The primary muscle involved in normal quiet breathing is?

• A. Rectus abdominis
• B. Diaphragm
• C. Internal intercostals
• D. External obliques

Answer: (B)

The diaphragm is the primary muscle involved in normal quiet breathing, also known as tidal respiration. This dome-shaped muscle separates the thoracic cavity from the abdominal cavity and plays a crucial role in the mechanics of breathing. During inhalation, the diaphragm contracts and moves downward, increasing the volume of the thoracic cavity and allowing air to flow into the lungs. This movement creates a negative pressure within the thorax, facilitating the intake of air.

While other muscles contribute to the process of breathing, especially during exertion or in respiratory distress, the diaphragm is the main muscle engaged in quiet breathing. Its efficiency in changing thoracic volume makes it an essential component of respiratory physiology, ensuring that adequate ventilation occurs with minimal effort. This is particularly relevant in a state of rest, where the body requires baseline oxygen levels without the need for accessory respiratory muscles.