Functional Anatomy of Thorax

Diameters of thorax

All dimensions of thoracic cage increase during inspiration, vertical = increased by descent of diaphragm, antero posterior = increased by movement of sternum and anterior parts of ribs, lateral = increased by movements of lateral parts of ribs

Movement of ribs - pump handle

Upper ribs two to five, increased ap diameter, movement axis = along neck of rib, superior and anterior movement of sternum and anterior part of ribs

Movement of ribs - bucket handle

Lower ribs eight to ten, increased lateral diameter, movement axis = through costovertebral and sternocostal joints, elevation of lateral shaft of ribs

Diaphragm

Covers thoracic outlet, prime mover for inspiration

Attachments of diaphragm

Bodies and ivd l1 to l3, inner surface of ribs seven to twelve and their costal cartilages, posterior surface of xiphoid process, central tendon

Abdominal aorta

t12, behind diaphragm, not affected by diaphragm contraction

Oesophagus

t10, through muscle of diaphragm, sealed closed by diaphragm contraction

Inferior vena cava

t8, through central tendon, opened by diaphragm contraction

Intercostal muscles

From lower border of one rib to upper border of rib below, internal external and innermost layers, stiffen space between ribs, role in breathing and posture

Accessory muscles of inspiration

Any muscle attaching to the ribs from above and can elevate the ribs to increase thoracic volume

Expiratory muscles

Largely passive in awake humans, diaphragm contracts eccentrically for a short period at the commencement of expiration to slow expiratory rate

Muscles for quiet inspiration

Diaphragm

Muscles of force inspiration

Serratus posterior superior, pec major and minor, serratus anterior, sternocleidomastoid, scalenes, external intercostals, diaphragm

Muscles of quiet expiration

Relaxation of diaphragm, mostly passive recoil

Muscles for forced expiration

Serratus posterior inferior, abdominal muscles, quadratus lumborum, internal intercostals, subcostals