Which of these muscles is not involved with the inspiration of air?
a. diaphragm c. scalenes
b. external intercostals d. transversus thoracis
The correct answer and explanation is :
Correct Answer:
d. Transversus thoracis
Explanation:
The process of inspiration (inhalation) involves several muscles that expand the thoracic cavity, allowing air to enter the lungs due to a pressure gradient. The primary muscles responsible for inspiration include the diaphragm, external intercostals, and scalenes.
- Diaphragm (Option A):
- The diaphragm is the most important muscle for inspiration. It contracts and moves downward, increasing the vertical dimension of the thoracic cavity and decreasing intrapulmonary pressure, allowing air to flow into the lungs.
- External Intercostals (Option B):
- These muscles are located between the ribs and assist in elevating the ribcage during inspiration. By pulling the ribs upward and outward, they help expand the thoracic cavity and facilitate air intake.
- Scalenes (Option C):
- These are accessory muscles of inspiration located in the neck. They elevate the first and second ribs, assisting in deep or forced inhalation, particularly during exercise or respiratory distress.
- Transversus Thoracis (Option D) – Not Involved in Inspiration:
- The transversus thoracis is a thin muscle on the inner surface of the anterior thoracic wall. Instead of assisting in inspiration, it functions primarily during forced expiration. It helps pull the ribs downward, reducing thoracic volume and pushing air out of the lungs.
- Since expiration is usually a passive process, the transversus thoracis only becomes active during forced expiration, such as during vigorous exercise or coughing.
Conclusion:
Because the transversus thoracis is involved in expiration rather than inspiration, it is the correct answer to the question. The diaphragm, external intercostals, and scalenes all contribute to expanding the thoracic cavity for inhalation.