Which muscles are included as accessory muscles of inspiration?

• A. Pectoralis major and minor
• B. Transverse abdominus and internal obliques
• C. Rectus abdominus and external obliques
• D. Scalenes and sternocleidomastoid

Answer: (A)

The correct answer involves the identification of accessory muscles of inspiration. Accessory muscles play a role in aiding and enhancing the process of inhalation, particularly during times of increased demand, such as during exercise or respiratory distress.

The pectoralis major and minor are indeed considered accessory muscles of inspiration. Although these muscles are primarily associated with arm movement, they can assist in elevating the rib cage when the arms are fixed, thus contributing to the expansion of the thoracic cavity during inhalation.

In contrast, the other muscle groups listed do not primarily serve this function in the context of inspiration. For instance, the transverse abdominus and internal obliques are primarily involved in forced expiration rather than inspiration. Similarly, the rectus abdominus and external obliques also primarily assist in expiration by compressing the abdominal contents and forcing the diaphragm upwards. While the scalenes and sternocleidomastoid muscles are indeed accessory muscles of inspiration, they were not the choice selected, which is why the focus here is on the pectoralis major and minor as the correct answer. These muscles clearly play an important role in expanding the rib cage to facilitate breathing.