Muscles of Respiration Anatomy
Accessory Quiet breathing, Sternocleidomastoid (elevates sternum), Expiration results from passive recoil
of lungs and rib cage, Scalene muscles, Anterior, Middle, Posterior (elevate and fix upper ribs), Principal, Internal intercostal muscles, except interchondral
part (aid forced expiration), Abdominals (depress lower ribs, compress abdominal contents, thus pushing
up respiratory diaphragm, aiding forced expiration), Rectus abdominis, External abdominal oblique muscle, Internal abdominal oblique muscle.
Transversus abdominis muscle, Active breathing, External intercostals, most superficial (elevate ribs,
thus increasing width of thoracic cavity and aiding deep inspiration), Interchondral parts of internal intercostals
are deep to external intercostals (also elevate ribs and aid external intercostals with deep
inspiration), Respiratory diaphragm (domes descend, thus increasing vertical dimension of
thoracic cavity; also elevates lower ribs)
