Which muscles are listed as inspiration muscles?

• A. diaphragm, external intercostals
• B. pectoralis major, sternocleidomastoid
• C. internal intercostals, abdominals
• D. scalenes, pectoralis minor

Answer: (C)

When you inhale, the chest cavity expands to create negative pressure and draw air in. The main muscles that drive this are the diaphragm, which contracts to lower the floor of the thoracic cavity, and the external intercostals, which lift the ribs to widen the chest. In deeper or more forceful breathing, accessory muscles come into play, such as the scalene muscles lifting the first two ribs and the sternocleidomastoid helping lift the sternum; the pectoralis minor can assist when the arms are fixed to allow more chest expansion. Internal intercostals and the abdominal muscles, on the other hand, are primarily used to push air out during expiration by decreasing thoracic volume. So, for inspiration, the key muscles are the diaphragm and external intercostals, with potential help from the accessory muscles during heavy breathing.