate and depth of breath-
ing to meet cellular requirements for supply of oxygen and
removal of CO
2
, even during strenuous physical exercise.
The components of the respiratory areas are widely scat-
tered throughout the pons and medulla oblongata. However,
two parts of the respiratory areas are of special interest. They
are the respiratory center of the medulla and the respiratory
group of the pons
(f
g. 19.28)
.
TABLE
19.5
|
Nonrespiratory Air Movements
Air Movement
Mechanism
Function
Coughing
Deep breath is taken, glottis is closed, and air is forced against the closure; suddenly the
glottis is opened, and a blast of air passes upward
Clears lower respiratory passages
Sneezing
Same as coughing, except air moving upward is directed into the nasal cavity by
depressing the uvula
Clears upper respiratory passages
Laughing
Deep breath is released in a series of short expirations
Expresses happiness
Crying
Same as laughing
Expresses sadness
Hiccuping
Diaphragm contracts spasmodically while glottis is closed
No useful function known
Yawning
Deep breath is taken
Some hypotheses, but no established function
Speech
Air is forced through the larynx, causing vocal cords to vibrate; actions of lips, tongue,
and soft palate form words
Vocal communication
FIGURE 19.28
The respiratory areas are located in the pons and the
medulla oblongata.
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