Muscles of Breathing | Inspiration/Inhalation

Dr. Mike explains Boyle's Law, which states that increasing a container's volume decreases its internal pressure. This principle drives breathing: the body expands the thoracic cavity to drop pressure, allowing air to rush in from the higher-pressure environment outside.

During relaxed breathing, the body primarily recruits the diaphragm and the external intercostal muscles. The diaphragm, innervated by the phrenic nerve, flattens upon contraction to increase thoracic volume, while external intercostals elevate the ribs.

When extra oxygen is needed, such as during exercise, the body recruits accessory muscles including the sternocleidomastoid, scalenes, pectoralis minor, serratus anterior, and erector spinae. These muscles work to further lift the rib cage and extend the spine to increase thoracic capacity.