Makindo Medical Notes

Anatomy

Diaphragm

Origin: Xiphoid process, costal margin, fascia over quadratus lumborum and psoas major muscles, vertebral bodies L1-L3
Insertion: Central tendon of the diaphragm
Action: Pushes abdominal viscera inferiorly, increasing thoracic cavity volume (inspiration)
Innervation: Phrenic nerve (C3-C5)
Artery: Musculophrenic a., superior phrenic a., inferior phrenic a.
Notes: The left crus attaches to L1-L2 vertebral bodies, the right crus attaches to L1-L3 vertebral bodies.

External Intercostal

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: Intercostal nerves (T1-T11)
Artery: Intercostal a.
Notes: 11 in number; extend from the tubercle of the rib to the costochondral junction; continuous with the external intercostal membrane anteriorly.

Innermost Intercostal

Origin: Upper borders of a rib
Insertion: Inferior margin of the rib above
Action: Keeps the intercostal space from blowing out or sucking in during respiration
Innervation: Intercostal nerves (T1-T11)
Artery: Intercostal a.
Notes: These muscles have the same fiber direction as the internal intercostal muscles, lying deep to the intercostal neurovascular bundle.

Internal Intercostal

Origin: Upper border of a rib
Insertion: Lower border of the rib above, coursing upward and medially
Action: Keeps the intercostal space from blowing out or sucking in during respiration
Innervation: Intercostal nerves (T1-T11)
Artery: Intercostal a.
Notes: 11 in number; they extend from the margin of the sternum to the angle of the rib, continuous posteriorly with the internal intercostal membrane.

Levatores Costarum

Origin: Transverse processes of C7-T11
Insertion: Rib below its origin, medial to the angle
Action: Elevates the rib
Innervation: Dorsal primary rami of spinal nerves C7-T11
Artery: Deep cervical a., intercostal aa.
Notes: Small and relatively insignificant muscles.

Subcostalis

Origin: Angle of ribs
Insertion: Angle of a rib 2-3 ribs above its origin
Action: Compresses the intercostal spaces
Innervation: Intercostal nerves
Artery: Intercostal a.
Notes: Subcostalis, transversus thoracis, and innermost intercostal muscles form the deepest intercostal muscle layer.

Transversus Thoracis

Origin: Posterior surface of the sternum
Insertion: Inner surfaces of costal cartilages 2-6
Action: Compresses the thorax for forced expiration
Innervation: Intercostal nerves 2-6
Artery: Internal thoracic a.
Notes: Transversus thoracis, subcostalis, and innermost intercostal muscles form the innermost intercostal muscle layer.