INTERCOSTAL NERVES & NEURALGIA

The intercostal nerves are part of the somatic nervous system and arise from the anterior rami of the thoracic spinal nerves from T1 to T11.

The intercostal nerves are distributed chiefly to the thoracic pleura and abdominal peritoneum and differ from the anterior rami of the other spinal nerves in that each pursues an independent course without plexus formation.

• The first two nerves supply fibers to the upper limb and thorax; 
• the next four are distributed to the walls of the thorax; 
• the lower five supply the walls of the thorax and abdomen.
• The 7th intercostal nerve ends at the xiphoid process of the sternum.
• The 10th intercostal nerve terminates at the navel.
• The 12th(subcostal) thoracic is distributed to the walls of the abdomen and groin.

Each of these fibers contains around 1300 axons.

Unlike the nerves from the autonomic nervous system that innervate the visceral pleura of the thoracic cavity, the intercostal nerves arise from the somatic nervous system. This enables them to control the contraction of muscles, as well as provide specific sensory information regarding the skin and parietal pleura. 

This explains why damage to the internal wall of the thoracic cavity can be felt as a sharp pain localized in the injured region. Damage to the visceral pleura is experienced as an un-localized ache.

Branches

Numerous slender, muscular filaments supply the Intercostales, the Subcostales, the Levatores costarum, the Serratus posterior superior, and the transverse thoracic. At the front of the thorax, some of these branches cross the costal cartilages from one intercostal space to another.

• Lateral cutaneous branches (rami cutanei laterales) are derived from the intercostal nerves, about midway between the vertebræ and sternum; they pierce the Intercostales externi and Serratus anterior and divide into anterior and posterior branches.
• The anterior branches run forward to the side and the forepart of the chest and skin, the fourth nerve anterior branches supplying the areola and the mamma; those of the fifth and sixth nerves supply the upper digitations of the Obliquus externus abdominis.
• The posterior branches run backward and supply the skin over the scapula and Latissimus dorsi.