External intercostal muscle
The external (or outermost) intercostal muscles are important muscles of respiration. They number eleven on each side and are located in the intercostal space, expanding the transverse dimension of the thoracic cavity during inspiration.
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Gross anatomy
The external intercostal muscles are the outermost muscle of the three intercostal muscles and arise from the lower border of the rib above the respective intercostal space. The fibers run in a downwards, forwards and medial direction and insert into the outer lip of the superior border of the rib below. At their insertion they end in thin anterior intercostal membranes that continue towards the sternum. Anteriorly the lower muscles become continuous with the external oblique muscles in the anterolateral abdominal wall. As their name indicates, they are external to the internal intercostal muscles.
Blood supply
- arterial supply: anterior and posterior intercostal arteries
- venous drainage: internal thoracic vein and intercostal veins
Innervation
Muscular branches from the intercostal nerves of the respective intercostal space (T1-T11), which run with the intercostal vessels under the costal groove in between the internal and innermost intercostal muscles.
Action
External intercostal muscle contraction causes expansion of the thoracic cavity in the transverse dimension and causes an influx of air into the lungs during inspiration. They are stronger than the internal intercostal muscles.
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Anatomy: Thoracic
- thoracic skeleton
- thoracic cage
- thoracic spine
- articulations
- muscles of the thorax
- diaphragm
- intercostal space
- intercostal muscles
- variant anatomy
- spaces of the thorax
- thoracic viscera
- tracheobronchial tree
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lungs
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bronchopulmonary segmental anatomy (Boyden Classification) (mnemonic)
- left lung
- right lung
- variant anatomy
- lung parenchyma
- hilum
- pleura
-
bronchopulmonary segmental anatomy (Boyden Classification) (mnemonic)
-
heart
- cardiac chambers
- heart valves
- pectinate muscles
- cardiac fibrous skeleton
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coronary arteries
- coronary arterial dominance
- myocardial segments
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left main coronary artery (LMCA)
- ramus intermedius artery (RI)
-
circumflex artery (LCx)
- obtuse marginal branches (OM1, OM2, etc))
- Kugel's artery
-
left anterior descending artery (LAD)
- diagonal branches (D1, D2, etc)
- septal perforators (S1, S2, etc)
-
right coronary artery (RCA)
- conus artery
- sinoatrial nodal artery
- acute marginal branches (AM1, AM2, etc)
- inferior interventricular artery (PDA)
- posterior left ventricular artery (PLV)
- congenital anomalies
- innervation of the heart
- fetal circulation
- atrial septum
- endocardium
- myocardium
-
pericardium
- epicardium
- epicardial fat pad
- pericardial space
- oblique pericardial sinus
- transverse pericardial sinus
-
pericardial recesses
- aortic recesses
- pulmonic recesses
- postcaval recess
- pulmonary venous recesses
- pericardial ligaments
- esophagus
- thymus
- breast
- blood supply of the thorax
- arteries
- veins
- superior vena cava (SVC)
- inferior vena cava (IVC)
-
coronary veins
- cardiac veins which drain into the coronary sinus
- great cardiac vein
- middle cardiac vein
- small cardiac vein
- posterior vein of the left ventricle
- vein of Marshall (oblique vein of the left atrium)
- anterior cardiac veins
- venae cordis minimae (smallest cardiac veins or thebesian veins)
- cardiac veins which drain into the coronary sinus
- pulmonary veins
- thoracoepigastric vein
- lymphatics
- innervation of the thorax
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