Internal Intercostal Muscle (Left) (Musculus intercostalis internus)
Educational content only — not medical advice.
Anatomy
The middle intercostal layer, its fibres running downward and backward — perpendicular to the external layer, like the internal oblique of the abdomen. It is complete anteriorly from the sternum to the rib angle, and behind the angle it continues as the internal intercostal membrane. The intercostal vessels and nerve run in its costal-groove surface.
Origin & insertion
From the costal groove of each rib and its costal cartilage, to the upper border of the rib below.
Action
Depresses the ribs in forced expiration and, with the other layers, stiffens the intercostal space.
Innervation
Intercostal nerves (T1–T11).
Clinical notes
Because the neurovascular bundle lies between the internal and innermost layers, an intercostal nerve block is placed in this plane; its anterior completeness also matters when chest-wall incisions are designed to spare the membrane-supported spaces.
Related structures
Educational references
FAQ
What is the role of the Internal Intercostal Muscle (Left)?
The middle intercostal layer, its fibres running downward and backward — perpendicular to the external layer, like the internal oblique of the abdomen. It is complete anteriorly from the sternum to the rib angle, and behind the angle it continues as the internal intercostal membrane. The intercostal vessels and nerve run in its costal-groove surface.
Why is the Internal Intercostal Muscle (Left) clinically important?
Because the neurovascular bundle lies between the internal and innermost layers, an intercostal nerve block is placed in this plane; its anterior completeness also matters when chest-wall incisions are designed to spare the membrane-supported spaces.
Source & license
BodyParts3D, © The Database Center for Life Science licensed under CC Attribution 4.0 International (https://creativecommons.org/licenses/by/4.0/). license details