Muscles of the Thorax

Question 1

Diaphragm

Answer 1

Origin Xiphoid process, costal margin, fascia over quadratus lumborum and
psoas major mm. (lateral & medial arcuate ligaments), vertebral bodies
of L 1-L3
Insertion Central tendon of the diaphragm
Action Pushes the abdominal viscera inferiorly, increasing the volume of the
thoracic cavity (inspiration)
Innervation Phrenic nerve (C3-C5)
Artery Musculophrenic a. , superior phrenic a., inferior phrenic a.

Question 2

External lntercostals

Answer 2

Origin Lower border of a rib within an intercostal space
Insertion Upper border of the rib below, coursing downward and medially
Action Keeps the intercostal space from blowing out or sucking in during
respiration
Innervation I ntercostal nerves (T1-T11)
Artery lntercostal a.

Question 3

Innermost lntercostals

Answer 3

Origin Upper border of a rib
Insertion Fibers course up and medially to insert on the inferior margin of the rib
above
Action Keeps the intercostal space from blowing out or sucking in during
respiration
Innervation lntercostal nerves (T1-T11)
Artery lntercostal a.

Question 4

Internal lntercostals

Answer 4

Origin Upper border of a rib
Insertion Lower border of rib above, coursing up and medially
Action Keeps the intercostal space from blowing out or sucking in during
respiration
Innervation lntercostal nerves (T1-T11)
Artery lntercostal a.

Question 5

Levatores Costarum

Answer 5

Origin TVPs of C7-T11
Insertion Rib below its origin, medial to the angle
Action Elevates the rib
Innervation Dorsal primary rami of C7-T11 spinal nerves
Artery Deep cervical a. , intercostal aa.

Question 6

Serratus Posterior Inferior

Answer 6

Origin Thoracolumbar fascia, SPs of T11-L2
Insertion Ribs 9-12, lateral to the angles
Action Pulls down lower ribs
Innervation Branches of the ventral primary rami of T9-T12 spinal nerves
Artery Lowest posterior intercostal a., subcostal a., first 2 lumbar aa.

Question 7

Serratus Posterior Superior

Answer 7

Origin Nuchal ligament, SPs of C7-T3
Insertion Ribs 1-4, lateral to the angles
Action Elevates the upper ribs
I Innervation Branches of the ventral primary rami of T1-T 4 spinal nerves
Artery Posterior intercostal aa. 1-4

Question 8

Subcostalis

Answer 8

Origin Angle of ribs
Insertion Angle of a rib 2-3 ribs above origin
Action Compresses the intercostal spaces
Innervation lntercostal nerves
Artery lntercostal a.

Question 9

Transversus Thoracis

Answer 9

Origin Posterior surface of the sternum
Insertion Inner surface of costal cartilages 2-6
Action Compresses the thorax for forced expiration
Innervation lntercostal nerves 2-6
Artery Internal thoracic a.