UNIT 3 SECOND ORDER

External intercostal - O

1. Inferior border of rib above

External intercostal - I

1. Superior border of rib below

External intercostal - A

1. Elevates ribs

2. Increasing thoracic volume during forced inspiration

External intercostal - N

1. Intercostal nerves (T1-T11)

   • Ventral rami

External intercostal - B

1. Posterior intercostal arteries (from thoracic aorta)

2. Anterior intercostal branches (internal thoracic artery)

External intercostal clinical significance

1. Targeted in regional anesthesia (intercostal nerve blocks) for wall procedures

Internal intercostal - O

1. Inferior margin of costal groove

2. Adjacent costal cartilage

   • Inferior border of the rib above

Internal intercostal - I

1. Superior border of next rib below

Internal intercostal - A

1. Interosseous part: depresses ribs during forced expiration

2. Interchondral part: elevates ribs

Internal intercostal - N

1. Intercostal nerves (T1-T11)

   • Ventral rami

Internal intercostal - B

1. Anterior intercostal arteries

2. Posterior intercostal arteries

   • From internal thoracic and thoracic aorta

Internal intercostal clinical significance

1. Susceptible to strain injuries in activities involving repetitive twisting or forceful breathing

Innermost intercostal - O

1. Internal surface of ribs costal groove

Innermost intercostal - I

1. Superior border of rib below

Innermost intercostal - A

1. Assist internal intercostals in depressing ribs during forced expiration

Innermost intercostal - N

1. Intercostal nerves (T1-T11)

   • Ventral rami

Innermost intercostal - B

1. Anterior intercostal arteries

2. Posterior intercostal arteries

   • Internal thoracic

   • Musculophrenic arteries

Subcostal - O

1. Internal surface of lower ribs near angles

Subcostal - I

1. Superior borders (internal surface) of second or third rib inferior

Subcostal - A

1. Depresses ribs

2. Possibly aiding forced expiration

Subcostal - N

1. Intercostal nerves

Subcostal - B

1. Posterior intercostal arteries

2. Muscular branches from internal thoracic artery

Subcostal clinical significance

1. Strain can occur in athletes or laborers performing repetitive, forceful torso rotations

   • Particularly with inadequate core conditioning

Transversus thoracis - O

1. Posterior surface of lower sternum

2. Xiphoid process

Transversus thoracis - I

1. Internal surfaces of costal cartilages 2-6

Transversus thoracis - A

1. Weakly depresses ribs during expiration

2. Supports thoracic wall

Transversus thoracis - N

1. Intercostal nerves (T2-T6)

Transversus thoracis - B

1. Intercostal arteries

   • Internal thoracic artery

   • Anterior intercostal arteries

Transversus thoracis clinical significance

1. Functionally minor

2. Obstacle during internal thoracic artery harvest for coronary artery bypass grafting

Diaphragm - O

1. Xiphoid process

2. Costal cartilages of ribs 7-12

3. Lumbar vertebrae via crura

Diaphragm - I

1. Central tendon

Diaphragm - A

1. Contracts to increase vertical thoracic volume during inspiration

   • Assists in:

     • Micturition (urination)

     • Defecation

     • Parturition (childbirth)

     • Venous and lymphatic return

     • Core pressure modulation

Diaphragm - N

1. Phrenic nerve (C3-C5)

Diaphragm - B

1. Pericardiophrenic artery - central

2. Musculophrenic artery - anterior

3. Superior phrenic arteries - posterior superior

4. Inferior phrenic arteries - inferior

5. Lower intercostal arteries

Phrenic nerve clinical significance

1. Thoracic surgery or trauma can result in diaphragmatic paralysis