EFFECTORS OF THE RESPIRATORY SYSTEM



Signals are, transmitted from the respiratory center to the chest bellows apparatus by (1) the phrenic nerves, which supply the diaphragm, (2) the intercostal nerves, which innervate the inter­costal and abdominal muscles, (3) the accessory cranial nerves, which supply the sternomastoid muscles, and (4) the lower cervical nerves, which supply the scalene muscles. In addition, a variety of muscles acting on the soft palate, tongue, and hydid bone maintain upper airway patency and offset the collapsing effect of the negative pres­sures generated by the respiratory muscles. Dur­ing wakefulness, both the upper airway and chest wall muscles display rhythmic inspiratory activ­ity. During sleep, upper airway muscle activity wanes, whereas diaphragmatic activation changes little.