A Level Biology Practice Exam

What is the primary function of intercostal muscles during inhalation?

1. Pull the ribs downwards

2. Stabilize the rib cage

3. Pull the ribs upwards

4. Assist with digestive movements

The correct answer is: Pull the ribs upwards

The primary function of intercostal muscles during inhalation is to pull the ribs upwards. When we inhale, the external intercostal muscles contract, which increases the volume of the thoracic cavity. This upward movement of the ribs helps to lower the pressure inside the lungs compared to the atmospheric pressure, allowing air to flow into the lungs. This mechanism is essential for effective breathing, as the increase in thoracic volume leads to a decrease in intra-alveolar pressure, causing air to rush in. The intercostal muscles work in coordination with the diaphragm, which also contracts during inhalation, further expanding the thoracic cavity. Other options do not accurately describe the primary role of intercostal muscles during inhalation. For example, pulling the ribs downwards occurs during exhalation, while stabilizing the rib cage is a function that may be more relevant during other movements rather than specifically during inhalation. Assisting with digestive movements is unrelated to the respiratory function of the intercostal muscles.