Innermost intercostal muscles
The innermost intercostal muscles are muscles of respiration. They are the deepest intercostal muscles located in the intercostal spaces, and contract along with the internal intercostal muscles to reduce the transverse dimension of the thoracic cavity during expiration.
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Gross anatomy
The innermost intercostal muscles are the most deep muscle of the three intercostal muscles and arise from the inner margin of the costal groove of the rib above. The fibers run in a downwards, backwards and lateral (like the internal intercostal muscles and perpendicular to the external intercostal muscles) direction and insert into the superior border of the rib below. Some authors describe the muscle continuing over several ribs and intercostal spaces, as opposed to the internal and external intercostal muscles which only span each intercostal space 1.
As their name indicates, they are internal to the internal and external intercostal muscles. Variably, the muscles become continuous anteriorly with the tranversus thoracis muscles and posteriorly with the subcostal 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
Innermost intercostal muscle contraction causes reduction in volume of the thoracic cavity in the transverse dimension, expelling air from the lungs during expiration. They are probably the weakest of the 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)
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- pleura
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bronchopulmonary segmental anatomy (Boyden Classification) (mnemonic)
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heart
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coronary arteries
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left main coronary artery (LMCA)
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circumflex artery (LCx)
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pericardium
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pericardial recesses
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