Question

which of the following is not a part of inspiration in the respiratory cycle?
a. external intercostals contract
b. external intercostals relax
c. thoracic cavity enlarges
d. domes of diaphragm flatten

Explanation:

During inspiration (inhalation), the external intercostal muscles contract (not relax), causing the rib - cage to move upward and outward. The diaphragm contracts and flattens. These actions increase the volume of the thoracic cavity. Relaxation of the external intercostals occurs during expiration (exhalation).

Answer:

B. External intercostals relax