Which muscles are primarily responsible for normal ventilation?

The diaphragm and external intercostals are indeed the primary muscles responsible for normal ventilation during restful breathing. The diaphragm is the main muscle of respiration; when it contracts, it moves downward, increasing the thoracic cavity's volume and creating a negative pressure that draws air into the lungs. This action is essential for airflow during inhalation.

The external intercostal muscles work in tandem with the diaphragm. They are located between the ribs and assist in elevating the rib cage during inhalation, further expanding the chest cavity and enhancing airflow into the lungs. Together, these muscles facilitate the basic process of ventilation in a manner that is both efficient and effective for normal, quiet breathing.

In contrast, while the accessory muscles, internal intercostals, and abdominal muscles can play a role in more forceful breathing or during times of increased demand, they are not the primary muscles used for normal ventilation during quiet breathing. Understanding the roles of these different muscle groups in respiratory physiology is crucial for recognizing how the body adapts ventilation in various situations.