Muscle
Internal intercostals
Middle intercostal layer with region-dependent actions
High-yield
Do not give the whole muscle one breathing action: the interosseous portion helps forced expiration, whereas the parasternal interchondral portion can assist inspiration.
Overview
Deep to the external layer, these fibers take a different oblique direction between adjacent ribs. Muscle extends from the sternum toward the rib angles; farther posteriorly, an internal intercostal membrane continues the layer.
Reference facts
- Origin
- Upper edge of the lower rib in an intercostal space
- Insertion
- Lower edge and costal-groove region of the rib above
- Action
- Interosseous fibers help lower ribs during forced expiration; interchondral fibers can help elevate them
- Innervation
- Intercostal nerves from thoracic anterior rami, T1–T11
- Blood supply
- Anterior and posterior intercostal arterial branches
Frequently asked questions
What do the internal intercostals do?
Interosseous fibers help lower ribs during forced expiration; interchondral fibers can help elevate them.
What nerve innervates the internal intercostals?
The internal intercostals are innervated by the intercostal nerves from thoracic anterior rami, T1–T11.
Where do the internal intercostals attach?
The internal intercostals originate from the upper edge of the lower rib in an intercostal space and insert on the lower edge and costal-groove region of the rib above.
What is the blood supply of the internal intercostals?
Anterior and posterior intercostal arterial branches.