How do your muscles assist you in enabling inhalation?
a) The diaphragm and the intercostal muscles contract to elevate the ribcage and create lower pressure in the thoracic cavity
b) The diaphragm and the intercostal muscles relax to elevate the ribcage and create higher pressure in the thoracic cavity
c) The diaphragm and the intercostal muscles contract to elevate the ribcage and create higher pressure in the thoracic cavity
d) The diaphragm and the intercostal muscles relax to lower the ribcage and create lower pressure in the thoracic cavity
The Correct Answer and Explanation is:
The correct answer is:
a) The diaphragm and the intercostal muscles contract to elevate the ribcage and create lower pressure in the thoracic cavity.
Explanation:
Inhalation (breathing in) is an active process that primarily involves the muscles of respiration, mainly the diaphragm and the external intercostal muscles.
- Role of the diaphragm:
- The diaphragm is a dome-shaped muscle located at the base of the lungs.
- When you inhale, the diaphragm contracts and moves downward (flattens).
- This contraction increases the vertical dimension of the thoracic cavity (the chest cavity).
- Role of the intercostal muscles:
- The intercostal muscles lie between the ribs.
- During inhalation, the external intercostal muscles contract, causing the ribcage to move upward and outward.
- This movement increases the lateral (side-to-side) and anterior-posterior (front-to-back) dimensions of the thoracic cavity.
- Effect on thoracic cavity volume and pressure:
- When both the diaphragm contracts downward and the ribcage elevates due to intercostal contraction, the overall volume inside the thoracic cavity increases.
- According to Boyle’s law, when volume increases, pressure decreases (assuming temperature is constant).
- The pressure inside the thoracic cavity (intrapulmonary pressure) becomes lower than atmospheric pressure outside the body.
- Airflow into the lungs:
- Because gases move from areas of higher pressure to areas of lower pressure, air flows into the lungs to equalize the pressure difference.
- This inflow of air allows oxygen to enter the alveoli (tiny air sacs in the lungs), where gas exchange occurs.
Why the other options are incorrect:
- Option b: The diaphragm and intercostals do not relax to elevate the ribcage. Relaxation causes the ribcage to lower, and also the diaphragm to rise, decreasing thoracic volume.
- Option c: The muscles do contract and elevate the ribcage, but this creates lower pressure, not higher pressure, in the thoracic cavity during inhalation.
- Option d: Relaxation of muscles lowers the ribcage and diaphragm, which decreases thoracic volume and increases pressure—this happens during exhalation, not inhalation.
In summary, inhalation is made possible by the active contraction of the diaphragm and external intercostal muscles, which increase the thoracic cavity volume, thereby lowering intrathoracic pressure and allowing air to flow into the lungs.