Which muscle is primarily responsible for inspiration during quiet breathing?

• A. Scalenes
• B. Abdominals
• C. Diaphragm
• D. Internal intercostals

Answer: (C)

The diaphragm is the primary muscle responsible for inspiration during quiet breathing. This dome-shaped muscle is situated beneath the lungs, separating the thoracic cavity from the abdominal cavity. When the diaphragm contracts, it flattens and moves downward, increasing the volume of the thoracic cavity. This volume increase creates a negative pressure within the lungs, allowing air to flow in from the atmosphere, facilitating the process of inhalation.

During quiet breathing, the diaphragm is sufficient to meet the demands of ventilation without the need for accessory muscles. It operates primarily through passive mechanisms, taking advantage of the natural elasticity of the lungs and thorax. While other muscles can assist in more forceful breathing or during periods of increased demand, the diaphragm remains the dominant muscle for quiet inspiration in a resting state. Understanding the role of the diaphragm is crucial for comprehending how our respiratory system functions efficiently during normal, day-to-day activities.