intrinsic thorax muscles

Question 1

external intercostal

Answer 1

• origin: lower border of a rib within an intercostal space
• insertion: upper border of the rib below, coursing, downward and medially
• action: raises ribs during inspiration
• 11 from tubercle of rib to costochondral junction; continuous with the external intercostal membrane anteriorly

Question 2

internal intercostal

Answer 2

• origin: upper border of a rib
• insertion: lower border of rib above, coursing up and medially
• action: lowers ribs during expiration
• 11 from margin of sternum to angle of rib, continuous posteriorly with the internal intercostal membrane

Question 3

innermost intercostal

Answer 3

• origin: upper borders of a rib
• insertion: fibers course up and medially to insert on the inferior margin of the rib above
• action: lowers ribs during expiration

Question 4

levatores costarum

Answer 4

• origin: transverse processes C7-T11
• insertion: superior border of rib below
• action: elevates rib: inspirator

Question 5

diaphragm

Answer 5

• origin: xiphoid process, lower 6 costal cartilages, vertebral bodies L1-L3
• insertion: central tendon of the diaphragm
• action: pushes the abdominal viscera inferiorly, increasing the volume of the thoracic cavity (inspiration)

Question 6

subcostals

Answer 6

• origin: angle of ribs
• insertion: angle of a rib 2-3 above
• action: depresses ribs : espirator

Question 7

transversus thoracis

Answer 7

• origin: lower posterior surface of sternum
• insertion: costal cartilages of last 3-4 true ribs
• action: compress the thorax for forced expiration/depresses costal cartilage: espirator