Final answer:
The muscles that provide a significant contribution to forced exhalation are the internal intercostal muscles and abdominal muscles, which become active during activities requiring rapid expulsion of air from the lungs.
Step-by-step explanation:
The correct option : d
involves two major phases: inspiration, which fills the lungs with air, and expiration, which expels air from the lungs. During normal, quiet breathing, the diaphragm and the external intercostal muscles are the primary movers. The diaphragm contracts and flattens to increase the volume of the thoracic cavity, while the external intercostal muscles contract to lift the ribcage, thereby enlarging the chest cavity. This process is essentially passive. However, during forced exhalation, when the body requires expelling a higher volume of air, such as during physical activity or when blowing out candles, additional muscles are recruited.
The internal intercostal muscles are key contributors to forced exhalation. These muscles lie just below the external intercostals and have an opposite function. Upon contraction, they pull the ribs downward and inward, reducing the volume of the thoracic cavity and thereby increasing intra-thoracic pressure, propelling air out of the lungs. Similarly, the abdominal muscles, including the rectus abdominis, obliques, and transversus abdominis, forcefully contract during intense breathing. They assist in pushing the diaphragm upward through increasing abdominal pressure, which also aids in rapidly expelling air from the lungs.
In summary, while the diaphragm and the external intercostal muscles are essential for normal inspiration, the internal intercostals and abdominal muscles play a significant role in the process of forceful exhalation, ensuring efficient expulsion of air when needed.