Which muscles contract to decrease thoracic volume and raise intrapulmonary pressure during expiration?

• A. Internal intercostal muscles and abdominal muscles
• B. Sternocleidomastoid and scalene muscles
• C. Pectoralis minor and serratus anterior muscles
• D. Diaphragm and external intercostal muscles

Answer: (A)

Verified step by step guidance

1. Understand the process of expiration: During expiration, the thoracic volume decreases, and intrapulmonary pressure increases, forcing air out of the lungs.
2. Identify the muscles involved in expiration: The primary muscles that contract to decrease thoracic volume are the internal intercostal muscles and the abdominal muscles.
3. Differentiate between muscles used in inspiration and expiration: The diaphragm and external intercostal muscles are primarily involved in inspiration, not expiration.
4. Consider accessory muscles: Sternocleidomastoid and scalene muscles are accessory muscles used during forced inspiration, not expiration.
5. Evaluate the role of other muscles: Pectoralis minor and serratus anterior muscles are involved in movements of the shoulder girdle and are not primarily responsible for expiration.