Basic and Clinical Sciences (BCSE) Practice Exam

The primary muscles of inspiration are the diaphragm and the external intercostals. The diaphragm is a dome-shaped muscle located beneath the lungs; its contraction during inhalation creates negative pressure in the thoracic cavity, allowing air to flow into the lungs. This is the most significant driver of normal inhalation, as it moves the base of the thoracic cavity downwards, increasing lung volume.

The external intercostal muscles, located between the ribs, play a crucial supportive role. When these muscles contract during inspiration, they elevate the ribs and expand the chest wall, further contributing to an increase in thoracic volume and enhancing airflow into the lungs. Together, the diaphragm and external intercostals account for the majority of the mechanical work involved in normal breathing.

While other muscles mentioned may assist in forced inspiration or are involved in expiration, the diaphragm and external intercostals are the primary muscles responsible for the act of inhalation in typical circumstances.