Muscle
Innermost intercostals
Intercostal fibers deep to the main nerve and vessels
High-yield
Locate the neurovascular bundle between the internal and innermost muscles. The innermost layer is incomplete and shares the deep thoracic wall with the subcostals and transversus thoracis.
Overview
The deepest intercostal layer is most apparent along the lateral chest wall. Its fibers follow the internal intercostal direction, but the main intercostal nerve and vessels pass between these two layers.
Reference facts
- Origin
- Inner lower margin of the rib above, near the costal groove
- Insertion
- Inner upper margin of the next rib down
- Innervation
- Intercostal nerves, T1–T11
- Action
- Helps stabilize the rib spaces and acts with the interosseous internal intercostals during active expiration
- Blood supply
- Intercostal arterial branches; posterior supply is chiefly aortic, with the highest intercostal artery supplying the first two spaces
Clinical correlation
The nerve's relationship to the two deep muscle layers is important in regional anesthesia and chest-wall surgery. It also explains why injury in this plane can involve both a nerve and nearby vessels.
Frequently asked questions
What do the innermost intercostals do?
Helps stabilize the rib spaces and acts with the interosseous internal intercostals during active expiration.
What nerve innervates the innermost intercostals?
The innermost intercostals are innervated by the intercostal nerves, T1–T11.
Where do the innermost intercostals attach?
The innermost intercostals originate from the inner lower margin of the rib above, near the costal groove and insert on the inner upper margin of the next rib down.
What is the blood supply of the innermost intercostals?
Intercostal arterial branches; posterior supply is chiefly aortic, with the highest intercostal artery supplying the first two spaces.