Pulmonary ventilation is controlled by respiratory centers in the brain stem. The inspiratory center controls the motor neurons that innervate the diaphragm and external intercostal muscles, while the expiratory center controls the motor neurons that innervate the accessory muscles responsible for active exhalation. Given what you know about eupnea and hyperpnea, which of the following statements about these centers is correct? a. During eupnea, only the inspiratory center is active.
b. During eupnea, neither center is active.
c. During eupnea, both the inspiratory and expiratory centers are active.
d. During hyperpnea, only the inspiratory center is active.