Basic and Clinical Sciences (BCSE) Practice Exam – Study Guide & Practice Test

The muscles that play a crucial role in forced expiration are the internal intercostals and the abdominal muscles. During forced expiration, the internal intercostal muscles work by pulling the ribs inward and downward, which decreases the volume of the thoracic cavity and helps expel air from the lungs more forcefully. The abdominal muscles, particularly the rectus abdominis, transversus abdominis, and obliques, contract to increase abdominal pressure, pushing the diaphragm up and further aiding in expelling air from the lungs.

This coordinated action is essential in activities such as heavy exercise, coughing, or any situation that requires rapid expulsion of air. The other options include muscles that primarily contribute to inspiration or have less of a role during expiration. The diaphragm and external intercostals are involved in inhalation, whereas the serratus posterior superior and pectoralis major have a minimal role in the respiratory process. Meanwhile, the scalenus anterior and sternocleidomastoid muscles assist in elevating the ribs during inspiration, making them less relevant to forced expiration.