The intercostal nerves are the somatic nerves that arise from the anterior divisions of the thoracic spinal nerves from T1 to T11. These nerves in addition to supplying the thoracic wall also supply the pleura and peritoneum.
Intercostal nerves can be divided into atypical and typical intercostal nerves:
- first two intercostal nerves (T1 and T2) in addition to supplying the thorax also give branches to the brachial plexus
- lowest five intercostal nerves (T7-T11) also supply the abdomen and peritoneum
- the remaining intercostal nerves (T3-T6) supply only the thoracic wall
First intercostal nerve
The anterior division of the first thoracic nerve divides into two branches:
- the larger exits the thorax in front of the neck of the first rib to join the brachial plexus
- the smaller branch, the first intercostal nerve, runs along the first intercostal space and ends on the front of the chest as the first anterior cutaneous branch
Second-to-sixth intercostal nerves
The anterior divisions of the second, third, fourth, fifth, and sixth thoracic nerves pass forward in the intercostal spaces below the intercostal vessels. At the back of the chest, they lie between the pleura and the posterior intercostal membranes. Later near the sternum, they cross in front of internal thoracic vessels and sternocostalis muscle. It then pierces the intercostal muscles to terminate as the anterior cutaneous branch.
- muscular branches to the intercostal muscles, subcostal muscles, serratus posterior superior muscle and transversus thoracis
- cutaneous branches: lateral cutaneous and anterior cutaneous branches
- articular branches to the rib periosteum
- branches to supply the parietal pleura
Seventh-to-eleventh intercostal nerves
The anterior divisions of the seventh, eighth, ninth, tenth, and eleventh thoracic intercostal nerves are continued anteriorly from the intercostal spaces into the abdominal wall hence they are also called thoracoabdominal nerves.
They supply the rectus abdominis muscle and terminate as anterior cutaneous branches of the abdomen supplying the cutaneous sensation to the anterior abdominal wall. The lower intercostal nerves also supply the intercostal muscles and anterior abdominal wall musculature.