Which of the following is NOT categorized as a muscle of inspiration in the material?

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Multiple Choice

Which of the following is NOT categorized as a muscle of inspiration in the material?

Inspiration depends on muscles that expand the thoracic cavity. The diaphragm contracts to drop and increase vertical space, while the external intercostal muscles lift the ribs to widen the chest. When breathing is deep or labored, accessory muscles kick in, such as the sternocleidomastoid and scalenes to lift the upper chest, and the pectoralis minor to elevate the upper ribs when the arms are fixed. Pectoralis major, however, is a large chest muscle whose main role is moving the arm—flexion, adduction, and internal rotation of the humerus. It does not reliably elevate the ribs or expand the thoracic cavity in normal respiration, and in the material it isn’t listed among the muscles used for inspiration. That’s why it’s not categorized as an inspiratory muscle. The other listed muscles either rise the ribs or assist in chest expansion during breathing, which is why they are considered part of the inspiratory group.

Inspiration depends on muscles that expand the thoracic cavity. The diaphragm contracts to drop and increase vertical space, while the external intercostal muscles lift the ribs to widen the chest. When breathing is deep or labored, accessory muscles kick in, such as the sternocleidomastoid and scalenes to lift the upper chest, and the pectoralis minor to elevate the upper ribs when the arms are fixed.

Pectoralis major, however, is a large chest muscle whose main role is moving the arm—flexion, adduction, and internal rotation of the humerus. It does not reliably elevate the ribs or expand the thoracic cavity in normal respiration, and in the material it isn’t listed among the muscles used for inspiration. That’s why it’s not categorized as an inspiratory muscle. The other listed muscles either rise the ribs or assist in chest expansion during breathing, which is why they are considered part of the inspiratory group.

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