Conclusion - Tissue Functioning and Remodeling in the Circulatory and Ventilatory Systems - page 801

Table 14.1. Respiratory centers of the central nervous system.

Brain region Respiratory centers Function

Pons Pneumotaxic center Inhibition of inspiratory center

(limitation of inspiration duration)

Apneustic center Inspiration activation

Medulla oblongata Inspiratory center Inspiration

Activation of diaphragm
and external intercostal muscles

Expiratory center Deep and/or forced expiration

Activation of abdominal muscles
and internal intercostal muscles

results from the relaxation of the diaphragm and intercostal muscles and lung elastic
recoil. A feedback control is ensured by central and peripheral chemoreceptors and
mechanoreceptors.
When breathing increases, such as during exercise and coughing that helps to
remove large foreign bodies from the respiratory tract as well as smaller particles
entrapped in the mucus coating the respiratory epithelium, the expiratory center
primes the contraction of abdominal muscles and 11 internal intercostals (or
intercostales interni). 2 The expiratory center (ventral group of respiratory neurons)
formed by neurons of the nuclei ambiguus and retro-ambiguus is located anteriorly
and laterally with respect to the inspiratory center.
The nervous centers change the amplitude and rhythm of respiration upon
reception of feedback signals sent by sensory neurons. The Hering-Breuer reflex
that uses the vagus nerve prevents lung overinflation (Table 14.2 ). When lung
airways expand during inhalation, the vagus nerve conveys information to the
medulla oblongata that, in response, temporarily inhibits the inspiratory center,
thereby priming expiration. Once bronchi and bronchioles return to resting size, the
vagus nerve ceases to send inhibitory signals, and the inspiratory center reinitiates
inspiration.
The pneumotaxic center (or pontine respiratory group) located in the pons
provides cyclic inhibitory impulses to the inspiratory center, thereby decreasing the
tidal volume. This center, which controls the breathing amplitude and respiratory
frequency, is only active during elevated breathing. The apneustic center, also
situated in the pons, activates inspiration at rest. The apneustic center activity
is canceled out by the pneumotaxic center when the breathing rate increases.
Conversely, the apneustic center delays arrest signals from the pneumotaxic center.

2 External intercostals (or intercostales externi) work in unison during deep inspiration. These
thick muscles are directed obliquely downward and laterally. Internal intercostals are also directed
obliquely, but in a direction opposite to that of external intercostals. Internal intercostal muscles
counteract the action of external intercostal muscles.