Intercostal nerves

The anterior branches of the thoracic spinal nerves (ThI-ThXII) retain a metameric (segmental) structure. The eleven upper pairs of anterior branches are called intercostal nerves, the 12th intercostal branch is called the subcostal nerve. The intercostal nerves innervate all the muscles and skin of the lateral and anterior sections of the chest and abdominal walls, the parietal pleura and peritoneum, and the mammary gland.

The intercostal nerves (nn. intercostales) are directed laterally and forward in the intercostal spaces, the subcostal nerve - under the 12th rib. Each intercostal nerve passes at the lower edge of the corresponding rib under the artery and vein of the same name. From the place of origin to the angle of the rib, the nerves are covered by the endocostal fascia and the costal part of the pleura. Further forward, each of the nerves goes between the external and internal intercostal muscles. Six pairs of lower intercostal nerves pass through the costal part of the diaphragm. Then they go obliquely forward and downward between the internal oblique and transverse abdominal muscles, giving off branches to them. The subcostal nerve passes on the outer side of the quadratus lumborum muscle.

The muscular branches (rr. musculares) of the intercostal nerves innervate the external and internal intercostal muscles, the subcostal muscles; the muscles that raise the ribs; the transverse thoracic muscle, the posterior superior serratus muscle, the external and internal oblique, the transverse and rectus abdominis muscles.

The cutaneous branches of the intercostal nerves are the anterior and lateral cutaneous branches (r. cutaneus lateralis et r. cutaneus anterior). Depending on their location, there are anterior and lateral cutaneous branches of the chest and abdomen. The lateral cutaneous branches on their way to the subcutaneous tissue pass between the teeth of the anterior serratus muscle (in the chest area), and below they pierce the external oblique muscle of the abdomen. The lateral cutaneous branches of the IV-VI intercostal nerves participate in the innervation of the mammary gland (lateral branches of the mammary gland, rr. mammarii laterales). Secretory vegetative (sympathetic) fibers also approach the gland as part of these branches. The lateral cutaneous branches of the second and third intercostal nerves connect with the medial cutaneous nerve of the arm. These connections are called the intercostobrachial nerves (nn. intercostobrachiales).

The anterior (ventral) cutaneous branches of the upper six intercostal nerves emerge into the skin near the edge of the sternum, piercing the pectoralis major muscle. In the abdominal region, the anterior branches of the seventh through twelfth intercostal nerves pierce the rectus abdominis muscle and the anterior leaflet of its sheath and branch out in the skin above this muscle.

The anterior cutaneous branch of the subcostal nerve emerges subcutaneously just below the line drawn between the navel and the pubis. The anterior branches of the II-IV intercostal nerves in women are called the medial branches of the mammary gland (rr. mammarii mediales), they give off branches to the mammary gland.

The branches of the intercostal nerves innervate the costal and diaphragmatic parts of the pleura, the parietal peritoneum of the anterolateral wall of the abdominal cavity and the diaphragm.

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