Quick Facts
Origin: Eighth thoracic nerve.
Course: Travels within the eighth intercostal space.
Branches: Collateral, lateral cutaneous, and anterior cutaneous branches.
Supply: The anterior ramus supplies motor innervation to the muscles of the eighth intercostal space and abdominal muscles. It also conveys sensory innervation from the skin of the abdominal wall.
Related parts of the anatomy
Origin
The anterior ramus of eighth thoracic nerve (or eighth intercostal nerve) is one of two branches of the eighth thoracic nerve, the other being the posterior ramus.
Course
The anterior ramus passes forward, lying between the pleura of the lungs and the internal intercostal membranes. It then enters the space between the internal intercostal and innermost intercostal muscles to course through the eighth intercostal space. It is also accompanied by an intercostal artery and vein, where the vein sits closest to the rib above, followed by the artery and nerve.
As the anterior rami of the seventh to eleventh thoracic nerves leave the intercostal space, they continue anteriorly into the abdominal wall. They course between the transversus abdominis and internal abdominal oblique muscles. They then enter the lateral margin of the rectus sheath, passing posterior to the rectus abdominis muscle. They pierce the rectus abdominis muscle and the anterior rectus sheath to pass anteriorly to the overlying skin.
Branches
Near its origin, the anterior ramus of the eighth thoracic nerve gives off a collateral branch that descends in the intercostal space and courses along the inferior border of the space, in the same plane as the anterior ramus itself.
The lateral cutaneous branch of the anterior ramus of eighth thoracic nerve branches from the anterior ramus around the mid-axillary line. It briefly accompanies the nerve before piercing through the chest wall. The lateral branch further subdivides into anterior and posterior branches that supplying the overlying skin.
The anterior cutaneous branch arises as the anterior ramus of eighth thoracic nerve pierces the anterior rectus sheath.
Supplied Structures & Function
The anterior ramus of the eighth thoracic nerve supplies the intercostal muscles of the eighth intercostal space (external intercostal, internal intercostal, innermost intercostal). It also supplies motor innervation to most of the abdominal muscles (rectus abdominis, external abdominal oblique, internal abdominal oblique, transversus abdominis) and sensory innervation from the anterolateral abdominal wall. Sensory fibers also extend to the costal parts of diaphragm and parietal peritoneum.
List of Clinical Correlates
—Referred pain
—Transversus abdominis plane (TAP) block
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Intercostal Nerve
Slipping rib syndrome is produced by impingement of an intercostal nerve between two costal cartilages, secondary to the subluxation of an interchondral articulation.
