6.2.3. Somatic Nerves: Intercostal Nerves, Part 2

Intercostal Nerve Distribution

This diagram shows a transverse section of the thorax at approximately the level of T3. It aims to show more accurately the rami and branches of the spinal nerves at T3. Note the following:

  • The spinal nerve divides quickly into posterior and anterior rami. The anterior ramus is the third intercostal nerve.
  • The posterior ramus provides nerve branches to the muscles and skin of the back.
  • The anterior ramus, or intercostal nerve, also gives off muscular branches; specifically they supply the external intercostal muscle fibres, the internal intercostal muscle fibres and the innermost intercostal muscle fibres. The muscular branches pierce the muscles. The intercostal nerve also gives off cutaneous (skin) branches, which are named either anterior or lateral cutaneous branches depending upon their position. These are the nerves that will determine the T3 dermatome. Finally, the intercostal nerve also gives off branches to the parietal pleura. Remember from Section 3.4. that the parietal pleura is supplied by somatic nerves that allow it to detect pressure, touch, pain and temperature.