What is the significance of the accessory muscles of breathing?

• A. They are crucial for normal expiration
• B. They are primarily used during rest
• C. They assist during heavy exertion
• D. They filter air entering the lungs

Answer: (C)

The accessory muscles of breathing play an important role in enhancing respiratory function, particularly during periods of increased physical demand, such as heavy exertion. During intense exercise or situations requiring increased ventilation, these muscles—such as the scalenes, sternocleidomastoid, and pectoralis major—engage to assist the primary muscles of respiration, like the diaphragm and external intercostals. This recruitment allows for a greater increase in total lung volume and airflow, facilitating more effective gas exchange when the body requires elevated oxygen consumption and greater removal of carbon dioxide.

In contrast, the other choices do not accurately represent the primary function of accessory muscles. They are not essential for normal expiration; rather, expiration is primarily a passive process at rest. While accessory muscles are particularly valuable during exertion, they are not primarily used during rest. Additionally, filtering air entering the lungs is a function performed by structures such as the nasal passages and mucous membranes, not the accessory muscles themselves. Thus, their significance is indeed rooted in their ability to support breathing when increased ventilation is necessary.