Timing, Sleep, and Respiration in Health and Disease - Progress in Molecular Biology and Translational Science - page 194

Figure 8.1 Central control of respiration. The respiratory pattern is generated in the

medulla. Efferent projections from the respiratory pattern generator synapse on respi-
ratory muscle motor neurons in the spinal cord to control respiratory muscle, dia-
phragm, and intercostal muscle contraction. This drives expansion and contraction of
the lung and chest wall to move air through the respiratory tract and allows O 2 to
be exchanged for CO 2 at the level of the alveolar capillaries. The resultant changes
in P O 2 , P CO ð Þ, and pH are monitored by chemoreceptors, which then feedback onto
the RPG to modulate breathing. Lung, chest wall, and diaphragmatic activity are mon-
itored by mechanoreceptors, which also feed back onto the medullary pattern gener-
ator. Connections to the pattern generator from the cortex allow for conscious
modulation of breathing.

DRG and VRG both contain neurons that project directly to respiratory
motor neurons within the spinal cord, where they can directly drive the
RR and rhythm, and to nonmotor medullary respiratory neurons, where
they can indirectly influence RR and rhythm. 1

2.2. Airway control
Airway resistance is modulated in an inverse relationship with airway tone,
whereby increasing airway tone decreases airway resistance and vice versa.
Adequate tone of the upper airway muscles is required for airway patency.
A major purpose of the upper airway is to condition air as it passes deeper
into the respiratory tract; however, reduction of tone in laryngeal and