2 – Anatomy of the intercostal nerve

The spinal nerve is formed by the union of the dorsal sensory root and the ventral motor root

It passes the intervertebral foramen and branches into a ventral and a dorsal ramus. The dorsal ramus innervates the intrinsic back muscles. The ventral ramus of the intercostal nerves run anterior together with the intercostal artery and vein between two adjacent ribs sandwiched between the socalled innermost intercostal muscle (the deepest intercostal muscle layer just separated from the parietal pleura by the endothoracic fascia) and the internal intercostal muscle (the middel intercostal muscle layer). The outermost intercostal muscle layer is called the external intercostal muscle.

In the midaxillary line the intercostal nerve gives off a lateral cutaneous branch that pierces the internal and external intercostal muscles and innervates the lateral thoracic wall

Anteriorly the intercostal nerve terminates in the anterior cutaneous branch that innervates the skin covering the medial part of the trunk