Final answer:
The muscles of expiration include the internal intercostal and abdominal muscles, particularly the rectus abdominis, which applies pressure to expel air during expiration and is involved in the Valsalva maneuver. The diaphragm and the external intercostal muscles aid in breathing.
Step-by-step explanation:
The muscles responsible for expiration include the 11 pairs of internal intercostal muscles, which help contract the rib cage, and the abdominal muscles, notably the rectus abdominis. The rectus abdominis plays a crucial role not only in forced expiration but also in stabilizing the core, flexing the lumbar spine, and assisting in processes like defecation, urination, and childbirth through the Valsalva maneuver.
During expiration, the rectus abdominis, along with the internal oblique and transversus abdominis muscles, applies pressure to the abdominal organs. This action increases intra-abdominal pressure and helps push air out of the lungs. The rectus abdominis is also fundamental in stabilizing the pelvic region during movements and providing a strong wall for the internal organs.
The diaphragm is the primary muscle of breathing, and its contraction is essential for inspiration, while relaxation aids in expiration. The trachea, located within the neck and upper chest, is vital for providing a passage for air to travel to and from the lungs, facilitating the process of breathing. Also, the 11 pairs of superficial external intercostal muscles assist in the inhalation process by raising the rib cage and expanding the thoracic cavity.